review the thesis
see details in documents
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Young Professionals & Students Housing With Modular Construction In Washington, DC
by
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THESIS TITLE
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14 December 2018
Thesis Seminar Class: Fall 2018
Thesis Studio VIII: Spring 2019
Degree to be Awarded: May 2020
Master of Architecture
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Table of Contents
Chapter 1: Introduction
3
1.1 Problem Statement
3
Research Question
4
Research Aim
4
Research Scope and Rationale
4
1.2 Objectives
5
Chapter 2: Background
6
2.1 Overview of Modular Construction and Modular Construction Projects
6
2.2 Dormitory in Washington D.C. and Student Population in Washington D.C
8
Chapter 3: Methodology
9
References
12
Chapter 1: Introduction
1.1 Problem Statement
The need for faster and efficient building construction is considered to be of utmost importance in the housing market with rising enrolment rates of students in universities. There is a significant focus on becoming environmentally conscious, cost-effective, innovative, as well as providing sustainable and affordable living alternatives for individuals. In this context, modular construction is beneficial for providing greener and faster benefits in resolving dormitory issues, the high cost of dormitories and a shortage of living space (Marcus, 2017). Students in Washington D.C. are facing affordability related challenges due to increasing dorm charges and high living expenses. Modular construction approaches are highly effective as they enable the in completion of the construction projects in a shorter duration than conventional construction approaches (Marcus, 2017).
Under modular construction techniques, buildings are constructed off-site in regulated environmental conditions via using same design structures, materials, codes and standards. However, several and constraints are associated with the use of modular construction approaches wherein it is identified that around 40 to 50 percent part of modular construction is left to complete on-site mainly because of transportation and structural reasons (Choi, Chen & Kim, 2017). It has been identified that inadequacies in transportation systems are creating challenges in the successful completion of modular construction projects. Further, it is stated that prefabricated construction techniques involve transportation and crane risks; thus, the use of modular construction in addressing cost issues and the lack of housing facilities for students is restricted via transportation problems. Additional, the constraints include logistics, costs, transportation, architectural design, regional manufacturing, delivery, codes and inspection (Choi, Chen & Kim, 2017). In this context, the proposal project focused on the subject of evaluating the visibility of dormitory with modular construction in Washington D.C. Modular construction can be helpful in addressing dormitory issues concerning pricing, living facilities but the use of modular construction involves transportation and cost-related challenges that need to be addressed adequately.
Research Question
The study is based on investigating the questions stated below:
R.Q.1 “What are the major dormitory related issues in Washington D.C?
R.Q. 2 “What are the potential benefits of modular construction in resolving dormitory related issues in Washington D.C?”
Research Scope and Rationale
The selected research topic has become an issue of concern with increasing costs of dormitories and lack of living space in DC also known as District of Columbia due to increased students population, who lives in off-campus as shown Table 1. Modular construction has numerous advantages in terms of unlimited design concepts and flexibility, but there is a need to eliminate key constraints and transportation limitations for leveraging its benefits and addressing dormitory issues in Washington D.C. The study outcomes can be beneficial for the construction sector along with providing a substantial contribution to the existing literature of modular construction. Exploration of the selected subject will be beneficial for the society as the demand for faster and greener construction is increasing. Hence, the research findings include strategic measures for eradicating challenges concerning modular construction techniques that can be considered by architects and construction project managers for improving their practices. Moreover, scholars and academicians can also consider this study while investigating the similar subject and exploring new dimensions of dormitory with modular construction, as well as its challenges, strategies and benefits.
1.2 Objectives
· To explore dormitory issues in Washington D.C.
This objective will explore dormitory issues existing in DC due to increased student population in the city and housing issues. Increasing population of students and shortage of housing facilities are becoming an issue of concern. Due to lack of housing facilities in the city, students are facing difficulties in getting accommodation in university campus. Along with this, cost, design and transportation related issues will also be evaluated for identifying the need for improvement in dormitories in Washington D.C.
· To examine the need and potential benefits of modular construction approaches
This objective will focus on evaluating the advantages of modular construction approaches for determining its needs and its potential contribution in resolving dormitory issues. Modular construction approaches are regarded to be advantageous for construction industry as these approaches are cost efficient and energy efficient in nature Further, information relating to reduced time duration in completion of projects based on modular construction can be helpful in understanding the need of modular construction with respect of dormitory issues.
· To analyse the challenges involved in the use of modular construction with a specific focus on cost and transportation
This objective will analyse the key challenges involved in the use of modular construction. Modular construction approaches are deemed to be beneficial in faster completion of construction projects but challenges concerning transportation of prefabricated parts hinder its widespread use. High cost is incurred in transporting prefabricated parts to installation sites. Thus, this objective will highlight prominent challenges faced in use of modular construction approaches.
· To suggest suitable measures for addressing modular construction challenges for resolving dormitory issues in Washington D.C.
This objective will be based on recommending strategic measures for addressing modular construction challenges for resolving dormitory issues prevailing in DC. The strategic measures will be suggested in the light of key challenges concerning cost and transportation problems of modular construction so that these measures can be adopted for constructing dormitories in an efficient manner.
Chapter 2: Background
2.1 Overview of Modular Construction and Modular Construction Projects
Modular construction consists of prefabricated room-sized units which are usually fully fitted and adjusted in manufacture for further installation as building blocks. The prominent benefits of modular construction are the speed of on-site installation, the economy of scale relating to the manufacturing of repeated units, improved accuracy and quality of operations (Chen, Okudan & Riley, 2010). It is examined that modular buildings can be reused and dismantled due to which its asset value is effectively maintained. Modular construction techniques enable in building a permanent and temporary building such as constructing camps, classroom and schools. Moreover, modular construction is extremely beneficial for rural or remote areas as conventional approaches to construction cannot be adopted in such area (Doran & Giannakis, 2011).
It is also asserted that modular construction is rapid and less expensive technique as this construction technique is unaffected by weather conditions and can resist earthquake forces in a better way. In the similar prospect, it is claimed that modular construction is a time-saving process under which building are manufactured off-site and then transported for installation that enables in saving time and cost involved in the site preparation process. The modular construction technique is highly preferred in today’s era as it involves prefabricated units that serve a perfect solution for addressing construction challenges in urban, rural and remote areas. Additionally, modular construction processes are sustainable and efficient in comparison to traditional construction approaches (Lu & Korman, 2010).
High rise residential building projects are undertaken within the United States (US) via the use of modular construction techniques. Multi-storey buildings ranging from four to eight are constructed with the help of a design method based on modular applications. However, pressure has been extended to this relatively emerged form of construction for building 12 storey buildings. Modular walls have been tested, and it is determined that external sheathing boards and the plasterboard protect C sections’ minor axis buckling (Lawson & Richards, 2010). Apart from this, a 57 storey skyscraper was constructed in total 19 days via utilising prefabricated modules. Tighter integration method and the bulk systems of prefabrication reduces thermal bridges. Prefabrication method provides several advantages such as improved quality, better quality control, the decrease in construction waste and reduction in on-site noise and dust (Boafo, Kim and Kim, 2016). In addition to this, it is examined that the reduction of labour and construction time are other advantages of using prefabrication. In this series, a 25-storey student residential has been built in Wolverhampton with an installation period of approximately 32 weeks. As a whole, prefabrication and use of modular construction process contributed towards reducing construction waste up to 70% that indicate positive environmental effects of modular construction. Under prefabrication single elements have been used such as gable ends, stairs, wood kits, wall frames and precast concrete (Lawson, Ogden & Bergin, 2011, pp 150-154).
The case study of the construction of 25 storey residential building in Wolverhampton depicts that modular construction methods can be utilised for improving stability against wind action when the building is constructed by steel framed core or concrete framed core. It is examined that modules utilising corner posts offer more flexibility in preparing room layouts, but corner posts modules are more expensive to manufacture in comparison to load-bearing systems utilising light steel (Lawson, Ogden & Bergin, 2011, pp. 149-153). It is evaluated that the construction period and cost was reduced with the use of modular approaches in the construction projects discussed above. It is also illustrated that modular buildings are cost-effective and sustainable, as well as they consume less time in the construction of buildings in comparison the conventional construction techniques. Overall, it has been noted that modular construction and prefabricated construction facilitate in improving the sustainability of construction practices via reducing negative environmental implications of construction practices (Quale et al., 2012, p. 247; Lawson & Richards, 2010, p.151).Modular constructions practices are also known as off-site construction technique that has several benefits in terms of reduced cost, noise, labour and other on-site activities. However, there is a need to manage transportation and crane risks involved in moving prefabricated modules to site for installation in modular construction (Chen, Okudan & Riley, 2010, p. 240).
2.2 Dormitory in Washington D.C. and Student Population in Washington D.C
As per University of District of Columbia (UDC) flagship report US census date, Georgetown University, George Washington and Catholic University witnessed surge in admission of students in 2018; wherein around 78 percent, 61 percent and 58 percent students are living in the campus of the universities respectively. Cost of housing is high in all the universities of DC with average of around 15K (UDC 2018 Flagship report). The report indicates that approximately 4805 students enrolled in 2018, out of which UDC’s require to fulfil need of housing to 1585 students that signify the dire need to take strategic actions in this regard. Increasing number of students including freshman, junior, sophomore and senior highlight the need for making housing arrangement for students in the city. It is also determined that American University and Howard University in Washington D.C. are also witnessing increase in the footfall of students and enrolment; wherein only 52 percent and 38 percent students are able to obtain accommodation in university campuses respectively (UDC 2018 Flagship report). Additionally, UDC is facing challenges in providing housing facilities to students. Overall, the data depicts that student population is rising in Washington D.C., thereby highlighting the need for rapid, energy efficient and cost-effective construction for addressing the issues of lack of accommodation.
Chapter 3: Methodology
Research methodology indicates the process of data collection and analysis so that research objectives can be fulfilled, and key questions can be answered. Research methods facilitate the researcher to investigate the chosen phenomenon and extract crucial findings in light of the main aim and core questions (Saunders, & Lewis, 2012). There are two prominent methods; qualitative methods and quantitative methods in which qualitative methods enable in carrying out the study in a subjective manner by focusing on gathering subjective perspectives and multiple viewpoints about the subject (Saunders, & Lewis, 2012). Hence, qualitative methods will be employed for conducting this study for gaining detailed information about dormitory with modular construction in Washington DC and examining the dormitory issues and advantages of modular construction methods. However, quantitative methods are also available for executing the study in which more attention is given to the objective aspects of the topic and extract facts and statistical information about the topic (Bryman, 2016; Bernard, 2017). Moreover, this particular study requires substantial information about modular construction approaches, their need, issues, challenges and strategies with specific reference to dormitory issues in Washington DC. Therefore, qualitative methods are preferred over quantitative methods.
Research design, research philosophy and research approach need to be applied in alignment with the research methods and the nature of the work. Qualitative studies support the use of interpretivism philosophy as this philosophy emphasises on subjective investigation via holding the notion that reality is consistently changing; hence the research problem cannot be addressed through a fixed set of statistical data or numerical information (Taylor, Bogdan and DeVault, 2015). The inductive approach and the exploratory design will be appropriate for gathering novel information about modular construction and its implications for addressing dormitory issues in Washington relating to increased pricing and accommodation issues due to the increased number of students. Further, the exploratory design will be applied so that the research process can be carried out in a flexible way (Taylor, Bogdan and DeVault, 2015).
Data Collection
Both primary and secondary data will be procured for accomplishing the study and obtaining relevant outcomes in which primary data will be gathered from the semi-structured interview method. Qualitative data can be obtained through primary and secondary data collection methods in which interview and focus group method are utilised for collecting first-hand data while case study method and library research method are used for gathering secondary data. Thus, the interview will be conducted with seven architects of Washington D.C. in the US for recording data about the benefits and challenges involved in the use of modular construction approaches. Data will also be gathered from interviewees for determining the role of modular construction in addressing dormitory related issues in Washington D.C. through its cost-effective, eco-friendly and faster construction techniques. Purposive sampling technique will be used for selecting participants for data collection through the interview.
Thematic analysis technique will be incorporated for examining data gathered from the interview and extract main findings in the light of objectives formed in the initial phase of the study. Ethical principles and norms of performing research will adequately comply throughout the study for maintaining reliability and quality of findings and overall research (Bryman, 2016; Bernard, 2017). Anonymity will be maintained, and consent of the participants will be taken prior to conduction of interview. Other than this, secondary data will be retrieved from academic journals and peer-reviewed articles in this study (Saunders, & Lewis, 2012).
References
UDC 2018 Flagship Report ( please remove this and nany related information in text)
Bernard, H.R. 2017. Research methods in anthropology: Qualitative and quantitative approaches. Rowman & Littlefield.
Boafo, F.E., Kim, J.H. & Kim, J.T. (2016). Performance of modular prefabricated architecture: case study-based review and future pathways. Sustainability, 8(6), 558.
Bryman, A. (2016). Social research methods. Oxford university press.
Chen, Y., Okudan, G. E., & Riley, D. R. (2010). Sustainable performance criteria for construction method selection in concrete buildings. Automation in construction, 19(2), 235-244.
Choi, J. O., Chen, X. B., & Kim, T. W. (2017). Opportunities and challenges of modular methods in dense urban environment. International Journal of Construction Management, 1-13.
Doran, D., & Giannakis, M. (2011). An examination of a modular supply chain: a construction sector perspective. Supply Chain Management: An International Journal, 16(4), 260-270.
Lawson, R.M. & Richards, J. (2010). Modular design for high-rise buildings. Proceedings of the Institution of Civil Engineers-Structures and Buildings, 163(3), 151-164.
Lawson, R.M., Ogden, R.G. & Bergin, R. (2011). Application of modular construction in high-rise buildings. Journal of architectural engineering, 18(2), 148-154.
Lu, N., & Korman, T. (2010). Implementation of building information modeling (BIM) in modular construction: Benefits and challenges. Construction Research Congress 2010: Innovation for Reshaping Construction Practice.
Marcus, J. (2017). Study: Fast-rising room and board costs worsen college affordability problem, retrieved December 11, 2018, from
Study: Fast-rising room and board costs worsen college affordability problem
Quale, J., Eckelman, M. J., Williams, K. W., Sloditskie, G., & Zimmerman, J. B. (2012). Construction matters: Comparing environmental impacts of building modular and conventional homes in the United States. Journal of industrial ecology, 16(2), 243-253.
Saunders, M. N., & Lewis, P. (2012). Doing research in business & management: An essential guide to planning your project. Pearson.
Taylor, S.J., Bogdan, R. and DeVault, M. 2015. Introduction to qualitative research methods: A guidebook and resource. John Wiley & Sons.
PAGE
iii
for young professionals
and students
Sustainable performance criteria for construction method selection in
concrete buildings
Ying Chen a,b, Gül E. Okudan c, David R. Riley b,⁎
a Department of Construction Management, School of Civil Engineering, Tsinghua University, Beijing, P.R. China
b Department of Architectural Engineering, The Pennsylvania State University, University Park, 104 Engineering Unit A, University Park, PA, USA
c Department of Industrial and Manufacturing Engineering, The Pennsylvania State University, University Park, PA, USA
a b s t r a c ta r t i c l e i n f o
Article history:
Accepted 19 October 2009
Keywords:
Construction methods
Prefabrication
Concrete construction
Construction management
Sustainable development
The use of prefabrication offers significant advantages, yet appropriate criteria for applicability assessments
to a given building have been found to be deficient. Decisions to use prefabrication are still largely based on
anecdotal evidence or simply cost-based evaluation when comparing various construction methods. Holistic
criteria are needed to assist with the selection of an appropriate construction method in concrete buildings
during early project stages. Following a thorough literature review and comprehensive comparisons
between prefabrication and on-site construction method, a total of 33 sustainable performance criteria (SPC)
based on the triple bottom line and the requirements of different project stakeholders were identified. A
survey of U.S. experienced practitioners including clients/developers, engineers, contractors, and precast
concrete manufacturers was conducted to capture their perceptions on the importance of the criteria. The
ranking analysis of survey results shows that social awareness and environmental concerns were considered
as increasingly important in construction method selections. Factor analysis reveals that these SPCs can be
grouped into seven dimensions, namely, economic factors: “long-term cost,” “constructability,” “quality,”
and “first cost”; social factors: “impact on health and community,” “architectural impact”; and environmental
factor: “environmental impact.” The resultant list of SPCs provides team members a new way to select a
construction method, thereby facilitating the sustainable development of built environment.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
With heightened awareness of environmental pollution, natural
resource depletion and accompanying social problems, sustainable
development and sustainable construction have become a growing
concern throughout the world. Buildings are one of the heaviest
consumers of natural resources and account for a significant portion of
the greenhouse gas emissions. In the U.S., buildings account for 38.9% of
primary energy use, 38% of all carbon dioxide emissions, and 30% of
waste output [1]. Conventional on-site construction methods have long
beencriticized for low productivity, poor quality and safety records, long
construction time, and large quantities of waste in the industry.
Prefabrication is a manufacturing process, generally taking place at a
specialized facility, with which various materials are joined to form a
component part of the final installation [2]. Several benefits of applying
prefabrication technology in construction were commonly discussed in
previous literature [3–15], including: shortened construction time,
lower overall construction cost, improved quality, enhanced durability,
better architectural appearance, enhanced occupational health and
safety, material conservation, less construction site waste, less environ-
mental emissions, and reduction of energy and water consumption.
These advantages provide opportunities for prefabrication to better
serve sustainable building projects. Worldwide, the highest precast
levels in 1996 were located in Denmark (43%), the Netherlands (40%),
Sweden and Germany (31%) [16]. In the United States, the share of
reinforced concrete construction supplied by precast producers is only
6% while the average across the European Union is 18% [8]. Although the
U.S. precast concrete industry produces technologically and architec-
turally complex buildings and building elements, such as double tees,
hollow-core slab elements, inverted tee and ledger beams, and facade
panels, in building construction market, the percentage of precast
concrete systems is pretty low (approximately 1.2%) [7,8]. It is more
urgent to address prefabrication issues in concrete buildings while
achieving sustainable construction in the United States.
Pasquire and Connolly demonstrated that decisions to use prefab-
rication are still largely based on anecdotal evidence rather than
rigorous data, as no formal measurement criteria or strategies are
available [17]. Blismas et al. also indicated that holistic and methodical
assessments of the prefabrication applicability to a particular project
Automation in Construction 19 (2010) 235–244
⁎ Corresponding author. Tel.: +1 814 863 2079; fax: +1 814 863 4789.
E-mail addresses: 09chenying09@gmail.com (Y. Chen), gek3@engr.psu.edu
(G.E. Okudan), driley@engr.psu.edu (D.R. Riley).
0926-5805/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.autcon.2009.10.004
Contents lists available at ScienceDirect
Automation in Construction
journal homepage: www.elsevier.com/locate/autcon
http://www.usgbc.org/DisplayPage.aspx?CMSPageID=1718
mailto:09chenying09@gmail.com
mailto:gek3@engr.psu.edu
mailto:driley@engr.psu.edu
http://dx.doi.org/10.1016/j.autcon.2009.10.004
http://www.sciencedirect.com/science/journal/09265805
have been found to be deficient, and common methods of evaluation
simply take material, labor and transportation costs into account when
comparing various construction methods, without explicit regard for
the long-term cost or soft issues, such as life cycle cost, health and safety,
effects on energy consumption, and environmental impact of a project
[10]. Additionally, for individual building projects, prefabrication
technology is not always the only available option, nor is it always
better than on-site construction method due to various project
characteristics and available resources. If not employed appropriately,
change orders, severe delays in production, erection schedules,
substantial cost overruns, and constructability problems may be
encountered in the use of precast concrete systems. All of these
demonstrate that criteria for decisions regarding construction methods
are unclear and unrecorded. There is a need to establish holistic criteria
to select an appropriate construction method and stimulate the suitable
use of prefabrication for a given building project.
In this research, two prominent methods in building construction
are reviewed and discussed: the conventional on-site reinforced
concrete construction method, and the precast concrete building
method. In the sections that follow, the former method is referred as
the ‘on-site’ construction method, and the latter the ‘prefabrication’
method. The main objective of the research was to develop a holistic
sustainable performance criteria (SPC) set to assist design team
members in the selection of appropriate construction methods in
concrete buildings during early project stages. These criteria enable
applications of IT to support and automate the complex considera-
tions of prefabrication on concrete building projects. As a result, the
likelihood of sustainable construction is enhanced, both to meet
society’s environmental goals and account for the social and economic
impacts of the project.
2. Research methodology
Methodology selected for this research comprised of a question-
naire design, a questionnaire survey and interviews of the U.S.
construction industry practitioners, and a statistical analysis of the
survey data. Fig. 1 illustrates the methodology for the research.
2.1. Questionnaire design
A wide scope review of literature revealed that there was no
comprehensive list of performance criteria developed specifically for
construction method selection in concrete buildings. To compile a
meaningful list of criteria, several researches in related areas were
conducted. To ensure that prefabrication and on-site construction
method are clearly distinguishable by the selected criteria, the
comparison between the two methods was thoroughly explored.
Combined with sustainable concerns and requirements of project
stakeholders on construction method selection, a list of initial criteria
was developed.
Based on the derived criteria, an industry questionnaire survey
was designed by Adobe Livecycle Designer, which enables user to
create dynamic and interactive forms that are filled out on a
computer. The survey, which consisted of two main parts, aims at
investigating the perspective of the construction industry on the
importance of the criteria. Part one sought background information
about the respondents and their organizations, such as the experience
of the respondent in the construction industry, and the number of
projects using prefabrication the respondent has been involved in. In
part two, respondents were asked to rate the level of importance of
the derived criteria based on a scale of 1–5, where 1 is ‘least
important’, 2 ‘fairly important’, 3 ‘important’, 4 ‘very important’, and 5
‘extremely important’. To ensure a better understanding of the
criteria, definition of each criterion was clarified and guidance on
completion was given in the questionnaire. At the same time,
respondents were encouraged to provide supplementary criteria
that they consider to influence construction method selections but
were not listed in the provided questionnaire (refer to Appendix A for
questionnaire details).
2.2. Questionnaire survey
A pilot survey was conducted with experienced contractors and
engineers to validate the final questionnaire. The questionnaire was
then administered by email to 412 selected industry practitioners
within the U.S. construction industry who are primary participants in
the precast concrete supply chain, including construction clients/
developers, engineers, contractors, and precast concrete manufac-
turers. All of them have different opinions and focus on construction
method selection. Obtaining views from the four categories ensures a
holistic criteria set for construction method selection.
Survey questionnaires were emailed to 84 construction clients/
developers, 71 engineers, 145 contractors, and 112 precast concrete
manufactures in the United States. The email addresses of precast
manufactures were obtained from the PCI’s (Precast/Prestressed
Concrete Institute) Membership Directory [18] and NPCA’s (National
Precast Concrete Association) Membership Directory [19] by selecting
manufacturers who produce architectural precast units, such as
architectural beams, facades, slabs, and stairs. Contact information
for the construction clients/developers, engineers, and contractors
were obtained from the Partnership for Achieving Construction
Excellence (PACE) database. PACE is based in the Department of
Architectural Engineering at The Pennsylvania State University and is
a working partnership between Penn State students, faculty, and
building industry practitioners. The developers, engineers, and
contractors for the survey were selected from those who had worked
on building projects and also had experience in prefabrication.
To gain further understanding of the survey results, five selected
respondents who had rich experience in concrete prefabrication and
construction method selection process were interviewed after
returning survey responses. Specifically, they were asked how they
considered their selections, such as why some criteria are less or more
important than others etc.
Fig. 1. Research framework and methodology.
236 Y. Chen et al. / Automation in Construction 19 (2010) 235–244
http://www.pci.org
http://isiarticles.com/article/67839
R E S E A R C H A N D A N A LY S I S
Construction Matters
Comparing Environmental Impacts of Building Modular and
Conventional Homes in the United States
John Quale, Matthew J. Eckelman, Kyle W. Williams, Greg Sloditskie,
and Julie B. Zimmerman
Keywords:
environmental impact assessment
industrial ecology
life cycle assessment (LCA
)
modular building
off-site construction
residential homes
Summary
Modular construction practices are used in many countries as an alternative to conventional
on-site construction for residential homes. While modular home construction has certain
advantages in terms of material and time efficiency, it requires a different infrastructure than
conventional home construction, and the overall environmental trade-offs between the two
methods have been unclear. This study uses life cycle assessment to quantify the environ-
mental impacts of constructing a typical residential home using the two methods, based on
data from several modular construction companies and conventional homebuilders. The
study includes impacts from material production and transport, off-site and on-site energy
use, worker transport, and waste management. For all categories considered, the average
impacts of building the home are less for modular construction than for conventional con-
struction, although these averages obscure significant variation among the individual projects
and companies.
Introduction
In the United States, buildings represent the largest single
end-use of energy and emitter of greenhouse gases (GHGs).
Quantitatively, buildings account for 40% of energy use in the
United States and a comparatively significant proportion else-
where (Pérez-Lombard et al. 2008; DOE 2008). Energy and
materials are used, and corresponding environmental impacts
incurred, in large quantities throughout the life cycle of a build-
ing. There has been significant life cycle assessment (LCA)
research dedicated to identifying which materials and building
components are the largest contributors to various environ-
mental impacts (Ortiz et al. 2009); however, the process of
Address correspondence to: Matthew J. Eckelman, Department of Civil & Environmental Engineering, Northeastern University, 360 Huntington Ave., Boston, MA, USA
02115. Email: m.eckelman@neu.edu
c© 2012 by Yale University
DOI: 10.1111/j.1530-9290.2011.00424.x
Volume 16, Number 2
conducting an LCA on buildings is complicated. Factors such
as site specifications, thousands of potential components and
material types, and various construction assembly techniques
(Priemus 2005), as well as the highly decentralized nature of
the industry, make it very difficult to track down the neces-
sary data and produce meaningful, generalizable results (Kohler
and Moffatt 2003; Malin 2005; Sharrard 2007). Nevertheless,
lessons learned from various LCAs are broadly applicable and
it is clear that LCA is a useful and even necessary component
of a holistic and integrated green building design process (Ortiz
et al. 2009).
It is well established that the largest proportion of envi-
ronmental impacts associated with buildings is related to the
www.wileyonlinelibrary.com/journal/jie Journal of Industrial Ecology 243
R E S E A R C H A N D A N A LY S I S
occupancy or use stage of the life cycle (Adalberth 1997;
Scheuer et al. 2003). For example, energy used for heating,
cooling, lighting, equipment, and appliances typically far out-
weighs the energy demand of other life cycle stages, such as
construction and the production of building materials. These
proportions will likely change with time as building designs and
operations improve in terms of energy and material efficiencies.
Full implementation of current design strategies and technolo-
gies could see the proportion of impacts associated with the
occupancy phase fall sharply. As this happens, the relative im-
portance of other life cycle stages such as construction will be
greater. This point is illustrated by a recent study of Gustavs-
son and Joelsson (2010), who show that in an optimally energy
efficient building, the phases of material production and con-
struction account for 60% of life cycle energy consumption. As
such, it is necessary also to begin developing and evaluating
strategies to reduce the impacts associated with these stages of
the building life cycle.
Modular building is one promising technique to lower the
impacts of construction and is utilized for various building types,
including single-family homes, multifamily housing, hotels, dor-
mitories, and various commercial and retail structures. Modu-
lar construction is a form of prefabrication that involves the
creation of discrete volumetric sections of buildings that are
transported to a site and assembled into a complete building.
The modules are produced off-site in a factory environment
without exposure to weather. Panel systems are a related off-
site construction technique, where individual wall sections are
manufactured without factory assembly into volumetric mod-
ules. Unlike in panelized or component-based methods of pre-
fabrication, in modular construction most of the interior and
exterior finishes are put into place in the factory. The modules
are transported to the building site 80% to 90% complete, where
they are assembled and finished. Because the modules can be
constructed while the site and foundation are being prepared,
instead of after, modular construction is thought to reduce con-
struction times by 30% to 50% (Smith 2010). Modular compa-
nies may also economize on costs by producing several modules
in parallel, reducing worker and machinery transportation, and
engaging in bulk material ordering.
Residential modular buildings are different than trailers or
“double-wide” homes, which are defined as “manufactured hous-
ing” by the federal government. Trailers have a permanent steel
frame built into the floor structure, and can be relocated. Con-
sidered temporary buildings because they are transportable, they
are built to federal building requirements known as the HUD
(U.S. Department of Housing and Urban Development) code,
and are financed like a vehicle. Unlike site-built or modular
homes, they also tend to depreciate in value. However, mod-
ular houses are built to local and state building codes, in the
same way as a site-built house, and those codes are typically
more restrictive than the HUD code on energy and durability
issues. A modular house is of equal quality to a site-built home
because the materials are exactly the same for the same design,
with the exception of added structure to ensure the modular
house can be transported without being damaged.
The size of the modular industry nationally in the United
States is approximately 2% to 3% of residential construction,
with wide variation among regions. In the Northeast, nearly
6% of new homes utilize modular techniques, while the pro-
portion in the West is less than 1%. The broader category of
prefabricated construction (modular, manufactured, and panel-
ized homes) represents more than 25% of the total (Hallahan
Associates 2011).
Some aspects of modular home construction are identical
to conventional practices, such as site preparation, excavation,
and installation of the foundation, but there are many impor-
tant differences. While building homes in a factory can require
additional lighting, heating, or water use in addition to the en-
ergy associated with transporting the modules, there are also
opportunities for benefits in terms of material and energy effi-
ciencies. As such, the environmental trade-offs between mod-
ular building and conventional on-site construction have not
been thoroughly investigated.
Accordingly, the aim of this study is to compare these two
methods of building construction using LCA. The analysis is
based on data from several modular and on-site building projects
in the mid-Atlantic United States and focuses on the dif-
ferences between the two construction techniques, covering
production and transport of building materials, construction
processes, worker transport to the job site and/or factory, and
construction waste management. Although panelized construc-
tion is more popular in some parts of the United States and
Europe, this report focuses on modular prefabrication. This is
a cradle-to-gate study that considers only the materials pro-
duction, transport, and construction phases of the building life
cycle. There are potential differences in the use phase between
homes constructed using modular and conventional techniques,
due to envelope tightness, for example, but such effects are
highly variable and were not included in this construction-
focused study.
Life Cycle Assessment Research
on Buildings and Construction
Researchers have used LCAs to examine many aspects of
buildings and construction. The majority of these studies have
analyzed energy consumption and, to a lesser extent, global
warming (Ortiz et al. 2009), whereas very few have addressed
other environmental concerns such as loss of habitat or emis-
sions of toxic substances. One line of inquiry has focused on the
impacts of material or design choices in the life cycle of build-
ings using process-based LCA. An early comparison of wood,
steel, and concrete office buildings conducted by Cole and Ker-
nan (1996) quantified life cycle energy use and found little
difference in impact between the different material structural
systems, especially on the scale of the entire life cycle. Keoleian
and colleagues (2000) considered GHG emissions as well in a
study of a residential home in Michigan, analyzing the life cycle
gains and losses from several green building options. Itard and
Klunder (2007) compared the life cycle embodied materials,
energy, and water use among four different options of building
244 Journal of Industrial Ecology
R E S E A R C H A N D A N A LY S I S
renovation ranging from simple maintenance to complete
demolition and rebuilding. They found that although demo-
lition and rebuilding have large impacts in terms of embodied
materials, the lower use phase energy and water impacts of a new
building mean that there are large trade-offs to be considered.
Another collection of LCA building studies has used economic
input–output life cycle assessment (EIO-LCA) or hybrid anal-
yses to model economy-wide life cycle impacts of a building, or
a subset of building materials and components, again typically
considering energy and emissions of GHGs (Bilec et al. 2006;
Ochoa et al. 2002; Treolar et al. 2000).
A number of building construction LCA studies have ana-
lyzed environmental impacts other than energy use and GHG
emissions. Scheuer and colleagues (2003) completed one of the
most comprehensive process-based LCAs for an institutional
building, finding that impacts of global warming, ozone deple-
tion, eutrophication, and acidification potentials followed the
same basic pattern as energy use where the use phase of the
building was the dominant source. The only impact category
that approached parity between the use phase and other life cy-
cle stages was waste production, with material production and
construction accounting for approximately 28%, as compared
to 65% generated during the use phase (Scheuer et al. 2003).
Guggemos and Horvath (2005) found that the construction
phase accounted for only 2% of energy consumption and 1% of
GHG emissions, but 7% of carbon monoxide (CO) emissions,
8% of nitrogen oxides (NOx) emissions, and 8% of particulate
matter (PM) emissions. In some cases, the construction phase
was found to contribute the majority of impacts for certain
impact categories. For example, Ochoa and colleagues (2002)
found that the construction phase contributes 57% of toxic air
emissions and 51% of hazardous waste generated over the build-
ing life cycle. Similarly, Junnila and Horvath (2003) found that
the impacts of producing the building materials dominated the
release of toxic metals to the environment and also contributed
significantly to smog-forming emissions.
In summary, the literature to date suggests that the use or
occupancy phase tends to dominate most environmental im-
pacts over the life cycle of a building, especially for energy use
and GHG emissions, with some exceptions for other impact
categories. However, another significant conclusion is that the
construction phase is the next most important area in terms of
impacts, and therefore the potential for reducing the environ-
mental burden of buildings. For example, while the occupancy
phase is reported to account for anywhere from 70% to 98%
of building energy use (Ortiz et al. 2009), the construction
phase has been found to account for 2% to 26%, depending
on the reference building’s design and intended use (Adalberth
1997; Cole 1998; Cole and Kernan 1996; Keoleian et al. 2000;
Oregon Department of Environmental Quality 2010; Scheuer
et al. 2003).
There are many potential sources of construction phase im-
pacts that are discussed. Gangolells and colleagues (2009) found
that transportation and construction equipment, waste produc-
tion, and water consumption all had significant environmental
consequences, implying that any improvements in these areas
could be priority targets for reducing the overall life cycle im-
pact of the building. Bilec and colleagues (2006) similarly found
for a concrete parking structure that the transportation of con-
crete to the site, particularly for the precast pieces, was the most
significant construction process. Likewise, Guggemos and Hor-
vath (2005) found that within the construction phase, work on
the structural frame had the largest impacts, mostly due to the
heavy use of diesel equipment, a finding that was corroborated
by Junnila and Horvath (2003).
Very few researchers have attempted to analyze the impact
of the method of construction. In particular, there is little dis-
cussion of the implications of off-site construction as opposed
to typical site-built construction. Kim (2008) compared life
cycle impacts of a modular and a conventionally constructed
home in Michigan, analyzing energy use, material consumption,
GHG emissions, and waste generation. This work suggested that
solid waste generation, transportation energy, and GHG emis-
sions are significantly lower when modular construction is used.
For example, solid waste generation was found to be 2.5 times
greater for the on-site construction process. However, this study
focused on a single building and relied on several general as-
sumptions to fill gaps in empirical data. Another relevant study
was carried out in northern Japan by Nishioka and colleagues
(2000), who considered the environmental trade-offs in ver-
tically integrated factory-built housing, which required more
materials than a typical home but also performed better. The
authors found that the energy and carbon debts incurred by the
additional materials were paid off through efficiency gains in
less than six years, well below the average lifetime of homes in
that area.
With increasing interest in the environmental profile of con-
struction and green buildings generally, the lack of quantitative
assessment work on modular construction is an important omis-
sion in the existing literature. In addition to environmental
considerations, stakeholders from industry and government are
also interested in the relationship between modular construc-
tion and the affordability and availability of homes (Britto et al.
2007; Diez et al. 2007).
Methodology
The first step of the project was to collect construction data
for both off-site and on-site construction methods. Three resi-
dential modular companies, generally representative of the east-
ern U.S. modular industry, supplied data on completed projects
for this study, including utility bills, worker commuting infor-
mation, building materials and waste procedures, construction
schedules, employee schedules, and other relevant information.
As most data were reported as an amount per week or year, an-
nual production estimates for each modular building factory
were used to scale the information to the common functional
unit of a 2,000 square foot (sq ft, or 186 square meters [m2]),
1
two-story home that is a model for one of the companies in-
volved in the study (figure 1).
As noted in previous studies (Kim 2008), it is difficult
to identify instances where two versions of the exact same
Quale et al., Construction Matters: LC A of Modular Buildings 245
R E S E A R C H A N D A N A LY S I S
Figure 1 Elevations for the functional unit of a 2,000 square foot, two-story production model.
building have been completed using on-site and modular con-
struction, making it unfeasible to make comparisons based on
actual projects. Therefore it is necessary to use proxy data for
one or the other method of construction in order to compare
the environmental impacts of building a common functional
unit. Other authors have used construction cost estimators for
on-site construction processes (Bilec 2006; Kim 2008), which
do not directly yield environmentally relevant information, but
can be used in combination with EIO-LCA.
Here we estimate material and energy use data by compiling
thorough construction specifications for the modular building
shown in figure 1 and then surveying a random sample of five
experienced on-site professional homebuilders in the sales re-
gion of the modular building companies. The homebuilders
were asked to assume they were building the home on-site at a
lot in their region. They were selected because they had recent
experience constructing buildings of the same size and type.
The survey covered the general steps required to construct the
building, from site preparation through final cleanup. These pro-
fessionals were provided complete drawings and specifications
of the modular building to estimate the construction schedule,
equipment and energy needs, and the required number of staff
and subcontractors, including their commuting information.
The survey results provided the necessary data for the analysis
of on-site construction.
For modular construction, a two-story modular residence
can be visualized as consisting of four boxes: A, B, C, and D.
Boxes A and B sit side by side and make up the ground floor,
while C and D sit side by side on top of A and B and form
the second floor. Due to restrictions on shipping dimensions on
public roads, it is not possible to build the house depicted in
figure 1 with any fewer than four separate modular pieces. Each
of the four pieces that make up this house must have a top,
bottom, and four sides in order to ensure structural integrity
during shipment and installation. This means, however, that in
a modular house there is the possibility of a number of redundant
walls and floors. For the modular house design used in this
fold up roof
module A module B
module C module D
foundation
structure required
for both modular
and conventional
construction
structure required
for modular
construction only;
this structure can
be temporary
Figure 2 Schematic diagram of a four-module residential building,
showing redundant structure. The sections below detail the
assumptions and parameters of each building life cycle phase
considered in the study: materials production, materials transport,
worker transport, construction processes (in factory and on-site),
and waste management. A detailed list of material and energy inputs
for each mode of construction is given in table 1.
study, there are two sets of wall studs between boxes A and B
(and between boxes C and D), creating two redundant vertical
surfaces. There is also both a ceiling for box A and a separate
floor for box C (and between boxes B and D) resulting in two
redundant horizontal surfaces (figure 2). The added material
for the redundant structure was not present for the site-built
version of the home in this analysis.
Materials Production
In comparing the modular and on-site methods, only those
building materials whose amounts differed between construc-
tion methods were considered. For example, dimensional lum-
ber for wall framing was included, while doors and windows,
which appear identically in both versions of the building, were
not. Material types and quantities came from both bills of ma-
terials and estimates based on the construction drawings for
246 Journal of Industrial Ecology
R E S E A R C H A N D A N A LY S I S
Table 1 Inputs of materials and energy for modular and site-built versions of the home functional unit (only those inputs that differ
appreciably between construction methods are shown)
Construction method
Unit Modular Conventional
Material
Wood (marriage walls) lb 3,190 0
Wood wastage lb 0 3,300
Drywall wastage lb 1,380–1,600 2,200
Material transport
Building materials: 16 metric ton truck miles 110–480 110–1,600
Building materials: 28 metric ton truck miles 30–290 110–290
Modules to site: 28 metric ton truck miles 1,200 0
Worker transport
To factory: car/light duty truck miles 2,500–13,000 0
To site: car/light duty truck miles 1,000–3,500 7,800–26,000
Energy use
Electricity off-site MWh 2.0–7.2 0
Electricity on-site MWh 0.1 0.5–1.6
Gasoline (equipment) MMBTU 24 15–54
Fuel oil (heating off-site) MMBTU 24 0
Propane (heating off-site) MMBTU 0.4 0
Natural gas (heating off-site) MMBTU 0.7 0
Natural gas (heating on-site) MMBTU 10–18 85–145
Waste management
Mixed materials lb 4,580 5,500
Notes: lb = pounds; MWh = megawatt hours; MMBTU = million British thermal units (Btu).
the building (figure 1). Based on surveys of contractors, it was
determined that the foundation and roof structure would not
appreciably differ between the two construction methods.
There are two important differences in the material require-
ments of modular and on-site construction projects that were
incorporated in this analysis. First is the amount of material
that gets incorporated into the structure. As noted above, the
marriage walls required for transporting and then joining the
modules add nearly 25% to the mass of wood in the building.
The second major difference in material requirements between
the two construction methods is related to waste, as this rep-
resents extra building materials that must be ordered to com-
plete the home functional unit. In general, modular residential
companies build many homes at once and order materials and
products as needed for the efficient use of time and the factory’s
material storage space. Many modular building companies also
purchase dimensional lumber and other materials cut to spec-
ifications, or make cuts using digital fabrication equipment,
resulting in fewer off-cuts, and therefore requiring less over-
ordering to make up for wastage. Small pieces can be saved for
future projects, such as wood used for blocking. The general
policy not to begin construction on a modular home until all
materials have been procured also reduces over-ordering and
impacts associated with multiple deliveries.
In contrast, on-site homebuilders typically order materials
and products for one building at a time (for the purposes of this
study the surveyed homebuilders assumed the lot was discrete
and not part of a larger housing development), and may make
many ad hoc trips to building supply stores to procure materials
as needed. Conventional homebuilders generally lack sufficient
dry or climate-controlled storage space at the construction site
to store building materials and have fewer staff to determine
efficient procurement strategies. The homebuilders surveyed
for this study agreed that an “order as you go” strategy is less
efficient and can also lead to additional material and employee
transportation impacts. There is anecdotal evidence that on-
site builders routinely order a surplus of 5% to 15% to make
up for wasted material. Kim (2008) assumed a wastage rate of
5% across all material types, but it is more likely that the rate
varies significantly across materials. This rate is quite difficult
to track, however, with subcontractors managing some waste
streams (such as plumbers keeping copper pipe cuts) out of the
purview of the general contractor.
A survey of modular construction facilities revealed that
practically all building materials were reused, with the excep-
tion of some gypsum (0.7–0.8 pounds per square foot [lb/sq
ft]) and copper wire (0.03–0.1 lb/sq ft), which are imprac-
tical to use in small sections.2 These amounts were derived
from factory reports of waste generation, which were supplied
as a weekly or annual tally and then scaled to the 2,000 sq
ft functional unit. On-site construction over-ordering was as-
sumed to be equal to the generic wastage rate from residen-
tial construction of 4.4 lb/sq ft (EPA 2009). This was broken
down into constituent material types, specifically dimensional
Quale et al., Construction Matters: LC A of Modular Buildings 247
R E S E A R C H A N D A N A LY S I S
lumber (1.7 lb/sq ft) and gypsum wallboard (1.1 lb/sq ft), based
on the proportions reported in characterization studies of con-
struction waste (DSM Environmental Services 2008; NAHM
1997).
The top section of table 1 shows the net differences in
material requirements for the two construction methods, cov-
ering both structural redundancy and material efficiency, in-
cluding dimensional lumber, drywall, and masonry. Those
materials types that are not expected to significantly differ in
quantity between the two construction methods, including sid-
ing, roofing materials, metal piping and wiring, carpets, fixtures,
tiles, packaging cardboard, and others, are not considered in the
comparison.
Material Transport
For conventional on-site construction, transportation im-
pacts of only those additional materials needed beyond those
required for modular construction were considered (table 1).
The remaining majority of building materials were excluded, as
the impacts of transporting these from distributors to the site
was assumed to be the same as transporting them from distrib-
utors to the modular building factories. An average distance of
30 miles3 from material distributors to the construction site and
from the site to the local construction and demolition (C&D)
waste management facility was assumed for all materials, which
is similar to transport distances reported in the work of Kim
(2008). The transport of waste from modular and conventional
construction sites was also considered. The vehicle used for all
material transportation was modeled as an average large cargo
truck with empty backhauling.
For modular construction, materials are transported to the
factory and then the modules themselves need to be transported
to the building site. Transport requirements for the finished
modules were calculated using the weight of the modules (four
modules each weighing approximately 10 metric tons (t)4 for
a 2,000 sq ft home) and the average shipping distance for the
modular companies who participated in the study, which was
estimated to be 300 mi.
Worker Transport
For on-site construction, worker transport was calculated
based on data supplied in the homebuilder survey (see table 1).
For each task (interior painting, for example), each respondent
was asked to estimate the number of people needed, the number
of days to finish the task, and city of origin of those workers.
Round-trip commuting distances were calculated as
Off-site worker-miles
= Round-trip distance × People needed for task
× Duration of task in days × 1.5.
The 50% factor of safety was determined from contractor
interviews, as surveys indicated that scheduling delays or tasks
that must be repeated are commonplace during on-site con-
struction projects. For example, the plumbing subcontractor
may arrive prior to completion by the framing subcontractors
or the inspector must make multiple trips to permit various as-
pects of the project. This parameter is considered later in the
uncertainty analysis. All on-site worker miles were modeled as
small-truck transport, except in the cases where large equip-
ment or material was being delivered (such as an excavator for
site preparation or a cement truck). In these cases, larger truck
sizes were assigned as appropriate and the trucks were assumed
to be loaded to 50% of capacity for those miles.
In the case of modular construction, worker transport to the
facility was determined using data on where employees live in
relation to the factory and the number of workdays per year.
Transportation and craning of the modules were also assessed.
With the actual commuting distance of each employee, weekly
days of work, and an assumption of 50 working weeks a year,
total annual worker miles were calculated as
Off-site worker-miles
= Round-trip distance × Number of employees
×Workdays/week × 50 weeks.
Using annual production of a factory in total square feet of
built area, a normalized worker transport metric was determined
for each company, which was then scaled to the functional unit
of a 2,000 sq ft building. It was assumed that miles driven
by workers at modular factories were 50% by small car and
50% by van or truck, based on conversations with the modular
companies and photographs of their parking lots.
Energy Use During Construction
Data on the energy used during on-site construction also
came from the homebuilder surveys (see table 1). For each task,
the respondent was asked to give the electric- or diesel-powered
equipment that would typically be used during the construction
task and the duration of use. Average fuel or electricity use for
each appliance or piece of machinery came from the U.S. federal
government’s Energy Star program (EPA 2011) and technical
specifications from manufacturers. Energy use calculations com-
bined the per hour energy usage with assumed usage per day and
days for the task as
Energy use
= Hourly energy use × Hours per day used × Days per task.
Energy used by vehicles and generators was recorded as diesel
in machinery with a gross heating value of 45 megajoules per
kilogram (MJ/kg).5 Electricity used by tools and other electri-
cal equipment was recorded as kilowatt-hours (kWh) of low-
voltage electricity in the eastern connect of the U.S. grid, in-
cluding transformation and distribution losses and using gross
primary energy heating values, from the U.S. Life Cycle Inven-
tory database (NREL 2011).
A number of assumptions were made regarding how often
equipment was used to ensure a consistent methodology across
the different homebuilders. For office equipment used in the
general contractor’s office, daily use was assumed to be only
248 Journal of Industrial Ecology
R E S E A R C H A N D A N A LY S I S
Figure 3 Global warming potential from modular (Mod) and conventional (Conv) construction cases of a 2,000 square foot residential
home, in metric tons of carbon dioxide equivalents (CO2-eq); differences in construction only.
eight hours per day, although many pieces of equipment, such as
computers and printers, were reportedly left on overnight. It was
also assumed that the general contractor had an office for both
on-site and off-site construction cases, either as a mobile unit or
as dedicated office space in the modular building factory. For on-
site electricity use, it was assumed that a temporary power pole
was used (i.e., grid electricity) unless a stand-alone generator
was specified in the construction documents (for a concrete
vibrator or an air compressor, for example). If temporary lighting
was specified, it was assumed that one 100 watt (W) light per
worker would be used.
One source of energy use that was not explicitly covered
in the survey for the on-site projects is temporary heat on the
job site. Based on the experience of the research team on con-
struction sites and in further consultation with contractors, it
was assumed that in the mid-Atlantic region (where the on-site
contractors are based), 50% of an on-site construction schedule
requires temporary heat. Of that 50% of the schedule requir-
ing temporary heat, 30% requires continuous heat (to protect
interior finishes, for example).
Energy use in the modular factories was determined based
on energy bills provided by the companies. Annual fuel and
electricity use were calculated using average yearly energy ex-
penditures, scaled to the 2,000 sq ft building functional unit.
Waste Management
Modeling of waste management also considered, for com-
parative purposes only, the net differences in waste between
the two construction methods from table 1. All materials were
assumed to be sent to a C&D waste landfill.
Life Cycle Assessment Software
The life cycle inventory was compiled in SimaPro 7.3 LCA
software, relying on inventory data from the US-EI version
of the ecoinvent 2.2 and U.S. LCI databases, with complete
adaptation of all generic electricity unit processes to the U.S.
context. Data from the five categories described above were
entered as separate items for each of the three modular and
five on-site cases. Subsequent impact assessment was performed
using the Building for Environmental and Economic Sustain-
ability (BEES) 4.02 method, which was developed specifically
for the U.S. building sector (NIST 2007). This yielded impact
results for ten environmental impact categories: global warm-
ing; acidification; human health from cancer, non-cancer, and
criteria air pollutants; eutrophication; ecotoxicity; smog; water
intake; and ozone depletion.
Uncertainty
Several of the input parameters used here are significantly
uncertain and their associated error was calculated for each
factory and building site. Percent uncertainty was estimated
and propagated for on-site waste generation (±25%), transport
distances to the modular facility (±25%), on-site ad hoc trips
(±25%), and on-site temporary heating (±50%). Uncertainty
associated with the choice of emissions factors, the contractor
surveys, and human error in reporting is certainly present, but
is not considered here.
Results and Discussion
Figure 3 shows the LCA results for GHG emissions for the
three modular and five on-site companies, with averages de-
picted for each construction method. The analysis reveals that
impacts from modular construction are, on average, lower than
those from on-site construction, but that there is significant
variation within each. For example, Modular Company 1’s emis-
sions were significantly higher than the other two modular cases,
and also higher than one of the five on-site companies. This par-
ticular facility is located in a rural area with a commute that is
more than twice as long as for the other modular facilities, when
normalized for production volumes. This factory also reported
higher levels of electricity use than the others and was heated
with fuel oil, again leading to increased levels of emissions. On
Quale et al., Construction Matters: LC A of Modular Buildings 249
R E S E A R C H A N D A N A LY S I S
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N
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:
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ee
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se
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s;
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s;
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ol
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on
s;
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e
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ol
e
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s
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H
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);
D
A
L
Y
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sa
bi
li
ty
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ju
st
ed
li
fe
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ea
r;
N
=
n
it
ro
ge
n
;2
,4
–
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=
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di
ch
lo
ro
ph
en
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c
ac
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;N
O
x
=
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it
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ge
n
ox
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es
;C
FC
-1
1
=
tr
ic
h
lo
ro
flu
or
om
et
h
an
e.
O
n
e
ki
lo
gr
am
(k
g,
S
I)
=
10
3
gr
am
s
(g
)
=
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6
m
il
li
gr
am
s
(m
g)
≈
2.
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4
po
un
ds
(l
b)
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n
e
li
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r
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)
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(m
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,S
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≈
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26
4
ga
ll
on
s
(g
al
).
250 Journal of Industrial Ecology
R E S E A R C H A N D A N A LY S I S
average, however, GHG emissions from conventional construc-
tion were about 40% higher than for modular construction.
Given that the production and transport of several building
materials were omitted from the analysis, as they were iden-
tical between construction methods, it is more appropriate to
consider the absolute rather than relative difference in GHG
emissions, which were found here to be nearly six metric tons
of carbon dioxide equivalents (CO2-eq) higher for on-site con-
struction, per 2,000 sq ft home.6 It is important to note again
that this difference is likely to be modest compared to the
emissions associated with building occupancy, but also that the
relative importance of construction impacts will increase as the
use of buildings becomes more efficient.
Differences in the materials needed for the two construc-
tion methods did not significantly affect results, largely due to
the fact that the additional dimensional lumber needed to give
structural support to the modular panels during transport was
nearly equal to the extra lumber needed to make up for wood
scraps generated during on-site construction. Material transport
and waste management were also small contributors to overall
GHG emissions. Energy use on-site and worker transport to the
site were the most important categories for GHG emissions from
conventional construction, which is intuitive as both represent
direct combustion of fossil fuels. Therefore, reducing unneces-
sary worker trips, idling of equipment, and temporary heating
through effective management practices remain the most im-
portant goals of low-carbon construction of homes.
Uncertainty associated with selected input parameters is
shown by the error bars of figure 3. There is moderate overlap
between the sets of modular and conventionally built homes,
and a much larger uncertainty range for the latter set, which
reflects the sensitivity of the overall results to assumptions of
temporary heating and redundant worker trips.
Table 2 shows impacts from each construction stage for the
other impact assessment categories included in the BEES 4.02
methodology. The distribution of impacts among construction
processes for most other impact categories is similar to that
of GHG emissions: on-site construction has moderately higher
impacts (20% to 70%) than modular construction, with factory
and on-site energy use being the primary drivers of impacts. The
exceptions to this trend are eutrophication and water intake,
which are higher for modular construction due to the greater
use of electricity, and ozone depletion, which is several times
higher for conventional construction, due to the production and
refining of crude oil needed for vehicles transporting workers
and materials to the job site. This surprising result is not at all
intuitive and underscores the importance of using system-level
analysis tools such as LCA, as the environmental differences
between two products may be due to processes far up the supply
chain.
As seen in the summary rows of table 2, modular construc-
tion has fewer impacts, on average, than on-site construction for
all environmental impact categories, although again the uncer-
tainty associated with these values is significant. Examining the
three individual modular and five on-site homes individually,
the Mod1 home has high impacts relative to the other modular
homes, stemming in part from its rural location, as explained
above. The Conv2 home has low impacts relative to the set of
conventional homes. In this particular case, the contractor who
supplied the information in the study worked with a local crew
and so reported relatively short distances for worker transport
to the construction site, which is a major driver of impacts for
most categories. This contractor also reported lower consump-
tion of all fuels and electricity on-site than reported by other
contractors. The variability of the responses serves to highlight
the site- and company-specific nature of this study, as well as the
potential for error in drawing general conclusions from single
building case studies.
The environmental benefits of a compressed construction
schedule for modular construction are implicit in the model
inputs, as they were scaled to annual production volumes, but
still bear discussion. This analysis assumes energy inputs av-
eraged over the year; however, location and time of year will
significantly affect the results for each of the two construc-
tion methods, particularly as they will determine the number
of heating-degree days needed both for the modular factory and
for temporary on-site heating.
While this study has focused on residential construction,
there are modular buildings in the commercial building sec-
tor as well. Commercial buildings tend to have more energy-
intensive structural materials (steel and concrete, as opposed
to wood), therefore the additional structural material required
for modular construction may have a more significant impact
than for the single-family homes considered here. In addition,
there is greater variety in the percentages of construction com-
pleted off-site for commercial or institutional modular projects
compared to single-family residential projects.
Regardless of the environmental preferences shown here,
there is potential to improve environmental impacts in both
methods of construction. The main opportunities for im-
provement come in the energy for construction and worker
transportation categories. Based on field visits and anecdotal
evidence from the industry, many modular factories are the
equivalent of large warehouses with little, if any, insulation.
As these facilities must be heated or cooled throughout the
year for worker comfort, a significant amount of this energy
is wasted. For on-site homebuilders, implementation of best
practices for on-site energy use (such as no idling), better mate-
rial and equipment procurement policies, and implementation
of carpooling could likely give some improvement. In addi-
tion, it appears likely that homebuilders working on multiple
homes on adjacent lots are likely to find efficiencies in material
and employee transport compared to those working on discrete
lots.
Acknowledgements
This research was made possible through the generosity of
the many individuals in the companies that participated in the
study. Partial funding for this study was provided by the Modular
Building Institute, a commercial modular industry trade asso-
ciation. Additional direct and indirect funding was provided
Quale et al., Construction Matters: LC A of Modular Buildings 251
R E S E A R C H A N D A N A LY S I S
by the University of Virginia (UVa) School of Architecture.
UVa graduate students Rachel Lau and Emily McDermott con-
tributed to the research and editing.
Notes
1. One square foot (ft2) ≈ 0.093 square meter (m2, SI).
2. One pound per square foot (lb/ft2) ≈ 4.88 kilograms per square
meter (kg/m2).
3. One mile (mi) ≈ 1.609 kilometers (km, SI).
4. One metric ton (t) = 103 kilograms (kg, SI) ≈ 1.102 short tons.
5. One megajoule per kilogram (MJ/kg) ≈ 429.9 British thermal units
per pound (Btu/lb).
6. CO2-eq: Carbon dioxide equivalent (CO2-eq) is a measure for de-
scribing the climate-forcing strength of a quantity of greenhouse
gases using the functionally equivalent amount of carbon dioxide as
the reference.
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About the Authors
John Quale is an associate professor at the University of
Virginia School of Architecture, Charlottesville, VA, USA,
where he directs the Graduate Architecture program. Matthew
Eckelman is an assistant professor in the Department of Civil
& Environmental Engineering at Northeastern University,
Boston, MA, USA. Kyle Williams was a masters student at
the School of Forestry and Environmental Studies at Yale
University at the time of writing, and is currently enrolled
in the Stanford Design Program, Stanford, CA, USA. Greg
Sloditskie is a principal at MBS Consulting, Inc., a consul-
tancy focused on modular buildings, located in New York,
NY, USA and West Milton, PA, USA. Julie Zimmerman is
an associate professor in the Department of Chemical & En-
vironmental Engineering and the School of Forestry & En-
vironmental Studies at Yale University, New Haven, CT,
USA.
Quale et al., Construction Matters: LC A of Modular Buildings 253
United States Patent (19)
Haug
54
MODULAR CONSTRUCTION ELEMENT
Merrill W. Haug, 815 O’Farrell St.,
San Francisco, Calif. 94109
(22 Filed: Oct. 29, 1974
(21) Appl. No.: 518,344
76) Inventor:
52 U.S. Cl………………. 248/188.1; 46/30; 248/1
6
5
(51) Int. Cl’………………………………….. F16M 11/
20
58) Field of Search…………….. 248/188. 1, 165,346;
46/16, 17, 21, 22, 23, 30, 25; D6/85, 145;
D19/61; D30/10; 52/DIG.
10
(56) References Cited
UNITED STATES PATENTS
2,902,821 9/1959 Kelly………………………………… 46/
30
3,310,906 3/1967 Glukes……………………………… 46117
3,537,706 1 1/1970 Heavener………………………….. 46/30
3,564,758 2/1971 Willis………. 46/
25
3,698,124 10/1972 Reitza et al…. 46/30
D74,395 211928 Silberhartz…………….. … D30/10
Dl 11,853 10, 1938 Johnson…………………………. D 1916.1
[11] 3,940,100
(45) Feb. 24, 1976
D212,267 9/1968 Dreyfuss………………………… D6/1
45
Primary Examiner-William H. Schultz
Assistant Examiner-Robert A. Hafer
Attorney, Agent, or Firm-Limbach, Limbach &
Sutton
57 ABSTRACT
A modular element for constructing furniture or artis
tic sculptures comprising a flat member having three
equilaterally arranged legs and three equilaterally ar
ranged, arc-shaped sides having equal radii of curva
ture, each of the legs having a slot extending through
its thickness and arranged equilaterally with the slots
in the other legs. Groups of four elements are assem
bled with a center element being engaged at each of
its slotted legs with a separate slotted leg of one of the
other elements. In one preferred embodiment a group
of twenty such elements are so assembled to form an
artistic sculpture.
4. Claims, 10 Drawing Figures
U.S. Patent Feb. 24, 1976 Sheet 1 of 4 3,940,100
U.S. Patent Feb. 24, 1976 Sheet 2 of 4 3,940,100
U.S. Patent Feb. 24, 1976 Sheet 3 of 4 3,940,100
U.S. Patent Feb. 24, 1976 Sheet 4 of 4 3,940,100
3,940, 100
1.
MODULAR CONSTRUCTION ELEMENT
BACKGROUND OF THE INVENTION
The present invention relates to a modular construc
tion element and, more particularly, to a flat construc
tion element for use in making furniture or artistic
sculptures.
Flat, modular elements have long been used in mak
ing children’s toys and such elements are often made of
thin, flexible materials which are deformable. Further
more, such elements sometimes have straight sides
which do not combine together to form a plurality of
curved lines and surfaces which give an artistic appear
ance and functional advantage.
The advantage of a modular construction for furni
ture is that the elements may be shipped flat in disas
sembled form to the end user, who can then simply fit
them together to create a piece of furniture. If the
elements are designed to be combined in a plurality of
different modes the end user has the option of creating
different artistic effects as well as different furniture
forms. One problem in all such modular furniture con
structions is in achieving a sturdy assembled structure
with elements which can be both easily assembled and
disassembled.
SUMMARY OF THE INVENTION
The above objectives are obtained and the problems
of prior art structures are overcome by the present
invention of a modular construction element compris
ing a flat member having three equilaterally arranged
legs and three equilaterally arranged, arc-shaped sides
having equal radii of curvature, each of the legs having
an open ended slot extending through its thickness,
oriented toward the centroid of the element, and ar
ranged equilaterally with the slots in the other legs.
These elements may be combined in groups of four
with at least one of the elements having the slot in each
of its legs interlocked with the slot in one leg of a sepa
rate one of the other three elements to form a sturdy
structure having one horizontal element and three ver
tical elements, for example.
In some preferred embodiments a plurality of such
four element groups are combined so that each of the
other three elements in each group has a slot in one of
its other legs interlocked with the slot in the other leg of
one of the other three elements of another group. The
maximum number of elements which can be assembled
symmetrically in such a combination is twenty. This
limit is a function of the inherent geometry of the ele
ment’s construction. Thereafter, the design merely
repeats itself.
Because of the arcuately shaped edges of each ele
ment the overall construction has certain advantages
that other modular constructions do not have. One
such advantage is that the basic construction of four
elements will securely seat a sphere-shaped object or
other rounded type objects. In the maximum symmetri
cal combination of twenty such elements they will de
fine a hollow, sphere-shaped space which may contain,
for example, a plastic sphere globe lamp, decorative
item, or other functional shapes such as a planter or
fireplace base.
The slots in each leg of each element serve a dual
purpose. In addition to providing an interlocking mech
anism for each of the modules, they also secure various
accessories to the base, such as beveled leg assemblies
10
15
20
25
30
35
40
45
50
55
60
65
2
which provide a stable base for an assembly of four or
more such units and which also can serve as table top
holders. Each element is made of a substantially rigid,
nonflexible material. In a preferred embodiment, the
material chosen is a plywood or other hard wood,
which is approximately one-fourth to one and one-half
inches thick.
In one preferred embodiment, the elements are
stackable for shipping by overlaying them one on top of
another and providing an interlocking member which is
wedged into the slots of the stacked elements to hold
them in place.
It is therefore an object of the present invention to
provide a modular construction element which is flat
and which may be assembled with three other such
elements to form a three-legged, stable base for sup
porting both sphere-shaped and plane-shaped objects.
It is another object of the invention to provide a
three-legged constructional element which may be
assembled in groups of four or more such elements
together to form an artistic work.
The foregoing and other objectives, features and
advantages of the invention will be more readily under
stood upon consideration of the following detailed
description of certain preferred embodiments of the
invention, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the basic, modular
construction element according to the invention;
FIG. 2 is a diagrammatic illustration of the geometric
construction of the element depicted in FIG. 1;
FIG. 3 is a perspective view of a group of four such
elements as depicted in FIG. 1 when joined together
according to the invention;
FIG. 4 is a perspective view of four of the elements
depicted in FIG. 1 when stacked together for shipping;
FIG. 5 is a perspective view illustrating a typical use
of a group of four such elements as depicted in FIG. 3
in combination with an artistic, sphere-shaped object;
FIG. 6 is a perspective view illustrating a typical use
of two groups of four such elements as depicted in FIG.
3 for supporting a table top;
FIG. 7 is a perspective view of a plurality of the ele
ments depicted in FIG. 1 when assembled into an artis
tic structure having an interior, sphere-shaped, hollow
space;
FIG. 8 is a side view, in elevation, and with portions
broken away, of the four element group depicted in
FIG. 3 together with a plane surface and a leg and
holder assembly;
FIG. 9 is an enlarged side view of the leg and holder
assembly depicted in FIG. 8; and
FIG. 10 is an enlarged plan view of the leg and holder
assembly depicted in FIG. 9.
DETAILED DESCRIPTION OF CERTAIN
PREFERRED EMBODIMENTS
Referring now more particularly to FIG. 1, a flat,
rigid element 10 according to the invention is depicted
which has three equilaterally spaced legs 12. Each leg
has a rectangularly shaped, open ended slot 14 through
its thickness and oriented axially toward the centroid of
the triangularly shaped element 10. Each of the three
slots 14 is also equilaterally arranged with respect to
the other slots. Thus, each of the legs 12 and each of
the slots 14 is oriented at 120° with respect to the other
3,940, 100
3
legs and slots, respectively. The sides 16 of each ele
ment 10 between each leg 12 are arc-shaped and have
the same radius of curvature.
The element 10 is made of a rigid material, such as
wood or plastic, and can be any thickness desired al
though in the preferred embodiment, the thickness
range is from one-fourth of an inch to one and one-half
inches. the width of the slot 14 should be only slightly
greater than the thickness of the element 10 so that
when an element leg 12 is inserted into the slot 14 it
will fit snugly. The axial length of the slots 14 is a mat
ter of design criteria, but it should be sufficient to pro
vide a rigid, interlocking mechanism when assembled
with the other elements as depicted in FIG. 3.
Referring now more particularly to FIG. 3, an assem
bly of four of the units 10 is depicted in which a center
element 10a is horizontal and is interlocked along each
of its slots 14 with corresponding slots 14 in each of
three other, vertical elements 10b, 10c and 10d. When
interlocked in this manner, the group of four elements
provides a sturdy, three-legged structure which will
support either a flat surface on the uppermost legs 12
of the elements 10b, 10c and 10d or a sphere-shaped
object in the uppermost curved sides 16 of each of the
upstanding elements 10b, 10c and 10d. The elements
10a, 10b, 10c and 10d are easily assembled into this
basic structure without the need to use glue or fasten
ing devices. The structure can also be easily disassem
bled for shipping or storage.
Referring now more particularly to FIG. 4, it can be
seen that each of the elements 10 depicted in FIG. 3
may be overlaid or stacked flat, one on top of another,
for ease in shipping or storage and the thus assembled
group may be held in this arrangement by placing
wedges (not shown) into the corresponding slots 14 of
the elements 10.
Referring now more particularly to FIG. 2, the geo
metrical construction of the element 10 is illustrated.
The element 10 is constructed within the perimeter of
a hypothetical, equilateral triangle 20. As described
above, each of the element sides 16 between the legs 12
is arc-shaped and has a radius of curvature 22, from a
corresponding, opposite vertice of the equilateral trian
gle 20, which is equal to the radius of curvature of each
10
15
20
25
30
35
40
of the other sides 16. The axial center line or axis of 45
symmetry of each leg 12 lies along individual, corre
sponding hypothetical lines 24 which intersect the mid
point of one of the sides of the triangle 20 and the
opposite vertex. While only one radius 22 and one
midline 24 are shown in FIG. 2 for purposes of clairty
in the illustration, it will be understood that other cor
responding radii and midlines 22 and 24, respectively,
can be similarly constructed for the other sides 16 and
the legs 12. It is this fundamental geometry of the ele
ment 10 which enables it to combine to form the shapes
depicted in FIGS. 1 and 3 and in the shape to be de
scribed in FIG. 7.
Referring now more particularly to FIGS. 5 and 6,
typical uses for the assembly of four elements depicted
in FIG. 3 are illustrated. In FIG. 5 a sphere-shaped,
artistic object 26 is supported along the upper curved
surfaces 16 of an assembly of four of the elements 10.
The sphere-shaped object 26 need not be a complete
sphere. It could also be bowl-shaped, such as for a
barbecue pit or a modern open-hearth stove. As illus
trated in FIG. 6, two or more of the four element
groups may be used to support a flat plane surface,
such as a table top 28.
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Referring now more particularly to FIG. 7, an artistic
sculpture made of a plurality of four element groups is
illustrated in which each of the elements 10b, 10c and
10d has a slot in one of its other legs interlocked with
the slot in the other leg of another one of the three
elements in another four-element group. The interior
curved sides 16 of the combined elements together
define a sphere-shaped, hollow space 30 which may be
left empty or which may be filled with a sphere-shaped,
artistic or ornamental object.
Referring now more particularly to FIGS. 8, 9 and
10, a combination leg and plane surface holder assem
bly 32 for use with a group of four elements is depicted
as comprising a pair of spaced apart, rigid, parallel
strips 34 which are joined together at one end by an
intermediate, rectangular cross-shape member 38. The
strips 34 and the member 38 are beveled at one end
and fitted with a non-skid surface 40, such as a rubber
pad, for example. The member 38 is thinner than the
width of the strips 34 and is nearly the same in thick
ness as the width of the notches 14 in the member legs
12.
The assembly 32 can thus be fitted into the notch 14
of a member leg 12 so that the member 38 is engaged
in the notch 14 and the spaced apart ends of the strips
34 which are distal from the member 38 overlap the flat
sides of the member 10 towards its center (see FIG. 8)
to hold the assembly 32 in rigid engagement with the
member 10. The angle of the bevel in the end is such
that the non-skid surface 40 is substantially horizontal
when the assembly 32 is engaged in the legs 12 of the
modular elements 10 fitted together in four element
groups. This feature provides a stable, horizontal foot
base for the four element groups and a stable, horizon
tal support for a table top, as shown in FIG. 8.
While certain uses have been depicted for the ele
ments of the invention, it should be apparent that nu
merous other combinations will be clear to those
skilled in the art upon reading the foregoing specifica
tion.
The terms and expressions which have been em
ployed here are used as terms of description and not of
limitations, and there is no intention, in the use of such
terms and expressions, of excluding equivalents of the
features shown and described, or portions thereof, it
being recognized that various modifications are possi
ble within the scope of the invention claimed.
What is claimed is:
1. In combination, a group of four inflexible, modular
construction elements, each element being flat and
having three equilaterally spaced legs with arc-shaped
sides between each leg, each of the arc-shaped sides
having the same radius of curvature, each of the legs
further having a slot through its thickness which ex
tends toward the centroid of the element, the width of
the slots being only slightly greater than the thickness
of the element, and at least one of the elements having
the slot in each of its legs fully inserted in the slot in one
leg of a separate one of the other three elements so that
one element is oriented perpendicularly to the other
three elements and is inflexibly interloced therewith to
form a rigid, load bearing structure whose constituent
elements are inflexible with respect to each other when
so interlocked.
2. A combination as recited in claim 1 further com
prising a plurality of such four element groups, each of
the other three elements in each group having a slot in
one of its other legs interlocked with the slot in the
3,940,100
S
other leg of one of the other three elements of another
group.
3. A combination as recited in claim 2 wherein there
are maximum of twenty interlocked elements.
4. A modular construction element comprising a flat
member having three equilaterally spaced legs with
arc-shaped sides between each leg, each of the arc
shaped sides having the same radius of curvature, each
of the legs further having a slot through its thickness
which extends toward the centroid of the element, the
width of the slot being only slightly greater than the
thickness of the element and further including a leg and
5
O
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50
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65
6
holder assembly having a pair of parallel strips and a
rectangularly shaped member mounted between and to
the strips at one end to space them apart, the strips and
the rectangular member being beveled at one end, the
strips being wider than the width of the leg slots, and
the rectangular member being thinner than the width of
the leg slots so that the leg and holder assembly can be
fitted to an element leg by engaging the rectangular
member in the leg slot with the strips overlying oppo
site sides of the element leg.
k ce k -k sk
United States Patent 19
USOO5819491A
11 Patent Number: 5,819,491
Davis (45) Date of Patent: *Oct. 13, 1998
54 MODULAR CONSTRUCTION ELEMENTS FOREIGN PATENT DOCUMENT
S
75 Inventor: Harry H. Davis, Mooresville, N.C. g S. R s E. R
73 Assignee: L.B. Plastics Limited, Derby, England 2 : ; ; ;2, in
4062646 9/1949 Japan ……………….. … 52/588.1
* Notice: The term of this patent shall not extend 0834.138 5/1960 United Kingdom ……………… 52/588.1
beyond the expiration date of Pat. No. 1004439 9/1965 United Kingdom.
5,647,184. 1080040 8/1967 United Kingdom.
OTHER PUBLICATIONS
21 Appl. No.:798,828
Heritage Marine, Classic Beauty Maintenance Free Dura
22 Filed: Feb. 12, 1997 bility, Submitted Pages, Published prior to Jan. 22, 1996,
Macon, MS.
Related U.S. Application Data Brock Manufacturing Maintenance-Free SavingS.
Enhanced Property Appearance., Submitted Pages, Pub
63 Continuation-in-part of Ser. No. 589,728, Jan. 22, 1996, Pat. lished prior to Jan. 22, 1996, Milford, IN.
No. 5,647,184. Mobil Chemical Company, Trex Wood-Polymer Compos
51) Int. Cl. …………………………… E04C 3700; E04B5/00 ite An Innovative Material From Mobil For Virtually
52 U.S. Cl. …………………….. 52/592.1; 52/588.1; 52/177; Maintenance-Free Decking And Landscaping., Submitted
52/6S0.3; 52/100; 52/731.3; 52/732.2 Pages, Published prior to Jan. 22, 1996, Norwalk, CT.
58 Field of Search ………………………….. 52/588.1, 589.1, Heritage Vinyl Products, Teck Deck-Vinyl . . . Is Final.,
52/591.1, 592.1, 100, 177,650.3, 730.5, Entire Brochure, Published prior to Jan. 22, 1996.
731.3, 732.2; 11.4/263, 266 Primary Examiner Robert Canfield
Attorney, Agent, or Firm Adams Law Firm, P.A.
56) References Cited
57 ABSTRACT
U.S. PATENT DOCUMENTS
An elongate modular decking plank is provided for assem
Re. 31,368 9/1983 Trumper. bly on a Supporting Subfloor together with a plurality of like
1913,342 6/1933 Schaffert. planks to form a decking Structure. The decking plank has a
3,043,407 7/1962 Marryatt. top wall spaced-apart from a bottom wall, and opposing
3,100,556 8/1963 De Ridder. laterallv Spaced downwardlv converging Side walls inter
3,432,147 3/1969 Schreyer et al. . y sp y ging
3. 440791 4/1969 Troutiner. connecting the top and bottom walls. An integrally-formed
3,555,762 1/1971 Costanzo, Jr. . flange extends outwardly from the bottom wall on one of
3,640,191 2/1972 Hendrich. Said Sides of the decking plank. The flange includes a
3,680,711 8/1972 Brucker. fastening portion for receiving fasteners therethrough to the
3,707,819 1/1973 Calhoun et al.. Supporting Subfloor to mount the decking plank on the
3.863,417 2/1975 Franchi. Supporting Subfloor, and a connecting portion for connecting
3,914,913 10/1975 Roberts. the plank to an adjacent like plank in a manner which
3,968,616 7/1976 Gostling. permits limited lateral and angular adjustment between
E. ty. SE et al. . adjacent planks. The plank is preferably extruded from
5,052,150 10/1991 Shvartsburd. high-impact polymeric material, Such as PVC plastic.
(List continued on next page.) 11 Claims, 9 Drawing Sheets
5,819,491
Page 2
5,088,910
5,159,788
5,204,149
U.S. PATENT DOCUMENTS
2/1992 Goforth et al. .
11/1992 Merrick.
4/1993 Phenicie et al. .
5,274.977
5,314,9
40
5,346,759
5,351,458
5,361,554
1/1994
5/1994
9/1994
10/1994
11/1994
Bayly .
Stone.
WII.
Lehe.
Bryan.
U.S. Patent Oct. 13, 1998 Sheet 1 of 9 5,819,491
U.S. Patent Oct. 13, 1998 Sheet 2 of 9 5,819,491
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5,819,491 Sheet 3 of 9 Oct. 13, 1998 U.S. Patent
U.S. Patent Oct. 13, 1998 Sheet 4 of 9 5,819,491
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U.S. Patent Oct. 13, 1998 Sheet 5 of 9 5,819,491
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U.S. Patent Oct. 13, 1998 Sheet 6 of 9 5,819,491
66
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57
5,819,491 Sheet 7 of 9 Oct. 13, 1998 U.S. Patent
ZEZCEZZA/
U.S. Patent Oct. 13, 1998 Sheet 8 of 9 5,819,491
U.S. Patent Oct. 13, 1998 Sheet 9 of 9 5,819,491
S
S
5,819,491
1
MODULAR CONSTRUCTION ELEMENTS
This application is a Continuation-in-Part of Ser. No.
08/589,728 filed Jan. 22, 1996, now U.S. Pat. No. 5,647,184.
TECHNICAL FIELD AND BACKGROUND OF
THE INVENTION
This invention relates to modular construction elements in
the nature of planks and to Structures formed from an
assembly of Such planks. The invention is applicable, for
example, in the construction of boat docks, piers, decks,
patios, walkways, pontoon boat floors, and the like.
According to one prior art plastic decking plank, Separate
cap and base elements are Snapped together to form a single
plank. The base element is first mounted directly to the
Subfloor with fastenerS Such as Screws or nails. Mating
components of the cap and base elements are then manually
aligned, and a rubber hammer or other tool is used to
Snap-attach the pieces together. Unlike the invention, Such
two-piece designs generally require Substantial time and
effort to assemble. The present one-piece design results in a
considerably Stronger and more rigid decking Structure than
a two-piece design while minimizing manufacturing and
installation costs. In addition, due to the absence of engaging
parts, the invention also produces less Surface noise or
Squeaking than two-piece designs.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a modular,
one-piece plastic construction element which may be readily
assembled together with a number of like elements to form
a decking or other Structure.
It is another object of the invention to provide a modular
decking plank which includes complementary, integrally
formed male and female fastener components.
It is another object of the invention to provide a modular
decking plank which is relatively inexpensive to manufac
ture.
It is another object of the invention to provide a decking
plank which includes hidden fasteners located below the top
Surface of the decking Structure for mounting the plank to a
Supporting Subfloor.
According to the invention there is provided an elongate
modular construction element for assembly with a plurality
of like elements to form a structure Such as decking, said
element being in the nature of a plank comprising Spaced top
and bottom walls interconnected by opposed side walls to
define a void therein, first connecting means projecting
outwardly beyond one of first and Second Sides of the plank,
Second connecting means complementary to Said first con
necting means being formed at the opposite Side of the plank
whereby two Such planks may be connected together in Side
by Side relation, Said connecting means being adapted to
permit limited sliding movement of adjacent planks relative
to one another in a direction transverse to the lengths of the
planks and limited angular movement about an axis extend
ing parallel to the lengths thereof, whereby to permit the top
walls of adjacent planks to be angularly inclined relative to
one another to accommodate irregularities in a base or other
Supporting Structure on or by which the resultant decking or
other Structure is Supported.
Preferably Said connecting means are located adjacent the
bottom wall of and extend continuously along the plank
from one end thereof to the other. Preferably also said first
connecting means comprises a laterally projecting flange
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2
including a fastening portion for receiving fasteners there
through for attaching the plank to Said Supporting Structure.
Preferably said Second connecting means comprises a
channel extending adjacent Said bottom wall at the opposite
Side of the decking plank from Said first connecting means
for receiving a connecting portion of Said flange.
The invention also provides a decking or other structure
formed from a plurality of interconnected modular construc
tion elements as aforesaid.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described,
by way of example only, with reference to the accompanying
drawings, in which:
FIG. 1 is a fragmentary perspective view of a decking
Structure comprising an assembly of decking planks accord
ing to one embodiment of the invention;
FIG. 2 is a fragmentary perspective view of a number of
decking planks mounted on joists of a Supporting Subfloor,
showing the connecting means for locking adjacent planks
together;
FIG. 3 is an end view of one of the decking planks shown
in FIG. 2;
FIG. 4 is an enlarged view of the circled area A in FIG.
3 showing a portion of the Slip-resistant top Surface of the
decking plank,
FIG. 5 is an enlarged view of the circled area B in FIG.
3 showing an integrally-formed flange of the decking plank;
FIG. 6 is an enlarged view of the circled area C in FIG.
3 showing an integrally-formed complementary channel of
the decking plank,
FIG. 7 is an enlarged view of the circled area D in FIG.
3 showing an integrally-formed trim channel of the decking
plank;
FIG. 8 is an end view of an elongate fastener strip used for
initiating decking construction;
FIG. 9 is an end View of an elongate decking trim Section
for attachment to a longitudinal Side of the decking plank;
FIG. 10 is an end view of an elongate cap member for
attachment to exposed ends of the decking planks,
FIG. 11 is a perspective view of an alternative end cap for
attachment to a distal end of a Single decking plank;
FIG. 12 is an end view of an elongate T-section for
positioning adjacent to abutting ends of the decking planks,
FIG. 13 is a croSS-Sectional view of two adjacent decking
planks attached together;
FIG. 14 is an enlarged fragmentary perspective view
showing a decking trim according to FIG. 9 positioned for
attachment to a decking plank adjacent an exposed side edge
of the decking Structure;
FIG. 15 is an enlarged fragmentary perspective view
showing a flange according to FIG. 8 used for beginning
decking construction, and a cap member according to FIG.
10 positioned for attachment to a decking plank, and
FIG. 16 is an enlarged fragmentary view showing a
modified form of connecting means.
DESCRIPTION OF THE PREFERRED
EMBODIMENT AND BEST MODE
Referring to the drawings, a decking Structure according
to the present invention is illustrated in FIG. 1 and shown
generally at 10. The decking structure 10 is constructed of an
assembly of one-piece modular construction elements in the
5,819,491
3
form of decking planks 20 mounted on Supporting joists 11
of a subfloor using wood screws 12, as shown in FIG. 2, or
other suitable fasteners (not shown). The decking planks 20
are formed of an extruded high impact, UV stabilized
polymeric material, Such as PVC plastic, and are easily cut
with a hand Saw or electric circular saw to any desired
length. According to the embodiment disclosed, the width of
the decking plank 20 is 5.750 inches, and the height is 1.625
inches. The maximum space between adjacent planks is
approximately 0.25 inches. Numerous other dimensions are
possible within the scope of the invention. Moreover, while
a boat dock is illustrated in FIG. 1, the invention has further
application in construction of patio decks, piers, walkways,
balconies, and the like.
Referring to FIGS. 2 and 3, the decking plank 20 includes
integrally-formed top and bottom walls 21 and 22, and
opposing Side walls 23 and 24. Integral reinforcing ribs 25,
26, 27, 28, and 29 are located between the side walls 23 and
24, and bridge the top and bottom walls 21 and 22. The ribs
25-29 extend longitudinally from one end of the decking
plank 20 to the opposite end for increasing its load-resisting
capacity. The Side walls 23 and 24 converge towards the
bottom wall 22 at an angle of about 20.
A portion of the top wall 21 is illustrated in detail in FIG.
4. The top Surface includes a number of alternately-spaced
Serrations 31 and risers 32 extending along the entire length
of the decking plank 20, and laterally from one side edge of
decking plank 20 to the other. In the illustrated embodiment,
the serrations 31 extend 0.015 inches above the top surface
of the decking plank 20, and are Spaced approximately 0.030
inches apart from each other. The risers 32 extend 0.062
inches above the top Surface, and are spaced approximately
0.25 inches apart. The rough texture provided by the Serra
tions 31 and risers 32 creates a relatively slip-resistant
decking Surface.
As shown in FIGS. 2, 3, and 5, an integrally-formed
flange 35 extends outwardly from and along the bottom wall
22 on one Side of the decking plank 20 along its entire
length. The flange 35 includes a fastening portion 35A
having a number of Spaced openings 37 for receiving the
Wood Screws 12 therethrough to the Supporting joists 11, and
for water drainage from a top Surface of the decking Struc
ture 10. According to a preferred embodiment, the openings
37 are Spaced 4.0 inches apart along the length of the flange
35 so that the planks 20 can be mounted to standard 16 inch
centre joists. The unused openings 37 between the joists 12
are thus available for drainage.
In a modification the preformed openings 37 may be
omitted, a Small longitudinally extending groove 38 being
formed in the flange 35 to help guide the screws 12 through
the flange 35 and into the joists 11 of the subfloor. Enhanced
water drainage may be achieved by Sloping the decking
plank 20 slightly from one end to the other. This embodi
ment of the invention without openings 37 is especially
applicable for use in overhead decking whereby an area
below the decking is sheltered from rain water runoff.
A connecting portion 35B of the flange 35 is integrally
formed with the fastening portion 35A, and provided for
attaching the decking plank 20 to an adjacent like plank. The
connecting portion 35B extends outwardly in a plane above
the fastening portion 35A and engages with a fastening
channel 41 of the adjacent plank 20, as is best shown in FIG.
13.
The channel 41 is integrally formed along the bottom wall
22 on the side of the decking plank 20 opposite the flange 35.
The channel 41 extends longitudinally along the entire
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length of the decking plank 20, and cooperates with the
connecting portion 35B of the flange 35 to space the adjacent
planks 20 from each other and to attach the adjacent planks
20 together. The connecting portion 35B and channel 41
include interfering shoulders 43 and 44 providing a Snap
attachment to lock the adjacent decking planks 20 to each
other while permitting a limited degree of relative lateral
movement between them.
The top walls of the adjacent planks may thus abut one
another or be spaced apart to a limited variable extent.
Spacing of the top walls creates Series of longitudinal Slots
in the upper Surface of the decking Structure, through which
Surface water may drain into the generally triangular
recesses defined by the sloping side walls 23 and 24 of the
adjacent planks and the connecting members 3 5. These
recesses may also serve to accommodate electrical or other
cables to Supply Services at Spaced locations along the
assembled structure. Moreover by virtue of the relatively
loose engagement between the connecting members 35 and
41, a limited degree of angular movement is permitted
between adjacent planks to accommodate irregularities in
level of the Supporting joists 11.
A second channel or recess 49 is formed in the side wall
23 adjacent to the bottom wall 22 for receiving a flange
portion 51A of decking trim 51 shown in FIGS. 1,9, and 14.
The decking trim 51 is used to finish an exposed side edge
of the decking structure 10, as described further below.
To construct the decking, an elongate fastener Strip 45,
shown in FIGS. 1, 8, and 15, is first mounted on the
Supporting joists 11 at a side edge “E1’ of the decking
Structure. A longitudinally extending groove 46 is formed in
a mounting portion 45A of the strip 45 for guiding wood
screws 12 or other fasteners therethrough to the joists 11. A
first decking plank 20 is placed on the joists 11, and its
fastening channel 41 Snap-attached to a locking portion 45B
of the fastener strip 45. A locking shoulder 47 is formed with
the portion 45B, and cooperates with the shoulder 44 of the
channel 41 to lock the decking plank 20 and fastener strip 45
together while permitting a limited degree of relative lateral
movement between them. Successive planks 20 are then
Snap-attached together by inserting the connecting portion of
the flange 35 of one plank 20 into the channel 41 of an
adjacent plank, as shown in FIG. 13. The planks 20 are
Secured one-by-one to the joists 11 by Screws 12 as
described above. The complementary connecting portions
35B and channels 41 of respective, adjacent planks 20
cooperate to Space the plankS 20 a predetermined distance
from each other within the range of lateral adjustment
permitted by the construction of these components. Separate
Spacers (not shown) may be used to achieve exact parallel
spacing between adjacent planks.
Referring to FIGS. 1, 3, and 9, upon reaching a second
Side edge “E2 of the proposed decking Structure, the flange
35 of the last fitted decking plank 20 is removed using a saw
at a groove 48 formed at the junction of the bottom wall 22
and the flange 35. The groove 48 preferably extends along
the entire length of the decking plank 20 and forms a parting
line, as described above. After removing the flange 35, a
locking portion 51A of a decking trim 51 is inserted into the
trim channel 49 at the side edge “E2” of the decking
structure 10. As best shown in FIG. 14, the portion 51A and
the channel 49 include interfering shoulders 52 and 53 for
providing a convenient Snap-attachment to lock the trim 51
and decking plank 20 together. A groove 54 is formed in the
web 51B of the decking trim 51 for receiving screws 12 to
Secure the trim 51 directly to the adjacent Supporting joist
11. If desired the joists 11 may be covered with an elongate
plastic or vinyl cladding (not shown).
5,819,491
S
Referring to FIGS. 1, 10, and 15, at an adjacent side edge
“E3′ of the decking structure 10, an elongate C-shaped cap
55 shown in FIGS. 10 and 15 may be applied to the exposed
ends of the decking plankS 20 to provide a more attractive
and aesthetic Side finish. The cap 55 includes Spaced apart
resilient arms 56 and 57 which slightly converge so that
when they are spread and forced onto the exposed ends of
plankS 20, they frictionally engage the planks 20. One or
more caps 55 may be used to finish the exposed side edge
“E3”. Alternatively, each plank 20 can be fitted with an end
cover 61 Such as shown in FIG. 11.
In addition, as shown in FIGS. 1 and 12, an elongate cover
trim 62 of T-Section may be positioned at mitered, abutting
ends of decking plankS 20 to provide a uniform and aesthetic
transition between the planks 20. The T-section trim 62
includes a textured top Surface with alternately spaced
serrations 63 and risers 64, and a centre web 63 for locating
between the abutting planks 20. The T-section trim 62 and
end cap 55 may be further secured to the decking planks 20
with an adhesive or other Suitable fastener if desired.
FIG. 16 shows a modified form of connecting means
similar to that shown in FIG. 13 but in which the shoulders
143 and 144 have opposing sloping faces 143A, 143B and
144A, 144B. The sloping faces 143B and 144B replace the
vertical abutting faces of the shoulders of FIG. 13 and
facilitate disengagement of the connecting means and Sepa
ration of adjacent planks if required. The cooperating shoul
ders on the trim components of FIGS. 8 and 9 and the
shoulder 53 may also be modified in a similar manner.
The decking Structure described has numerous advantages
over previously proposed wooden or plastic decking Struc
tures. There are no exposed nails or other fasteners at the
Surface of the decking Structure which require replacement,
or could cause injury. The embossed top Surface provides
enhanced slip-resistance and the integral construction of the
individual planks avoids the need to engage interfitting
components to form each plank. The manner of intercon
nection of the planks permits limited lateral adjustment
between adjacent planks to accommodate to different overall
widths of Substructure and provides multiple drainage slots
to clear water rapidly from the assembled Structure.
It should be appreciated that while the invention is
primarily intended for use in the construction of marine
walkways and decking, plank elements according to the
invention may also be used to construct cladding, Screen
fencing or other forms of Structure.
I claim:
1. An elongate modular construction element for assem
bly with a plurality of like elements to form a decking
Structure, Said element being in the nature of a hollow plank
comprising Spaced top and bottom walls interconnected by
opposed side walls, first connecting means projecting out
Wardly beyond one of Said Side walls of the plank, Second
connecting means complementary to Said first connecting
means being formed at the opposite Side of the plank
whereby two Such planks may be connected together in Side
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by Side relation, the Side walls of each plank converging in
a direction towards Said bottom wall So as to be adapted to
define between adjacent interconnected planks a Void of
increasing width from the top to the bottom thereof, Said
connecting means being adapted to permit limited sliding
movement of adjacent plankS relative to one another in a
direction transverse to the lengths of the planks and limited
angular movement about an axis extending parallel to the
lengths thereof whereby the top walls of adjacent planks
may be angularly inclined relative to one another, Said
connecting means being located adjacent the bottom wall of
and extending continuously along the plank from one end
thereof to the other, and Serving, when adjacent planks are
connected together, to close off the bottom of Said Void.
2. A construction element according to claim 1, wherein
Said first connecting means comprises a laterally projecting
flange including a fastening portion for receiving fasteners
therethrough for attaching the plank to Said Supporting
Structure.
3. A construction element according to claim 2, wherein
Said flange includes a connecting portion extending in a
plane parallel to but offset from the plane of Said fastening
portion.
4. A construction element according to claim 3, wherein
Said Second connecting means comprises a channel extend
ing adjacent Said bottom wall at the opposite side of the
plank from Said first connecting means for receiving the
connecting portion of Said flange.
5. A construction element according to claim 4, including
locking means comprising cooperating interfering shoulders
formed respectively on the connecting portion of Said flange
and within Said channel.
6. A construction element according to claim 2 including
a longitudinally-extending groove formed in the fastening
portion of Said flange for guiding Said fasteners therethrough
to Secure the plank to a Supporting Structure.
7. A construction element according to claim 2 including
a plurality of Spaced-apart holes formed in Said fastening
portion of Said flange for accommodating passage of fas
teners therethrough to a Supporting Structure.
8. A construction element according to claim 7 including
a groove formed along the length of the fastening portion of
Said flange to enable removal of the flange from a plank
positioned at an exposed edge of an assembled Structure.
9. A construction element according to claim 1 including
a further channel formed adjacent Said first connecting
means for receiving a trim member adapted to cloak the
exposed edge of an assembled Structure.
10. A construction element according to claim 1 including
a plurality of reinforcing ribs located between Said Side walls
and interconnecting Said top and bottom walls.
11. A structure comprising a plurality of interconnected
modular construction elements according to claim 1
assembled together on a Supporting Structure.
Case Study
Application of Modular Construction
in High-Rise Buildings
R. Mark Lawson, M.ASCE1; Ray G. Ogden2; and Rory Bergin3
Abstract: Modular construction is widely used in Europe for multi-story residential buildings. A review of modular technologies is
presented, which shows how the basic cellular approach in modular construction may be applied to a wide range of building forms
and heights. Case studies on 12-, 17-, and 25-story modular buildings give design and constructional information for these relatively tall
buildings. The case studies also show how the structural action of modular systems affects the architectural design concept of the building.
The combination of modules with steel or concrete frames increases the range of design opportunities, particularly for mixed-use commercial
and residential buildings. An overview of the sustainability benefits and economics of modular construction is presented based on these
case studies. DOI: 10.1061/(ASCE)AE.1943-5568.0000057. © 2012 American Society of Civil Engineers.
CE Database subject headings: High-rise buildings; Residential buildings; Construction; Economic factors; Europe; Methodology.
Author keywords: Modular; Steel; Residential; High-rise; Construction; Economics.
Introduction
Modular construction comprises prefabricated room-sized volu-
metric units that are normally fully fitted out in manufacture
and are installed on-site as load-bearing “building blocks.” Their
primary advantages are:
• Economy of scale in manufacturing of multiple repeated units,
• Speed of installation on-site, and
• Improved quality and accuracy in manufacture.
Potentially, modular buildings can also be dismantled and re-
used, thereby effectively maintaining their asset value. The current
range of applications of modular construction is in cellular-type
buildings such as hotels, student residences, military accommoda-
tions, and social housing, where the module size is compatible with
manufacturing and transportation requirements. The current appli-
cation of modular construction of all types is reviewed in a recent
Steel Construction Institute publication (Lawson 2007). Lawson
et al. (2005) describe the mixed use of modules, panels, and steel
frames to create more adaptable building forms.
There are two generic forms of modular construction in steel,
which affects their range of application and the building forms that
can be designed:
• Load-bearing modules, in which loads are transferred through
the side walls of the modules.
• Corner-supported modules, in which loads are transferred via
edge beams to corner posts (see Fig. 1).
In the first case, the compression resistance of the walls (gen-
erally comprising light steel C-sections at 300 to 600 mm spacing)
is the controlling factor. The double layer walls and floor/ceiling
combination enhances the acoustic insulation and fire resistance
of the construction system.
In the second case, the compression resistance of the corner
posts is the controlling factor and for this reason, square hollow
sections (SHS) are often used due to their high buckling resistance.
Resistance to horizontal forces, such as wind loads and robust-
ness to accidental actions, become increasingly important with the
scale of the building. The strategies employed to ensure adequate
stability of modular assemblies, as a function of the building
height, are:
• Diaphragm action of boards or bracing within the walls of the
modules–suitable for 4- to 6-story buildings.
• Separate braced structure using hot-rolled steel members lo-
cated in the lifts and stair area or in the end gables—suitable
for 6- to 10-stories.
• Reinforced concrete or steel core–suitable for taller buildings.
Modules are tied at their corners so that structurally they act
together to transfer wind loads and to provide for alternative load
paths in the event of one module being severely damaged. For taller
buildings, questions of compression resistance and overall stability
require a deeper understanding of the behavior of the light steel
C-sections in load-bearing walls and of the robust performance
of the interconnection between the modules.
Modular Construction in High-Rise Residential
Buildings
Spatial Arrangement of the Modules
Designing with modular construction is not a barrier to creativity.
Modular rooms or pairs of rooms or room and corridor modules can
be used to create varieties of apartment types. These types can be
put together to make interesting and varied buildings of many
forms. The nature of high-rise buildings is such that the modules
are clustered around a core or stabilizing system. The particular
features of the chosen modular system have to be well understood
by the design team at an early stage so that the detailed design con-
forms to the limits of the particular system.
1SCI Professor of Construction Systems, Univ. of Surrey, Faculty
of Engineering and Physical Sciences, Guildford, UK, GU2 7XH (corre-
sponding author). E-mail: m.lawson@surrey.ac.uk
2Professor of Architectural Technology, Oxford Brookes Univ., Oxford,
UK.
3Head of Sustainability, HTA Architects, London, UK.
Note. This manuscript was submitted on December 7, 2010; approved
on July 19, 2011; published online on July 21, 2011. Discussion period
open until November 1, 2012; separate discussions must be submitted
for individual papers. This paper is part of the Journal of Architectural
Engineering, Vol. 18, No. 2, June 1, 2012. ©ASCE, ISSN 1076-0431/
2012/2-148–154/$25.00.
148 / JOURNAL OF ARCHITECTURAL ENGINEERING © ASCE / JUNE 2012
J. Archit. Eng. 2012.18:148-154.
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http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
A typical module is 3.3 m (11 ft) to 3.6 m (14 ft) wide (internal
dimensions) and 6 m (20 ft) to 9 m (30 ft) long. A module is 25 to
35 m2 (270 to 375 ft2) in floor area and is often used for single-
person accommodation. Two modules are generally suitable for a
2-person apartment (with one bedroom) and three or four modules
are suitable for family-sized apartments (Lifetime Homes 2010).
In all cases, the kitchens and bathrooms are arranged next to the
corridor or other accessible space so that service connections and
maintenance can be carried out relatively easily.
For modules with load-bearing walls, the side walls of the mod-
ules should align vertically through the building, although openings
of up to 2.5 m width can be created, depending on the loading. For
modules with corner posts, the walls are non-load-bearing, but the
corner posts must align and be connected throughout the building
height. Additional intermediate posts may be required in long mod-
ules, so that the edge beams are not excessively deep.
The design of high-rise modular buildings is strongly influenced
by structural, fire, and services requirements. From a building
layout viewpoint, two generic floor plans may be considered for
the spatial relationship of the modules around a stablizing concrete
core:
• A cluster of modules, which are accessed from the core or from
lobbies next to the core, as illustrated in Fig. 2.
• A corridor arrangement of modules, in which the modules are
accessed from corridors either side of the core, as illustrated
in Fig. 3.
The addition of external balcony systems can be used to create a
layer of external features that provide private space and architec-
tural interest. Balconies can be attached at the corner posts of the
modules or can be ground supported. Integral balconies within
the modules may be provided by bringing the end wall in-board
of the module.
The optimum use of modular construction can achieved by
designing the highly serviced and hence more expensive parts
of the building in modular form and the more open-plan space
as part of a regular structural frame in steel or concrete. This re-
quires careful consideration of the architecture and spatial planning
of the building.
Structural Action of Tall Modular Buildings
The structural behavior of an assembly of modules is complex be-
cause of the influence of the tolerances in the installation pro-
cedure, the multiple inter connections between the modules, and
the way in which forces are transferred to the stabilizing elements,
such as vertical bracing or core walls. The key factors to be taken
into account in the design of high-rise modular buildings are:
• The influence of installation eccentricities and manufacturing
tolerances on the additional forces and moments in the walls
of the modules (Lawson and Richards 2010).
• Second-order effects due to sway stability of the group of mod-
ules, especially in the design of the corner columns of the
modules.
• Mechanism of force transfer of horizontal loads to the stabiliz-
ing system, which is generally a concrete core.
• Robustness to accidental actions (also known as structural
integrity) for modular systems.
In modular systems with load-bearing walls, axial load is trans-
ferred via direct wall-to-wall bearing, taking into account eccen-
tricities in manufacture and installation of the modules, which
causes additional buildup of moments and accentuates the local
bearing stresses at the base of the wall.
Two layers of plasterboard or similar boards are attached to
the internal face of the wall by screws at not more than
Fig. 1. Light steel module with a perimeter framework (image by
R. M. Lawson)
Fig. 2. Typical layout of rooms clustered around a core
Fig. 3. Typical corridor arrangement of modules
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300 mm spacing. Cement particle board (CPB) or oriented strand
board (OSB) are often attached to the exterior of the walls of the
modules. In production, boards may be fixed by air-driven pins
enhanced by glued joints. These boards restrain the C-sections
against buckling in the in-plane direction of the wall.
The ability of an assembly of modules to resist applied loads in
the event of serious damage to a module at a lower level is depen-
dent on the development of tie forces at the corners of the modules.
The loading at this so-called accidental limit state is generally taken
as the self-weight plus one-third of the imposed load, reflecting the
average loading on all floors in this rare event. To satisfy “robust-
ness” in the event of accidental damage to one of the modules,
the tie forces between the adjacent modules may be established
on the basis of a simplified model in which the module is
suspended from its neighbors. For design purposes, it is recom-
mended (Lawson et al. 2008) that the minimum horizontal force
in any tie between the modules is taken as not less than 30% of
the total load acting on the module and not less than 30 kN (3 tons).
Fire Resistance and Acoustic Insulation
In most European countries, 120-min fire resistance is required for
residential buildings of more than 28 stories in height (10 stories
typically), and in some countries sprinklers are also required. The
fire resistance of modular construction derives from four important
aspects of performance:
• The stability of the light steel walls is a function of the load
applied to the wall and the fire protection of the internal face
of the wall of the module.
• The load capacity of the module floor is influenced by the
thermal-shielding effect of the ceiling of the module beneath.
• The elimination of fire spread by fire barriers placed between
the modules (to prevent the spread of smoke or fire in the cavity
between the modules).
• The limiting of heat transfer through the double-leaf wall and
floor-ceiling construction of the modules.
Generally, the internal face of the walls and ceiling of the mod-
ule are provided with two 15 mm (0.6 in.) plasterboard layers
(at least one layer being fire-resistant plasterboard using vermicu-
lite and glass fiber). Mineral wool is placed between the C-sections
(also required for acoustic purposes). The floor and ceiling in com-
bination and the load-bearing light steel walls generally achieve
120-min fire resistance, depending on the sheathing board used
on the outside of the modules.
The double-layer walls and floor-ceiling of the modules also
provides excellent resistance to airborne and impact sound, particu-
larly when supplemented by external sheathing board. Additional
sound reduction and floor stiffness to minimize vibrations can be
achieved by a thin concrete floor screed either placed on the light
steel floor or as a composite slab spanning between the walls or
edge beams.
Case Study of Modules Stabilized by a Concrete
Core—Paragon, West London
For high-rise buildings, the modules are generally designed to resist
only vertical loads, including the cladding and corridor loads, and
horizontal loads are transferred to the concrete core. In the cluster
arrangement, the modules are connected directly to the core, gen-
erally by attaching ties to cast-in plates in the core. In the corridor
arrangement, horizontal loads are transferred via in-plane bracing
in the corridors and are again connected to the core. It follows that
the distance of the outer module from the core is limited by the
shear force that can be transferred via the corridor or by the travel
distance for fire evacuation purposes.
This concept has been used on one major project called Paragon
in west London, shown in Fig. 4 (Cartz and Crosby 2007). A series
of buildings from 11 to 17 stories were constructed using modules
with loadbearing corner posts. The plan form of the L-shaped
building is shown in Fig. 5. The modules were also manufactured
with integral corridors, in which half of the corridor was included in
each module. The corner columns were therefore in-board of the
ends of the modules and the projection of the floor into the corridor
was achieved by the stiff edge beams of the modules.
The project consisted of a total of 827 modules in the form of
600 en-suite student rooms, 114 en-suite studio rooms, and 44 one-
bedroom and 63 two-bedroom key worker apartments. The
17-story building consists of 413 modules. Modules are 2.8 m
(9 ft) to 4.2 m (13.5 ft) wide, which is the maximum for motorway
transport in the UK. The edge beams use 200 × 90 (8 × 3:5 in)
parallel flange channels (PFC) at floor level and 140 × 70
(5:5 × 2:7 in) PFC at ceiling level to design partially open-sided
modules of up to 6 m (20 ft) span. The one- or two-bedroom apart-
ments were constructed using two or three modules, each with a
35 to 55 m2 (375 to 590 ft2) floor area. The plan form is presented
in Fig. 6, which shows the many variations in room layouts that
were possible using corner-supported modules.
Case Study of Modules on a Podium—Bond Street,
Bristol
Modular construction may be combined with steel or concrete
frames to extend the flexibility in space planning in applications
where the dimensional constraints of modular systems would
otherwise be too restrictive. An adaptation of modular technology
is to design a “podium” or platform structure on which the modules
are placed. In this way, open space can be provided for retail or
commercial use or below-ground car parking. Support beams
should align with the walls of the modules and columns are typi-
cally arranged on a 6 to 8 m grid (20 to 26 ft). A column grid of
Fig. 4. 17-story modular building stabilized by a concrete core (image
by R. M. Lawson)
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7.2 m (24 ft) is optimum for car parking at ground floor or
basement.
Fig. 6 shows a 12-story mixed student residence and commer-
cial building in Bristol in the west of England, in which 6 to 10
stories of modules sit on a 2-story steel framed podium. The
400 bedroom modules are 2.7 m (9 ft) external width, but approx-
imately 100 modules are combined in pairs to form “premium”
studios consisting of two rooms. The kitchen modules are 3.6 m
(12 ft) external width. Stability is provided by four braced steel
cores, into which some modules are placed. The plan form is illus-
trated in Fig. 7. A double corridor is provided so that a cluster of
five rooms forms one compartment. Stability is provided by braced
steel cores and the maximum number of modules placed between
the cores is seven.
The building used a lightweight cladding system consisting of a
“rain screen” in which the self-weight of the cladding is supported
by the modules. The air and weather-tight layers and the majority of
insulation is contained within the module as delivered.
Case Study of High-rise Building in Wolverhampton
A 25-story modular construction project in Wolverhampton in the
midlands of England was studied to obtain data on the construction
process. It has three blocks of 8 to 25 stories and in total consists of
824 modules. The tallest building is Block A, which is shown in
Fig. 8 during construction. The total floor area in these three build-
ings is 20;730 m2 (223;000 ft2), including a podium level. The
floor area of the modules represents 79% of the total floor area.
The average module size was 21 m2 (226 ft2) but the maximum
size was as large as 37 m2 (398 ft2).
The project started on site in July 2008 and was handed over to
the client in August 2009 (a total of 59 weeks). Installation of the
modules started in October 2008 after completion of the podium
slab, and construction of the concrete core to Block A was carried
out in parallel with the module installation on Blocks C and B.
Importantly, the use of offsite technologies meant that the site acti-
vities and storage of materials were much less than in traditional
Fig. 5. Plan form of the building in Fig. 4 showing the location of the corner posts in the modules
Fig. 6. 12-story modular student residence at Bond Street, Bristol
(image by R. M. Lawson)
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construction, which was crucial to the planning of this project.
The tallest building, Block A, has various set-back levels using can-
tilevered modules to reduce its apparent size. Lightweight cladding
was used on all buildings and comprises a mixture of insulated
render and composite panels, which are attached directly to the
external face of the modules. The total area of cladding was
10;440 m2 (112;300 ft2) for the 3 blocks.
Construction Data
The module weights varied from 10,000 to 25,000 kg, depending
on their size, and the module self-weight was approximately
5:7 kN∕m2 (120 pounds∕ft2) floor area. The modules in the first
Block C were installed by mobile crane, whereas the modules
in Blocks A and C were installed by the tower crane that was
supported by the concrete core. The installation period for the
824 modules was 32 weeks and the installation team consisted
of a total of eight people plus two site managers. The average
installation rate was 7 modules per day, although the maximum
achieved was as high as 15 per day. This corresponds to
14.5 man-hours per module.
The overall construction team for the nonmodular components
varied from a further 40 to 110 with three to four site managers,
increasing as the 59-week project progressed. It was estimated that
the reduction in construction period relative to site-intensive
concrete construction was over 50 weeks (or a saving of 45% in
construction period).
It was estimated that the manufacture and in-house management
effort was equivalent to a productivity of 7.5 man-hours per square
meter module floor area (0.7 man-hours per square foot) for a
21 m2 (225 ft2) module floor size. This does not take into account
the design input of the architect and external consultants, which
would probably add about 20% to this total effort.
For modules at the higher levels, approximately 14% of the
module weight was in the steel components and 56% in the con-
crete floor slab. At the lower levels of the highrise block, the steel
weight increased to 19% of the module weight. The steel usage
varied from 67 to 116 kg∕m2 (14 to 24 pounds∕ft2) floor area,
which is higher than the 50 to 60 kg∕m2 (10 to 12 pounds∕ft2)
for medium-rise modular systems.
The estimated breakdown of man-effort with respect to the com-
pleted building was 36% in manufacture, 9% in transport and
installation, and 55% in construction of the rest of the building.
The total effort in manufacturing and constructing the building
was approximately 16 man-hours per square meter (1.5 man−hours
per square foot) completed floor area, which represents an esti-
mated productivity increase of about 80% relative to site-intensive
construction.
Deliveries and Waste
Site deliveries were monitored over the construction period. During
installation of the modules, approximately six major deliveries per
day were made, plus the six to twelve modules delivered on aver-
age. During concreting of the cores, approximately 6 × 8 m3
(280 ft3) concrete wagons were scheduled to be pumped to con-
struct the core at a rate of one story every three days.
Waste was removed from site at a rate of only two skips of
6 m3 (210 ft3) volume per week during the module installation
period and six skips per week in the later stages of construction,
equivalent to approximately, 3,000 kg of general waste, including
off-cuts and packaging. This is equivalent to about 9 kg per m2
(1:8 pounds per ft2) floor area.
Fig. 7. Plan of modular building at Bond Street, Bristol, showing the irregular-shaped core positions
Fig. 8. 25-story modular building in Wolverhampton, England, during
construction (image by R. M. Lawson)
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The manufacturing waste was equivalent to 25 kg∕m2
(5:1 pounds∕ft2) of the module area, of which 43% of this waste
was recycled. For the proportion of module floor area to total area
of 79%, this is equivalent to about 5% of the weight of the overall
construction. This may be compared to an industry average of
10 to 13% wastage of materials, with little waste being recycled.
It follows that modular construction reduces landfill by a factor of
at least 70%.
Summary of Sustainability Benefits of Modular
Construction
Modular construction systems provide several opportunities to
improve the sustainability of the project in terms of the construction
process and the performance of the completed building.
• Construction waste is substantially reduced from 10 to 15%
in a traditional building site to less than 5% in a factory envi-
ronment, which also has greater opportunities for recycling
of waste.
• The number of visits to site by delivery vehicles is reduced by
up to 70%. The bulk of the transport activity is moved to the
factory, where each visit can be used to deliver more material
than is usually delivered to a construction site.
• Noise and disruption are reduced on-site, assisted by the 30 to
50% reduction in the construction period, which means that
neighboring buildings are not affected as much as in traditional
building processes.
• The air-tightness and the thermal performance of the building
fabric can be much higher than is usually achieved on-site
due to the tighter tolerances of joints that can be achieved in
a factory environment.
• The efficient use of lightweight materials and the reduced waste
means that the embodied energy of the construction materials is
also reduced.
• Acoustic insulation is greatly improved by the double-layer
construction.
• Safety on-site and in the factory is greatly improved, and it is
estimated that reportable accidents are reduced by over 80%
relative to site-intensive construction. The modules can be
installed with pre-attached protective barriers or, in some cases,
a protective “cage” is provided as part of the lifting system.
Economic Benefits of Modular Construction
Modular construction takes most of the production away from the
construction site, and essentially the slow, unproductive site activ-
ities are replaced by more efficient, faster factory processes. How-
ever, the infrastructure for factory production requires greater
investment in fixed manufacturing facilities and repeatability of
output to achieve economy of scale in production.
An economic model for modular construction must take into
account the following factors:
• Investment costs in the production facility.
• Efficiency gains in manufacture and in materials use.
• Production volume (economy of scale).
• Proportion of on-site construction (in relation to the total
build cost).
• Transport and installation costs.
• Benefits in speed of installation and reduced minor repair costs.
• Savings in site infrastructure and management (preliminaries).
Materials use and wastage are reduced and productivity is
increased, but conversely, the fixed costs of the manufacturing
facility can be as high a proportion as 20% of the total build cost.
Even in a highly modular project, a significant proportion of
additional work is done on-site. Background data may be taken
from a recent National Audit Office (NAO) report “Using Modern
Methods of Construction to Build Homes More Quickly and Effi-
ciently” (National Audit Office 2004). This report estimates that
this proportion is approximately 30% in cost terms for a fully
modular building, and may be broken down approximately into
foundations (4%), services (7%), cladding (13%), and finishing
(6%). However, in many modular projects, the proportion of on-site
work can be as high as 55% (see case study). Modular construction
also saves on commissioning and minor repair costs that can be as
high as 2% in traditional construction.
The financial benefits of speed of installation may be considered
to be:
• Reduced interest charges by the client.
• Early “start-up” of business or rental income.
• Reduced disruption to the locality or existing business.
Thesebusiness-relatedbenefitsareclearlyaffectedbythesizeand
type of the business. The tangible benefits due to reduced interest
charges can be 2 to 3% over the shorter building cycle. The NAO
report estimates that the total financial savings are as high as 5.5%.
Lessons Learned
The case studies show that modular construction can be used for
residential buildings up to 25 stories high, provided the stability
under wind action is achieved by a concrete or steel framed core.
Modules in tall buildings can be clustered around a core, or alter-
natively, they can be connected to a braced corridor, which transfers
wind-loading to the core. The design of the load-bearing walls or
corner posts should take into account the effects of eccentricities
due to manufacturing and installation tolerances.
Three case studies of modular buildings showed the different
plan forms that can be created depending on the type of modular
system. Modules with corner posts provide more flexibility in
room layouts but are more costly to manufacture than the wholly
light steel load-bearing systems. For the 25-story modular building,
the steel usage ranged from 67 to 117 kg∕m2 (14 to 24 pounds∕ft2)
floor area because the modular system had a concrete floor slab.
The modular components accounted for approximately 45% of
the completed cost of the building. The construction period was
reduced by over 50% relative to site-intensive building. Waste
was reduced by 70% on-site and most manufacturing waste was
recycled.
Conclusions
This paper shows that modular construction can be used for resi-
dential buildings up to 25 stories high, provided the stability is
achieved by a concrete or steel framed core. The structural design
of the modules is strongly influenced by installation and manufac-
turing tolerances and tying action between the modules. In terms of
layout of the modules, three modules efficiently form a two-
bedroom apartment. Modules in tall buildings can be clustered
around a core, or alternatively, they can be connected to a braced
corridor, which transfers wind-loading to the core,
Three case studies are presented of modular buildings of 12, 17,
and 25 stories in height. In the tallest building, data was collected of
the manufacturing and construction operation. For a high-rise modu-
lar building, the steel usage ranged from 67 to 117 kg∕m2 (14 to
24 pounds∕ft2) floor area depending on the floor level. The modular
components accounted for approximately 45% of the completed cost
of the building. The construction period was reduced by over 50%
JOURNAL OF ARCHITECTURAL ENGINEERING © ASCE / JUNE 2012 / 153
J. Archit. Eng. 2012.18:148-154.
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relative to site-intensive building. Waste was reduced by 70%
on-site and most manufacturing waste was recycled.
Acknowledgments
The information in this paper was provided with the assistance of
Caledonian Building Systems, Unite Modular Solutions, Vision
Modular Systems, HTA Architects and the Steel Construction
Institute, UK.
References
Cartz, J. P., and Crosby, M. (2007). “Building high-rise modular homes.”
Struct. Eng., 85(l), 20–21.
Lawson, R. M. (2007). Building design using modules, The Steel Construc-
tion Institute, Ascot, UK.
Lawson, R. M., Ogden, R. G., Pedreschi, R., Popo-Ola, S., and
Grubb, J. (2005). “Developments in prefabricated systems in
light steel and modular construction.” Struct. Eng., 83(6), 28–35.
Lawson, R. M., Byfield, M., Popo-Ola, S., and Grubb, J. (2008). “Robust-
ness of light steel frames and modular construction.” Proc. Inst. Civ.
Eng. Struct. Build., 161(1), 3–16.
Lawson, R. M., and Richards, J. (2010). “Modular design for high-
rise buildings.” Proc. Inst. Civ. Eng. Struct. Build., 163(SB3),
151–164.
Lifetime Homes Design Standard. (2010). Rowntree Foundation, York,
UK.
National Audit Office. (2004). “Using modern methods of construction to
build homes more quickly and efficiently.” London.
154 / JOURNAL OF ARCHITECTURAL ENGINEERING © ASCE / JUNE 2012
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http://dx.doi.org/10.1680/stbu.2008.161.1.3
http://dx.doi.org/10.1680/stbu.2008.161.1.3
http://dx.doi.org/10.1680/stbu.2010.163.3.151
http://dx.doi.org/10.1680/stbu.2010.163.3.151
United States Patent
US007191571B2
(12) (10) Patent No.: US 7,191,571 B2
Schools et al. (45) Date of Patent: Mar. 20, 2007
(54) MODULAR CONSTRUCTION BLOCKS, 3,782,049 A 1/1974 Sachs …………………… 52,309.9
BUILDING STRUCTURES, KITS, AND 3,878,658 A * 4, 1975 Davis et al. ……………… 52/4
10
METHODS FOR FORMING BUILDING 3,905,071 A * 9/1975 Brumlik ……………….. 24f7064
STRUCTURES 4,057,946 A 11, 1977 Barrett … 52,436
4.227.829 A * 10/1980 Landry, Jr. ………………. 405/20
(76) Inventors: Jody L. Schools, 208 Schoolhouse Rd., 4,481,155 A 1 1/1984 Frohwerk ……………….. 261.94
Stuyvesant, NY (US) 12173; Jon L. 4,492,064 A * 1/1985 Bynoe ……. … 52,309.8
Schools, 182 Fowler Lake Rd., Ghent, 4,590,729 A 5/1986 HegaZi …………………… 52/437
NY (US) 12075 4,602,908 A * 7/1986 Kroeber …………………. 446,128
4,719,738 A * 1/1988 52/6O7
(*) Notice: Subject to any disclaimer, the term of this 4,758,195 A * 7/1988 Walsh ……………………. 446,8
5
patent is extended or adjusted under 35 4,860,515 A * 8/1989 Browning, Jr. ………….. 52/426
U.S.C. 154(b) by 76 days. 4,924,641. A 5/1990 Gibbar, Jr. …….. … 52,204
5,003,746 A * 4, 1991 Wilston ………………… 52/592.1
(21) Appl. No.: 10/180,877
(22) Filed: Jun. 26, 2002 (Continued)
US 2004/0000114A1 Jan. 1, 2004 EP OOOT 630 * 1 198O
(51) Int. C
l.
Et)4C 2/26 (2006.01) (Continued)
(52) U.S. Cl. ………………………. 52/607:52/439; 52/505; Primary Examiner Winnie Yip
52/747.14 (74) Attorney, Agent, or Firm Heslin Rothenberg Farley &
(58) Field of Classification Search ………. 52/503 505, MeSiti P.C.
52/605-608, 747.12, 410, 439, 426,436,
52/309.4,404.1, 293.2, 742.14; 44.6/125, (57) ABSTRACT
446/128; 404/29, 36
See application file for complete search history.
The modular construction blocks include a preform having
(56) References Cited a plurality of passageways therethrough. The preforms may
U.S. PATENT DOCUMENTS
786,884 A 4, 1905 Faulkner
861,348 A 7, 1907 BaltZ
1,242,087 A 10, 1917 Waddell
1,524,146 A * 1/1925 Murray …………………. 52/302.4
1907,170 A * 5/1933 A Hearn ……………….. 16.5/9.1
1968,034 A * 7/1934 Ferguson . … 52,323
2,019,133 A 10/1935 Hincke …………………….. T2/
40
2,184,714. A * 12/1939 Freeman .. … 52,2
50
3,165,750 A 1, 1965 Tell ……………………….. 52,568
3,374,917 A 3/1968 Troy ……………………. 220/234
3.391,507 A * 7, 1968 Downing ………………… 52,314
by formed from a plastic material and filled with concrete
and steel reinforcing bars to form footings, foundations,
girders, walls, and roofs. The modular construction blocks
generally include a 5-hole block which has five holes or
passageways extending therethrough and a 2-hole block
which has two holes or passageways extending there
through. The 5-hole blocks include the plurality of passage
ways intersecting and extending along three different planes.
Kits, building structures, furring strips, and methods for
forming building structures are also disclosed.
43 Claims, 9 Drawing Sheets
US 7,191571 B2
Page 2
U.S. PATENT DOCUMENTS 5,839.243 A * 1 1/1998 Martin …………………… 52/439
5,987,840 A * 1 1/1999 Leppert … 52/592.6
5,351,455 A * 10/1994 Schoonover et al. ………. 52/410 6,161,357. A 12/2000 Altemus ……………….. 52/592.6
5,415,511 A * 5/1995 Damron ……… . 411/480 6.253,523 B1* 7/2001 McKinnon ………………. 52.7OO
5,457,926 A 10/1995 Jensen ….. 52,604
5,557,898 A * 9/1996 Dixon …….. 52,410 FOREIGN PATENT DOCUMENTS
5,678.378 A * 10/1997 Ellison, Jr. .. 52?692 ck
5,702.208 A * 12/1997 Hilfiker et al. 405/302.4 FR 26O7857 T 1988
5,715,635 A 2, 1998 Sherwood ……………….. 52.286 * cited by examiner
U.S. Patent Mar. 20, 2007 Sheet 1 of 9 US 7,191,571 B2
U.S. Patent Mar. 20, 2007 Sheet 2 of 9 US 7,191,571 B2
2
62
U.S. Patent Mar. 20, 2007 Sheet 3 of 9 US 7,191,571 B2
s& ŠS 110 S&aš&2S
Ssss 53.
SS
SS
Sá39 sists
100
Z ZZ GROUND
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U.S. Patent Mar. 20, 2007 Sheet 4 of 9 US 7,191,571 B2
l.
U.S. Patent Mar. 20, 2007 Sheet 5 of 9 US 7,191,571 B2
US 7,191,571 B2 Mar. 20, 2007 Sheet 6 of 9 U.S. Patent
§§§§§§) $§§ §§§§ `§>
§ §§§ * T§§ 2) 7/7
U.S. Patent Mar. 20, 2007 Sheet 7 of 9 US 7,191,571 B2
U.S. Patent Mar. 20, 2007 Sheet 8 of 9 US 7,191,571 B2
US 7,191,571 B2 9 of 9 Sheet Mar. 20, 2007 U.S. Patent
fig.
15
• … • •
• . . •
US 7, 191571 B2
1.
MODULAR CONSTRUCTION BLOCKS,
BUILDING STRUCTURES, KITS, AND
METHODS FOR FORMING BUILDING
STRUCTURES
FIELD OF THE INVENTION
This invention relates generally to bricks and building
structures, and more particularly to modular construction
blocks, building structures, kits, and methods for forming
building structures.
BACKGROUND OF THE INVENTION
Conventionally, bricks and blocks for constructing build
ing structures include solid bricks made of clay and blocks
made of concrete or cement having two chambers in the
interior of the blocks.
U.S. Pat. No. 6,161,357 issued to Altemus discloses
forming a wall with bricks formed of clay or similar mate
rials and having two or three cylindrical passageways run
ning from top to bottom, and a cylindrical passageway
running from one end to the opposite end. The passageways
are disposed in two different planes and intersect. Also, the
bricks are interlocking and may be filled with concrete and
reinforced with rods or posts.
U.S. Pat. No. 5,457,926 issued to Jensen discloses a
lightweight, non-cementitious, resilient, interlocking, plastic
foam block which can be assembled with other like blocks
to produce a light impervious wall. The foam block includes
two vertically-extending passageways. The blocks can each
be secured to abutting blocks with adhesive. Concrete and
re-bar can extend through hollows in the blocks in conven
tional fashion.
There is a need for still further modular construction
blocks, building structures, kits, and method for forming
building structures.
SUMMARY OF THE INVENTION
The present invention provides, in a first aspect, a modu
lar construction block which includes a preform having a top
Surface, a bottom surface, opposite side surfaces, and oppo
site end surfaces. The preform includes a first horizontal
passageway extending between the opposite end Surfaces, a
pair of spaced-apart vertical passageways extending from
the top Surface and intersecting the first horizontal passage
way, and a pair of spaced-apart second horizontal passage
ways extending between the opposite side Surfaces and
intersecting the first horizontal passageway and the pair of
vertical passageways.
The present invention provides, in a second aspect, a
modular construction block which includes a preform hav
ing a top, a bottom, opposite sides, and opposite ends, at
least three intersecting passageways extending through the
preform. The at least three intersecting passageways extend
along three different planes.
The present invention provides, in a third aspect, a
method for forming a floor which includes providing a first
plurality of modular construction blocks, as described
above, and a second plurality of modular construction
blocks. The second plurality of modular construction blocks
includes a preform having a top surface, a bottom Surface,
opposite side Surfaces, opposite end Surfaces, and a pair of
spaced-apart horizontal passageways extending between the
opposite side surfaces. At least one row of the first plurality
of modular construction blocks is assembled in the second
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plurality of assembled modular construction blocks to define
a girder. Thereafter, concrete is introduced into the passage
ways in the first and second plurality of modular construc
tion blocks.
The present invention provides, in a fourth aspect, a
method for forming a footing and a foundation. The method
includes assembling a first plurality of modular construction
blocks, as described above, end to end to form a perimeter
of the foundation, and assembling a second plurality of
modular construction blocks in the footing to form the
foundation. The second plurality of modular construction
blocks includes a preform having a top Surface, a bottom
Surface, opposite side Surfaces, and opposite end Surfaces,
and a pair of spaced-apart horizontal passageways extending
between the opposite side surfaces. Concrete is then intro
duced into the passageways in the first and second plurality
of modular construction blocks so that the concrete in the
perimeter forms a grid pattern.
The present invention provides, in a fifth aspect, a method
for forming a floor which includes assembling a plurality of
modular construction blocks comprising a preform having a
top Surface, a bottom Surface, opposite side surfaces, and
opposite end Surfaces. The preform includes a pair of
spaced-apart horizontal passageways extending between the
opposite side Surfaces. Some of the passageways are opened
to the top to form a trough. Thereafter, concrete is introduced
into the passageways and troughs of the assembled plurality
of modular construction blocks.
The present invention provides, in a sixth aspect, a furring
strip for use with modular construction blocks having pas
sageways which are assembled and filled with concrete. The
furring strip includes an elongated member and a plurality of
elongated anchors attachable to the elongated member. The
elongated members have a plurality of outwardly-extending
portions for engaging the modular construction block and
for extending into the passageways.
The present invention provides, in a seventh aspect, a
method for forming a wall which includes assembling a
plurality of modular construction blocks comprising a pre
form having a top Surface, a bottom surface, opposite side
Surfaces, opposite end Surfaces, and a pair of spaced-apart
vertical passageways extending between the top and bottom
Surfaces. A plurality of furring strips are installed against the
assembled blocks. The plurality of furring strips comprise an
elongated member and a plurality of elongated anchors
attachable to the elongated member. The elongated member
has a plurality of outwardly-extending portions for engaging
the modular construction block and extending into the
passageways. Thereafter, concrete is introduced into the
passageways of the assembled plurality of modular con
struction blocks so a portion of the plurality of anchors is
secured in the concrete.
Also, disclosed are kits comprising the various blocks and
furring strips.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the con
cluding portion of the specification. The invention, however,
may best be understood by reference to the following
detailed description of various embodiments and accompa
nying drawings in which:
FIG. 1 is a perspective view of a first modular construc
tion block in accordance with the present invention;
FIG. 2 is an enlarged sectional view of the first modular
construction block taken along each of lines 2–2 in FIG. 1;
US 7, 191571 B2
3
FIG. 3 is a perspective view of a second modular con
struction block in accordance with the present invention;
FIG. 4 is an enlarged sectional view of the second
modular construction block taken along each of lines 4-4
in FIG. 3;
FIG. 5 is a perspective view of a footing, foundation, and
girder formed using the modular construction blocks shown
in FIGS. 1 and 3;
FIG. 6 is a sectional view of the footing and foundation
of FIG. 5 taken along line 6–6 in FIG. 5;
FIG. 7 is a sectional view of the first modular construction
block of FIG. 1 along with a plug in accordance with the
present invention;
FIG. 8 is a perspective view of a third modular construc
tion block in accordance with the present invention;
FIG. 9 is an enlarged sectional view of the third modular
construction block taken along each of lines 9–9 in FIG. 8:
FIG. 10 is a perspective view of a construction of a
building in accordance with the present invention using the
blocks of FIGS. 1, 3, and 9:
FIG. 11 is a perspective view of a fourth modular con
struction block in accordance with the present invention;
FIG. 12 is a sectional view of the fourth modular con
struction block taken along each of lines 12–12 in FIG. 11;
FIG. 13 is a perspective view of a floor formed using the
modular construction blocks shown in FIG. 11 and in which
portions of the blocks have been removed to provide troughs
for added strength;
FIG. 14 is a perspective view of floor having an I-bean
formed in accordance with the present invention;
FIG. 15 is a perspective view of a furring strip in
accordance with the present invention; and
FIG.16 is a sectional view of a wall formed from modular
construction blocks to which the furring strips of FIG. 15 is
attached.
DETAILED DESCRIPTION OF THE
INVENTION
FIGS. 1, 3, 8, and 11 illustrate modular construction
blocks in accordance with the present invention. As illus
trated in FIGS. 1, 3, 8, and 11, the blocks include a preform
and a plurality of passageways therethrough. The preforms
may by formed from a plastic material and used by assem
bling and filling with concrete and steel reinforcing bars to
form footings, foundations, girders, walls, and roofs. The
modular construction blocks generally include a 5-hole
block (and modified 5-hole block) which includes five holes
or passageways extending therethrough and a 2-hole block
(and modified 2-hole block) which includes two holes or
passageways extending therethrough. As described in
greater detail below, the combination of 5-hole blocks and
2-hole blocks results in forming reinforced cement or con
crete within the blocks which has an interlocking grid
configuration in one plane or axis, two planes or axes (e.g.,
wall and floor), and/or three planes or axes (e.g., floor, wall,
and roof which strengthens the building structure.
With reference to FIGS. 1 and 2, a 5-hole modular
construction block 10 generally includes a preform 20
having a top surface 21, a bottom surface 22 (FIG. 2),
opposite side surfaces 23 and 24 (FIG. 2), and opposite end
surfaces 25 (only one end surface being shown in FIG. 1).
A plurality of passageways extends through the preform.
For example, the plurality of passageways intersects and
extends along three different planes. As illustrated in FIGS.
1 and 2, a first horizontally-extending passageway 30
extends between and opens onto each of the opposite end
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Surfaces. A pair of spaced-apart vertically-extending pas
sageways 32 extends between and opens onto top surface 21
and bottom surface 22 (FIG. 2) and intersects first horizon
tally-extending passageway 30. A pair of spaced-apart sec
ond horizontally-extending passageways 34 extends
between and opens onto the opposite side Surfaces 23 and 24
and intersects first horizontally-extending passageway 30
and the pair of vertically-extending passageways 32.
With reference to FIGS. 3 and 4, a 2-hole modular
construction block 50 generally includes a preform 60
having a top surface 61, a bottom surface 62 (FIG. 4),
opposite side surfaces 63 and 64 (FIG. 4), and opposite end
surfaces 65 (only one end surface shown in FIG. 3). As
illustrated in FIGS. 3 and 4, a pair of spaced-apart second
horizontally-extending passageways 74 extends between
and opens onto the opposite side surfaces 63 and 64 (FIG.
4).
The blocks may also be provided with interlocking por
tions to aid in aligning and maintaining the blocks in
position when assembled or stacked together. For example,
the top Surface and the bottom Surface, the opposite side
Surfaces, and the opposite end Surfaces may each include
interlocking portions. FIGS. 1 and 3 illustrate one example
of interlocking portions which includes indentations 40
disposed on side surface 23 of block 10 (and side surface 24
may include corresponding raised projections, not shown in
FIG. 1). FIG. 3 illustrates an example of raised projections
80 disposed on surface 63 of block 50. It will be appreciated
that the opposite surfaces, top Surfaces, bottom Surfaces, and
end Surfaces may also be provided with interlocking por
tions. When the blocks are assembled and/or stacked
together, the ends of adjacent blocks may be staggered.
With reference still to FIGS. 1 and 3, the indentations and
projections provide alignment in two directions or planes,
e.g., up and down, and side-to-side. It will be appreciated
that the raised portions and indentations may include other
configurations such as raised and indented squares or circles.
In addition, the raised portion and indentations may extend
completely along the length or width of the block or around
the openings. Other suitable interlocking portions for use
with the blocks of the present invention are disclosed in U.S.
Pat. No. 6,161,357 issued to Altemus, and U.S. Pat. No.
5,457.926 issued to Jensen. The entire subject matter of
these patents is incorporated herein by reference.
FIGS. 5 and 6 illustrate a foundation 100 constructed
using a plurality of blocks 10 and 50. A footing 110 of
foundation 100 is constructed by stacking two rows of
5-hole blocks 10 in a standard run to form the perimeter of
the foundation and laying a plurality of 2-hole blocks 50
within the perimeter. At intervals in the floor, two rows of
5-hole blocks 10 may be installed to form a girder 120 (FIG.
5). The blocks may be initially assembled and held together
using an adhesive such as 3M’s SUPER 77 adhesive.
With reference to FIG. 7, plugs 140 (only one of which is
shown in FIG. 7) may have a slight taper and used to seal the
bottom vertical opening in the blocks. The plugs may also be
held and fastened to the block using an adhesive. The top
openings which will be filled with concrete provide a solid
structure for attachment or securing fasteners.
Steel reinforcement, for example, steel reinforcing bars
142 may be inserted into the blocks forming the foundation.
Suitable spacer clips 144 and 146 may be used to support
and maintain the steel reinforcing bars in the proper location
within the blocks when introducing the concrete. As shown
FIG. 7, spacer clips 144 and 146 may be a wire or plastic
form having one or portions which engage one or more
US 7, 191571 B2
5
reinforcing rods. The ends of the clips may be sized to
engage the inner Surface of the passageways.
FIGS. 8 and 9 illustrate a modified 5-hole modular
construction block 200. Block 200 may be used for footing,
headers, and girders, and avoid the need for attaching plugs
to the bottom openings. Block 200 generally includes a
preform 220 having a top surface 221, a bottom surface 222
(FIG. 9), opposite side surfaces 223 and 224 (FIG. 9), and
opposite end Surfaces 225 (only one end Surface shown in
FIG. 8).
A plurality of passageways extends through the preform.
For example, the plurality of passageways intersects and
extends along three different planes. As illustrated in FIGS.
8 and 9, a first horizontally-extending passageway 230
extends between and opens onto each of the opposite end
Surfaces. A pair of spaced-apart vertically-extending pas
sageways 232 extends between top Surface 221 and opens
into first horizontally-extending passageway 230 and do not
extend onto bottom surface 222 as shown in FIG. 9. A pair
of spaced-apart second horizontally-extending passageways
234 extends between and opens onto the opposite side
surfaces 223 and 224 and intersects first horizontally-ex
tending passageway 230 and the pair of vertically-extending
passageways 232.
Blocks 10, 50, and 200 may be formed from plastic or
polymeric material Such as a foam plastic material. Such
foam plastic materials may include dense polystyrene foam.
The blocks may also include recycled materials, or combi
nations of Virgin and recycled materials. It is also appreci
ated that the preforms may be formed from concrete, or
cement or clay and used in forming hollow building struc
tures or filled with cement and reinforcing bars.
The blocks may include the top surface, the bottom
Surface, and the opposite side Surfaces defining a square
cross-section, and the top surface, the bottom Surface, and
the opposite end Surfaces may define a rectangular cross
section. For example, the blocks may be 24 inches long, 12
inches high, 12 inches wide, and the passageways may be
cylindrical having a diameter of 6 inches. It will be appre
ciated that the blocks may be formed in other sizes and the
passageways may have other configurations other than
cylindrical. While the blocks have been described as having
a top Surface and bottom Surface, it will also be appreciated
that depending on the orientation of the block, the opposite
side Surfaces may be the top and bottom Surfaces.
With reference again to FIG. 5, once the blocks are
assembled and the reinforcing bars installed, holes 130 (only
one of which is shown in FIG. 5) are cut in the center of the
floor. Concrete may then be injected, using a tapered hose
end which fits tightly in the hole. Alternatively, the concrete
may be injected through the vertical openings in girder 120.
The concrete may be a lightweight concrete and may incor
porate recycled materials to increase strength and/or reduce
weight. The concrete may be driven by a commercial
concrete pump which Supplies Sufficient pressure to cause
the concrete to flow through the passageways. When con
crete is visible in the blocks forming the footing, the hose is
removed, and the hole is sealed with a plug. Thereafter, the
blocks forming the footing are filled with concrete.
FIG. 10 illustrates a wall 300 formed by stacking 2-hole
blocks on the footing with the passageways therein disposed
vertically. As discussed above, an adhesive may be used to
hold the blocks in place. Doors headers (not shown) and
window headers 310 (only one being shown in FIG. 10) are
formed by stacking 2-hole blocks from the footing to the top
of the desired window or door opening. Two rows of the
5-hole blocks, the lowermost vertical openings being
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plugged or the lower row of blocks being the modified
5-hole blocks, are then stacked to bridge the openings. Steal
reinforcing bars may be inserted in the blocks. Thereafter,
concrete can be injected into the passageways. Air vent holes
may be required to allow the release of air when injecting the
concrete into the walls.
Subsequent floors 320, as well as roofs 340, may require
scaffolding in order to install and support the blocks when
introducing the concrete as described above. Forming of
roofs may also require cutting air vent holes prior to inject
ing the concrete into the blocks forming the roof.
Where the wall and roof intersect, both the top block of
the wall and the lower blocks of the roof may be cut on an
angle (e.g., /2 the pitch of the roof) to intersect so that the
openings of the passageways align and through which the
reinforcing bar and concrete can be introduced. Such a
configuration forms a continuous joint along the intersection
of the wall and roof.
FIGS. 11 and 12 illustrate a modified 2-hole block 400 in
which top portions of the block have been removed to open
and expose the horizontally-extending passageway to define
and form a trough 474. When used in the floor or foundation,
the removed portions are filled to the top of the blocks with
concrete (and reinforcing bar) to strengthen the floor along
a horizontal plane compared to the floor shown in FIG. 5.
The increased strength may allow a floor to have a greater
span between Supports, columns, or bearing walls. While the
modified 2-hole block may include removal of two portions,
specific portions may be selected and removed, for example,
on site. For example, FIG. 13 illustrates a floor 500 which
includes alternating portions of the 2-hole blocks having
portions removed. It will be appreciated that where added
strength is needed, the two-hole blocks may be formed with
troughs by a manufacturer, cut prior to assembly, or cut after
assembly, and then filled with concrete and reinforcing bars.
In addition, an I-beam may be formed into a floor using
blocks of the present invention. As shown in FIG. 14, a floor
I-beam 600 may be formed by two stacked rows of 5-hole
blocks. The block disposed below the floor may be provided
with plugs on each of the lateral sides and bottom. Such a
configuration may result in floors with greater spans or
reduced need for Support columns.
The footings, girders, and headers, I-beams being formed
with the 5-hole blocks provide a grid, a lattice, or a criss
crossing and interconnecting pattern (e.g., ladder on side)
resulting in added strength. In addition, footings formed
with the 5-hole blocks have a grid in one plane which is
connected the floor disposed in a second plane. Use of the
modular construction blocks of the present invention results
added strength to the structure in that the entire structure
may be formed with a concrete and steel reinforced locked
in web or cage due to the grid formations resulting form
assembly of the various blocks. In addition, the intersection
of for example, a wall to a floor, or a wall to a roof may be
provided with two rows of 5-hole blocks to provide a grid in
one or more planes.
The walls, floors, foundations, footings, and roofs may be
covered with a suitable covering material Such as plaster,
stucco or other suitable material. Sheetrock may be glued to
the inside of walls and floors may be glued in place. Radiant
heat may be bonded to the floor before securing a finished
floor above.
FIG. 15 illustrates a surface fastener or furring strip 700
for use in attaching other types of interior or exterior
surfacing to the assembled blocks. Furring strip 700 gener
ally includes an elongated member 710 and a plurality of
anchors 720. Prior to introducing concrete into the various
US 7, 191571 B2
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passageways in, for example a wall as shown in FIG. 16, a
plurality of spaced-apart furring strips 700 may be posi
tioned against the wall with the anchors pushed through the
foam blocks. An end portion 722 of the anchors 720 may
have outwardly extending portions such as spikes or barbs
which attach and anchor to the concrete when cured, while
the middle portion 724 may have outwardly extending
portions such as spikes or barbs which engage and are
retained in the foam portion of a block prior to the concrete
being poured. Various finishing Surfaces such as wood
framing can be attached to the elongated member 710. The
elongated member may be made from wood or plastic and
may be sized three inches wide and 1/4 inches thick.
Such structures formed in accordance with the invention
may be better able to withstand winds, tornados, or other
natural forces. In addition, a structure Such as a building may
be formed or manufactured at a central or manufacturing
site, and due to its grid-like interconnection of the concrete
and reinforced bars, may be lifted and transported to a
remote site for use. While the entire structure may be
assembled and transported, Smaller sections or portions may
also be assembled and transported with final assembly at a
desired location. For transporting, one or more attachment
points such as attachment hooks or eyes may be incorpo
rated into the structure to allow the structure to be lifted and
transported. In addition, the building structure may be
configured and include suitable devices to allow the struc
ture to be buoyant, and thus, float in a body of water such as
a lake or river. It will also be appreciated by those skilled in
the art that various sizes of the blocks may be used. For
example, for a shed, six inch blocks having three inch
diameter passageways may be used.
Thus, while various embodiments of the present invention
have been illustrated and described, it will be appreciated to
those skilled in the art that many changes and modifications
may be made thereunto without departing from the spirit and
Scope of the invention.
The invention claimed is:
1. A modular construction block comprising:
a preform having a top Surface, a bottom surface, opposite
side Surfaces, and opposite end Surfaces; and
said preform having;
a first horizontal passageway extending between said
opposite end Surfaces, said first horizontal passage
way defining openings on said opposite end Surfaces
spaced from said top Surface, said bottom Surface
and said opposite side Surfaces;
a pair of spaced-apart vertical passageways extending
from said top Surface to said bottom Surface and
intersecting said first horizontal passageway, said
pair of spaced-apart vertical passageways defining
openings on said top surface and said bottom Surface
spaced from said opposite side surfaces and said
opposite end Surfaces;
a pair of spaced-apart second horizontal passageways
extending between said opposite side Surfaces and
intersecting said first horizontal passageway and said
pair of vertical passageways, said pair of spaced
apart second horizontal passageways defining open
ings on said opposite side Surfaces spaced from said
top Surface, said bottom Surface, and said opposite
end Surfaces; and
wherein said preform comprises a foam material.
2. The modular construction block of claim 1 wherein
cross-sections of the passageways are the same.
3. The modular construction block of claim 1 wherein at
least one of said top surface and said bottom Surface, said
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opposite side Surfaces, and said opposite end Surfaces com
prise interlocking portions for engaging adjacent modular
construction blocks.
4. The modular construction block of claim 1 wherein said
preform comprises a plastic foam material.
5. A building structure comprising:
a plurality of modular construction blocks of claim 1.
6. The building structure of claim 5 wherein the modular
blocks are assembled and filled with concrete to form a
reinforced grid pattern in at least two planes.
7. The building structure of claim 5 wherein the modular
blocks are assembled and filled with concrete to form a
reinforced grid pattern in three planes.
8. A kit for forming a building structure comprising:
a first plurality of modular construction blocks of claim 1:
and
a second plurality of modular construction blocks com
prising a preform having a top surface, a bottom
Surface, opposite side Surfaces, opposite end Surfaces,
and a pair of spaced-apart passageways extending
between said opposite side Surfaces.
9. The kit of claim 8 further comprising a plurality of
plugs for sealing openings formed by said passageways.
10. The kit of claim 8 further comprising a plurality of
furring strips comprising an elongated member and a plu
rality of anchors.
11. The kit of claim 8 wherein cross-sections of the
passageways are the same.
12. A method for forming a floor comprising:
providing a first plurality of modular construction blocks
of claim 1:
providing a second plurality of modular construction
blocks comprising a preform having a top surface, a
bottom Surface, opposite side Surfaces, opposite end
Surfaces, and a pair of spaced-apart horizontal passage
ways extending between the opposite side surfaces:
assembling at least one row of the first plurality of
modular construction blocks within the second plural
ity of modular construction blocks to define a girder;
and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the first plurality of modular construc
tion blocks forms the girder.
13. A method for forming a footing and a foundation, the
method comprising:
assembling a first plurality of modular construction blocks
of claim 1 end to end to form a perimeter of the
foundation;
assembling a second plurality of modular construction
blocks within the footing to form the foundation, the
second modular construction blocks comprising a pre
form having a top Surface, a bottom surface, opposite
side Surfaces, opposite end Surfaces, and a pair of
spaced-apart horizontal passageways extending
between the opposite side Surfaces; and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the perimeter forms a grid pattern.
14. The method of claim 13 further comprising assem
bling at least one row of the first plurality of modular
construction blocks within the foundation to form a girder.
15. The method of claim 13 further comprising inserting
a plurality of plugs in the openings of the plurality of blocks.
16. The modular construction block of claim 1 wherein
said preform comprises a length of about 24 inches, a height
of about 12 inches, and a width of about 12 inches.
US 7, 191571 B2
17. A modular construction block comprising:
a preform having a top, a bottom, opposite sides, and
opposite ends;
at least three intersecting passageways extending through
said preform;
said at least three intersecting passageways extending
along three different planes;
a first of said at least three intersecting passageways
defining openings on said opposite ends spaced from
said top, said bottom, and said opposite sides;
a second of said at least three intersecting passageways
defining an opening on said top spaced from said
opposite sides and said opposite ends;
a third of said at least three intersecting passageways
defining openings on said opposite sides spaced from
said top, said bottom, and said opposite ends; and
wherein said preform comprises a foam material.
18. The modular construction block of claim 17 wherein
at least one of said top surface and said bottom surface, said
opposite side Surfaces, and said opposite end Surfaces com
prise interlocking portions for engaging adjacent modular
construction blocks.
19. The modular construction block of claim 17 wherein
said preform comprises a plastic foam material.
20. A building structure comprising:
a plurality of modular construction blocks of claim 17.
21. The building structure of claim 20 wherein the modu
lar blocks are assembled and filled with concrete to form a
reinforced grid pattern in at least two planes.
22. The building structure of claim 20 wherein the modu
lar blocks are assembled and filled with concrete to form a
reinforced grid pattern in three planes.
23. A kit for forming a building structure comprising:
a first plurality of modular construction blocks of claim
17; and
a second plurality of modular construction blocks com
prising a preform having a top surface, a bottom
Surface, opposite side Surfaces, opposite end Surfaces,
and a pair of spaced-apart passageways extending
between said opposite side Surfaces.
24. The kit of claim 23 further comprising a plurality of
plugs for sealing openings formed by said passageways.
25. The kit of claim 23 further comprising a plurality of
furring strips comprising an elongated member and a plu
rality of anchors.
26. The kit of claim 23 wherein cross-sections of the
passageways are the same.
27. A method for forming a floor comprising:
providing a first plurality of modular construction blocks
of claim 17:
providing a second plurality of modular construction
blocks comprising a preform having a top surface, a
bottom Surface, opposite side Surfaces, opposite end
Surfaces, and a pair of spaced-apart horizontal passage
ways extending between the opposite side Surfaces;
assembling at least one row of the first plurality of
modular construction blocks within the second plural
ity of modular construction blocks to define a girder;
and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the first plurality of modular construc
tion blocks forms the girder.
28. A method for forming a footing and a foundation, the
method comprising:
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assembling a first plurality of modular construction blocks
of claim 17 end to end to form a perimeter of the
foundation;
assembling a plurality of second modular construction
blocks within the footing to form the foundation, the
second modular construction blocks comprising a pre
form having a top Surface, a bottom surface, opposite
side Surfaces, opposite end Surfaces, and a pair of
spaced-apart horizontal passageways extending
between the opposite side Surfaces; and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the perimeter forms a grid pattern.
29. The method of claim 28 further comprising assem
bling at least one row of the first plurality of modular
construction blocks within the foundation to define a girder.
30. The method of claim 29 further comprising inserting
a plurality of plugs in the openings of the plurality of blocks.
31. A method for forming a wall, the method comprising:
assembling a plurality of modular construction blocks of
claim 17:
installing a plurality of furring strips against the
assembled blocks, the plurality of furring strips com
prising an elongated member, and a plurality of elon
gated anchors attachable to the elongated member and
having an elongated portion extendable through said
modular construction blocks and into said passage
ways, said elongated portion having at least one out
wardly-extending portion for engaging the modular
construction block and at least one outwardly extending
portion extending into the passageways, and wherein
the at least one outwardly-extending portions comprise
barbs; and
introducing concrete into the passageways of the
assembled plurality of modular construction blocks so
a portion of the plurality of anchors is secured in the
COncrete.
32. The modular construction block of claim 17 wherein
said preform comprises a length of about 24 inches, a height
of about 12 inches, and a width of about 12 inches.
33. A kit for forming a building structure comprising:
a first plurality of modular construction blocks comprising
a preform having a top Surface, a bottom Surface,
opposite side Surfaces, and opposite end Surfaces; and
said preform having;
a first horizontal passageway extending between said
opposite end Surfaces, said first horizontal passage
way defining openings on said opposite end Surfaces
spaced from said top surface, said bottom Surface,
and said opposite side Surfaces;
a pair of spaced-apart vertical passageways extending
from said top surface and intersecting said first
horizontal passageway, said pair of spaced-apart
vertical passageways defining openings on said top
Surface spaced from said opposite side Surfaces and
said opposite end Surfaces; and
a pair of spaced-apart second horizontal passageways
extending between said opposite side Surfaces and
intersecting said first horizontal passageway and said
pair of vertical passageway, said pair of spaced-apart
second horizontal passageways defining openings on
said opposite side Surfaces spaced from said top
Surface, said bottom surface, and said opposite end
Surfaces;
a second plurality of modular construction blocks com
prising a preform having a top surface, a bottom
Surface, opposite side Surfaces, opposite end Surfaces,
US 7, 191571 B2
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and a pair of spaced-apart passageways extending
between said opposite side Surfaces; and
a plurality of plugs for sealing openings formed by said
passagewayS.
34. A kit for forming a building structure comprising:
a first plurality of modular construction blocks comprising
a preform having a top Surface, a bottom Surface,
opposite side Surfaces, and opposite end Surfaces; and
said preform having;
a first horizontal passageway extending between said
opposite end Surfaces, said first horizontal passage
way defining openings on said opposite end Surfaces
spaced from said top Surface, said bottom Surface
and said opposite side Surfaces;
a pair of spaced-apart vertical passageways extending
from said top surface and intersecting said first
horizontal passageway, said pair of spaced-apart
vertical passageways defining openings on said top
Surface spaced from said opposite side Surfaces and
said opposite end Surfaces; and
a pair of spaced-apart second horizontal passageways
extending between said opposite side Surfaces and
intersecting said first horizontal passageway and said
pair of vertical passageway, said pair of spaced-apart
second horizontal passageways defining openings on
said opposite side Surfaces spaced from said top
Surface, said bottom surface, and said opposite end
Surfaces;
a second plurality of modular construction blocks com
prising a preform having a top surface, a bottom
Surface, opposite side Surfaces, opposite end Surfaces,
and a pair of spaced-apart passageways extending
between said opposite side Surfaces; and
a plurality of furring strips comprising an elongated
member and a plurality of anchors comprising barbs.
35. A kit for forming a building structure comprising:
a first plurality of modular construction blocks compris
1ng:
a preform having a top, a bottom, opposite sides, and
opposite ends;
at least three intersecting passageways extending
through said preform;
wherein said at least three intersecting passageways
extend along three different planes;
a first of said at least three intersecting passageways
defining openings on said opposite ends spaced from
said top, said bottom and said opposite sides;
a second of said at least three intersecting passageways
defining an opening on said top spaced from said
opposite sides and said opposite ends; and
a third of said at least three intersecting passageways
defining openings on said opposite sides spaced from
said top, said bottom, and said opposite ends;
a second plurality of modular construction blocks com
prising a preform having a top surface, a bottom
Surface, opposite side Surfaces, opposite end Surfaces,
and a pair of spaced-apart passageways extending
between said opposite side Surfaces; and
a plurality of plugs for sealing openings formed by said
passagewayS.
36. A kit for forming a building structure comprising:
a first plurality of modular construction blocks compris
1ng:
a preform having a top, a bottom, opposite sides, and
opposite ends;
at least three intersecting passageways extending
through said preform;
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wherein said at least three intersecting passageways
extend along three different planes;
a first of said at least three intersecting passageways
defining openings on said opposite ends spaced from
said top, said bottom and said opposite sides;
a second of said at least three intersecting passageways
defining an opening on said top spaced from said
opposite sides and said opposite ends; and
a third of said at least three intersecting passageways
defining openings on said opposite sides spaced from
said top, said bottom, and said opposite ends;
a second plurality of modular construction blocks com
prising a preform having a top surface, a bottom
Surface, opposite side Surfaces, opposite end Surfaces,
and a pair of spaced-apart passageways extending
between said opposite side Surfaces; and
a plurality of furring strips comprising an elongated
member and a plurality of anchors comprising barbs.
37. A method for forming a floor comprising:
providing a first plurality of modular construction blocks
comprising a preform comprising a foam material and
having a top surface, a bottom Surface, opposite side
Surfaces, and opposite end Surfaces; and
said preform having;
a first horizontal passageway extending between said
opposite end Surfaces, said first horizontal pas
sageway defining openings on said opposite end
Surfaces spaced from said top surface, said bottom
Surface and said opposite side Surfaces:
a pair of spaced-apart vertical passageways extend
ing from said top surface and intersecting said first
horizontal passageway, said pair of spaced-apart
Vertical passageways defining openings on said
top Surface spaced from said opposite side Sur
faces and said opposite end Surfaces; and
a pair of spaced-apart second horizontal passage
ways extending between said opposite side Sur
faces and intersecting said first horizontal pas
sageway and said pair of vertical passageways,
said pair of spaced-apart second horizontal pas
sageways defining openings on said opposite side
Surfaces spaced from said top surface, said bottom
Surface, and said opposite end Surfaces;
providing a second plurality of modular construction
blocks comprising a preform comprising a foam mate
rial and having a top surface, a bottom Surface, opposite
side Surfaces, opposite end Surfaces, and a pair of
spaced-apart horizontal passageways extending
between the opposite side Surfaces;
assembling at least one row of the first plurality of
modular construction blocks in the second plurality of
modular construction blocks to define a girder, and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the first plurality of modular construc
tion blocks forms the girder.
38. A method for forming a floor comprising:
providing a first plurality of modular construction blocks
comprising:
a preform comprising a foam material and having a top,
a bottom, opposite sides, and opposite ends;
at least three intersecting passageways extending
through said preform;
wherein said at least three intersecting passageways
extend along three different planes;
US 7, 191571 B2
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a first of said at least three intersecting passageways
defining openings on said opposite ends spaced from
said top, said bottom and said opposite sides;
a second of said at least three intersecting passageways
defining an opening on said top spaced from said
opposite sides and said opposite ends; and
a third of said at least three intersecting passageways
defining openings on said opposite sides spaced from
said top, said bottom, and said opposite ends;
providing a second plurality of modular construction
blocks comprising a preform comprising a foam mate
rial and having a top surface, a bottom surface, opposite
side surfaces, opposite end surfaces, and a pair of
spaced-apart horizontal passageways extending
between the opposite side surfaces:
assembling at least one row of the first plurality of
modular construction blocks within the second plural
ity of modular construction blocks to define a girder;
and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the first plurality of modular construc
tion blocks form the girder.
39. A method for forming a footing and a foundation, the
method comprising:
assembling a first plurality of modular construction blocks
end to end to form a perimeter of the foundation, the
first plurality of blocks comprising a preform having a
top surface, a bottom surface, opposite side surfaces,
and opposite end surfaces; and
said preform comprising a foam material and having:
a first horizontal passageway extending between said
opposite end surfaces, said first horizontal pas
sageway defining openings on said opposite end
surfaces spaced from said top surface, said bottom
surface and said opposite side surfaces:
a pair of spaced-apart vertical passageways extend
ing from said top surface and intersecting said first
horizontal passageway, said pair of spaced-apart
vertical passageways defining openings on said
top surface spaced from said opposite side Sur
faces and said opposite end surfaces; and
a pair of spaced-apart second horizontal passage
ways extending between said opposite side Sur
faces and intersecting said first horizontal pas
sageway and said pair of vertical passageway, said
pair of spaced-apart second horizontal passage
ways defining openings on said opposite side
surfaces spaced from said top surface, said bottom
surface, and said opposite end surfaces:
assembling a second plurality of modular construction
blocks within the footing to form the foundation, the
second modular construction blocks comprising a pre
form comprising a foam material and having a top
surface, a bottom surface, opposite side surfaces, oppo
site end surfaces, and a pair of spaced-apart horizontal
passageways extending between the opposite side Sur
faces; and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the perimeter forms a grid pattern.
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40. A method for forming a footing and a foundation, the
method comprising:
assembling a first plurality of modular construction blocks
end to end to form a perimeter of the foundation, the
first plurality of modular construction blocks compris
1ng:
a preform comprising a foam material and having a top.
a bottom, opposite sides, and opposite ends;
at least three intersecting passageways extending
through said preform:
wherein said at least three intersecting passageways
extend along three different planes;
a first of said at least three intersecting passageways
defining openings on said opposite ends spaced from
said top, said bottom and said opposite sides;
a second of said at least three intersecting passageways
defining an openings on said top spaced from said
opposite sides and said opposite ends; and
a third of said at least three intersecting passageways
defining openings on said opposite sides spaced from
said top, said bottom, and said opposite ends;
assembling a plurality of second modular construction
blocks within the footing to form the foundation, the
second modular construction blocks comprising a pre
form comprising a foam material and having a top
surface, a bottom surface, opposite side surfaces, oppo
site end surfaces, and a pair of spaced-apart horizontal
passageways extending between the opposite side Sur
faces; and
introducing concrete into the passageways in the first and
second plurality of modular construction blocks so that
the concrete in the perimeter forms a grid pattern.
41. A method for forming a building structure, the method
comprising:
providing a plurality of preforms comprising a foam
material and having a top, a bottom, opposite sides, and
opposite ends, and at least three intersecting passage
ways extending through said perform, a first of said at
least three intersecting passageways defining openings
on said opposite ends spaced from said top, said bottom
and said opposite sides, a second of said at least three
intersecting passageways defining an opening on said
top spaced from said opposite sides and said opposite
ends, and a third of said at least three intersecting
passageways defining openings on said opposite sides
spaced from said top, said bottom, and said opposite
ends;
assembling the plurality of preforms into three different
planes; and
introducing concrete into the passageways of the plurality
of preforms to form a grid pattern along three different
planes.
42. The method of claim 41 wherein said plurality of
preforms comprise portions of a wall, portions of a floor, and
portions of a roof.
43. The method of claim 41 wherein said plurality of
preforms comprise portions of a first wall, portions of a
second wall, and portions of a floor.
ck ck ck ck ck
Case Study
Application of Modular Construction
in High-Rise Buildings
R. Mark Lawson, M.ASCE1; Ray G. Ogden2; and Rory Bergin3
Abstract: Modular construction is widely used in Europe for multi-story residential buildings. A review of modular technologies is
presented, which shows how the basic cellular approach in modular construction may be applied to a wide range of building forms
and heights. Case studies on 12-, 17-, and 25-story modular buildings give design and constructional information for these relatively tall
buildings. The case studies also show how the structural action of modular systems affects the architectural design concept of the building.
The combination of modules with steel or concrete frames increases the range of design opportunities, particularly for mixed-use commercial
and residential buildings. An overview of the sustainability benefits and economics of modular construction is presented based on these
case studies. DOI: 10.1061/(ASCE)AE.1943-5568.0000057. © 2012 American Society of Civil Engineers.
CE Database subject headings: High-rise buildings; Residential buildings; Construction; Economic factors; Europe; Methodology.
Author keywords: Modular; Steel; Residential; High-rise; Construction; Economics.
Introduction
Modular construction comprises prefabricated room-sized volu-
metric units that are normally fully fitted out in manufacture
and are installed on-site as load-bearing “building blocks.” Their
primary advantages are:
• Economy of scale in manufacturing of multiple repeated units,
• Speed of installation on-site, and
• Improved quality and accuracy in manufacture.
Potentially, modular buildings can also be dismantled and re-
used, thereby effectively maintaining their asset value. The current
range of applications of modular construction is in cellular-type
buildings such as hotels, student residences, military accommoda-
tions, and social housing, where the module size is compatible with
manufacturing and transportation requirements. The current appli-
cation of modular construction of all types is reviewed in a recent
Steel Construction Institute publication (Lawson 2007). Lawson
et al. (2005) describe the mixed use of modules, panels, and steel
frames to create more adaptable building forms.
There are two generic forms of modular construction in steel,
which affects their range of application and the building forms that
can be designed:
• Load-bearing modules, in which loads are transferred through
the side walls of the modules.
• Corner-supported modules, in which loads are transferred via
edge beams to corner posts (see Fig. 1).
In the first case, the compression resistance of the walls (gen-
erally comprising light steel C-sections at 300 to 600 mm spacing)
is the controlling factor. The double layer walls and floor/ceiling
combination enhances the acoustic insulation and fire resistance
of the construction system.
In the second case, the compression resistance of the corner
posts is the controlling factor and for this reason, square hollow
sections (SHS) are often used due to their high buckling resistance.
Resistance to horizontal forces, such as wind loads and robust-
ness to accidental actions, become increasingly important with the
scale of the building. The strategies employed to ensure adequate
stability of modular assemblies, as a function of the building
height, are:
• Diaphragm action of boards or bracing within the walls of the
modules–suitable for 4- to 6-story buildings.
• Separate braced structure using hot-rolled steel members lo-
cated in the lifts and stair area or in the end gables—suitable
for 6- to 10-stories.
• Reinforced concrete or steel core–suitable for taller buildings.
Modules are tied at their corners so that structurally they act
together to transfer wind loads and to provide for alternative load
paths in the event of one module being severely damaged. For taller
buildings, questions of compression resistance and overall stability
require a deeper understanding of the behavior of the light steel
C-sections in load-bearing walls and of the robust performance
of the interconnection between the modules.
Modular Construction in High-Rise Residential
Buildings
Spatial Arrangement of the Modules
Designing with modular construction is not a barrier to creativity.
Modular rooms or pairs of rooms or room and corridor modules can
be used to create varieties of apartment types. These types can be
put together to make interesting and varied buildings of many
forms. The nature of high-rise buildings is such that the modules
are clustered around a core or stabilizing system. The particular
features of the chosen modular system have to be well understood
by the design team at an early stage so that the detailed design con-
forms to the limits of the particular system.
1SCI Professor of Construction Systems, Univ. of Surrey, Faculty
of Engineering and Physical Sciences, Guildford, UK, GU2 7XH (corre-
sponding author). E-mail: m.lawson@surrey.ac.uk
2Professor of Architectural Technology, Oxford Brookes Univ., Oxford,
UK.
3Head of Sustainability, HTA Architects, London, UK.
Note. This manuscript was submitted on December 7, 2010; approved
on July 19, 2011; published online on July 21, 2011. Discussion period
open until November 1, 2012; separate discussions must be submitted
for individual papers. This paper is part of the Journal of Architectural
Engineering, Vol. 18, No. 2, June 1, 2012. ©ASCE, ISSN 1076-0431/
2012/2-148–154/$25.00.
148 / JOURNAL OF ARCHITECTURAL ENGINEERING © ASCE / JUNE 2012
J. Archit. Eng. 2012.18:148-154.
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http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000057
A typical module is 3.3 m (11 ft) to 3.6 m (14 ft) wide (internal
dimensions) and 6 m (20 ft) to 9 m (30 ft) long. A module is 25 to
35 m2 (270 to 375 ft2) in floor area and is often used for single-
person accommodation. Two modules are generally suitable for a
2-person apartment (with one bedroom) and three or four modules
are suitable for family-sized apartments (Lifetime Homes 2010).
In all cases, the kitchens and bathrooms are arranged next to the
corridor or other accessible space so that service connections and
maintenance can be carried out relatively easily.
For modules with load-bearing walls, the side walls of the mod-
ules should align vertically through the building, although openings
of up to 2.5 m width can be created, depending on the loading. For
modules with corner posts, the walls are non-load-bearing, but the
corner posts must align and be connected throughout the building
height. Additional intermediate posts may be required in long mod-
ules, so that the edge beams are not excessively deep.
The design of high-rise modular buildings is strongly influenced
by structural, fire, and services requirements. From a building
layout viewpoint, two generic floor plans may be considered for
the spatial relationship of the modules around a stablizing concrete
core:
• A cluster of modules, which are accessed from the core or from
lobbies next to the core, as illustrated in Fig. 2.
• A corridor arrangement of modules, in which the modules are
accessed from corridors either side of the core, as illustrated
in Fig. 3.
The addition of external balcony systems can be used to create a
layer of external features that provide private space and architec-
tural interest. Balconies can be attached at the corner posts of the
modules or can be ground supported. Integral balconies within
the modules may be provided by bringing the end wall in-board
of the module.
The optimum use of modular construction can achieved by
designing the highly serviced and hence more expensive parts
of the building in modular form and the more open-plan space
as part of a regular structural frame in steel or concrete. This re-
quires careful consideration of the architecture and spatial planning
of the building.
Structural Action of Tall Modular Buildings
The structural behavior of an assembly of modules is complex be-
cause of the influence of the tolerances in the installation pro-
cedure, the multiple inter connections between the modules, and
the way in which forces are transferred to the stabilizing elements,
such as vertical bracing or core walls. The key factors to be taken
into account in the design of high-rise modular buildings are:
• The influence of installation eccentricities and manufacturing
tolerances on the additional forces and moments in the walls
of the modules (Lawson and Richards 2010).
• Second-order effects due to sway stability of the group of mod-
ules, especially in the design of the corner columns of the
modules.
• Mechanism of force transfer of horizontal loads to the stabiliz-
ing system, which is generally a concrete core.
• Robustness to accidental actions (also known as structural
integrity) for modular systems.
In modular systems with load-bearing walls, axial load is trans-
ferred via direct wall-to-wall bearing, taking into account eccen-
tricities in manufacture and installation of the modules, which
causes additional buildup of moments and accentuates the local
bearing stresses at the base of the wall.
Two layers of plasterboard or similar boards are attached to
the internal face of the wall by screws at not more than
Fig. 1. Light steel module with a perimeter framework (image by
R. M. Lawson)
Fig. 2. Typical layout of rooms clustered around a core
Fig. 3. Typical corridor arrangement of modules
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300 mm spacing. Cement particle board (CPB) or oriented strand
board (OSB) are often attached to the exterior of the walls of the
modules. In production, boards may be fixed by air-driven pins
enhanced by glued joints. These boards restrain the C-sections
against buckling in the in-plane direction of the wall.
The ability of an assembly of modules to resist applied loads in
the event of serious damage to a module at a lower level is depen-
dent on the development of tie forces at the corners of the modules.
The loading at this so-called accidental limit state is generally taken
as the self-weight plus one-third of the imposed load, reflecting the
average loading on all floors in this rare event. To satisfy “robust-
ness” in the event of accidental damage to one of the modules,
the tie forces between the adjacent modules may be established
on the basis of a simplified model in which the module is
suspended from its neighbors. For design purposes, it is recom-
mended (Lawson et al. 2008) that the minimum horizontal force
in any tie between the modules is taken as not less than 30% of
the total load acting on the module and not less than 30 kN (3 tons).
Fire Resistance and Acoustic Insulation
In most European countries, 120-min fire resistance is required for
residential buildings of more than 28 stories in height (10 stories
typically), and in some countries sprinklers are also required. The
fire resistance of modular construction derives from four important
aspects of performance:
• The stability of the light steel walls is a function of the load
applied to the wall and the fire protection of the internal face
of the wall of the module.
• The load capacity of the module floor is influenced by the
thermal-shielding effect of the ceiling of the module beneath.
• The elimination of fire spread by fire barriers placed between
the modules (to prevent the spread of smoke or fire in the cavity
between the modules).
• The limiting of heat transfer through the double-leaf wall and
floor-ceiling construction of the modules.
Generally, the internal face of the walls and ceiling of the mod-
ule are provided with two 15 mm (0.6 in.) plasterboard layers
(at least one layer being fire-resistant plasterboard using vermicu-
lite and glass fiber). Mineral wool is placed between the C-sections
(also required for acoustic purposes). The floor and ceiling in com-
bination and the load-bearing light steel walls generally achieve
120-min fire resistance, depending on the sheathing board used
on the outside of the modules.
The double-layer walls and floor-ceiling of the modules also
provides excellent resistance to airborne and impact sound, particu-
larly when supplemented by external sheathing board. Additional
sound reduction and floor stiffness to minimize vibrations can be
achieved by a thin concrete floor screed either placed on the light
steel floor or as a composite slab spanning between the walls or
edge beams.
Case Study of Modules Stabilized by a Concrete
Core—Paragon, West London
For high-rise buildings, the modules are generally designed to resist
only vertical loads, including the cladding and corridor loads, and
horizontal loads are transferred to the concrete core. In the cluster
arrangement, the modules are connected directly to the core, gen-
erally by attaching ties to cast-in plates in the core. In the corridor
arrangement, horizontal loads are transferred via in-plane bracing
in the corridors and are again connected to the core. It follows that
the distance of the outer module from the core is limited by the
shear force that can be transferred via the corridor or by the travel
distance for fire evacuation purposes.
This concept has been used on one major project called Paragon
in west London, shown in Fig. 4 (Cartz and Crosby 2007). A series
of buildings from 11 to 17 stories were constructed using modules
with loadbearing corner posts. The plan form of the L-shaped
building is shown in Fig. 5. The modules were also manufactured
with integral corridors, in which half of the corridor was included in
each module. The corner columns were therefore in-board of the
ends of the modules and the projection of the floor into the corridor
was achieved by the stiff edge beams of the modules.
The project consisted of a total of 827 modules in the form of
600 en-suite student rooms, 114 en-suite studio rooms, and 44 one-
bedroom and 63 two-bedroom key worker apartments. The
17-story building consists of 413 modules. Modules are 2.8 m
(9 ft) to 4.2 m (13.5 ft) wide, which is the maximum for motorway
transport in the UK. The edge beams use 200 × 90 (8 × 3:5 in)
parallel flange channels (PFC) at floor level and 140 × 70
(5:5 × 2:7 in) PFC at ceiling level to design partially open-sided
modules of up to 6 m (20 ft) span. The one- or two-bedroom apart-
ments were constructed using two or three modules, each with a
35 to 55 m2 (375 to 590 ft2) floor area. The plan form is presented
in Fig. 6, which shows the many variations in room layouts that
were possible using corner-supported modules.
Case Study of Modules on a Podium—Bond Street,
Bristol
Modular construction may be combined with steel or concrete
frames to extend the flexibility in space planning in applications
where the dimensional constraints of modular systems would
otherwise be too restrictive. An adaptation of modular technology
is to design a “podium” or platform structure on which the modules
are placed. In this way, open space can be provided for retail or
commercial use or below-ground car parking. Support beams
should align with the walls of the modules and columns are typi-
cally arranged on a 6 to 8 m grid (20 to 26 ft). A column grid of
Fig. 4. 17-story modular building stabilized by a concrete core (image
by R. M. Lawson)
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7.2 m (24 ft) is optimum for car parking at ground floor or
basement.
Fig. 6 shows a 12-story mixed student residence and commer-
cial building in Bristol in the west of England, in which 6 to 10
stories of modules sit on a 2-story steel framed podium. The
400 bedroom modules are 2.7 m (9 ft) external width, but approx-
imately 100 modules are combined in pairs to form “premium”
studios consisting of two rooms. The kitchen modules are 3.6 m
(12 ft) external width. Stability is provided by four braced steel
cores, into which some modules are placed. The plan form is illus-
trated in Fig. 7. A double corridor is provided so that a cluster of
five rooms forms one compartment. Stability is provided by braced
steel cores and the maximum number of modules placed between
the cores is seven.
The building used a lightweight cladding system consisting of a
“rain screen” in which the self-weight of the cladding is supported
by the modules. The air and weather-tight layers and the majority of
insulation is contained within the module as delivered.
Case Study of High-rise Building in Wolverhampton
A 25-story modular construction project in Wolverhampton in the
midlands of England was studied to obtain data on the construction
process. It has three blocks of 8 to 25 stories and in total consists of
824 modules. The tallest building is Block A, which is shown in
Fig. 8 during construction. The total floor area in these three build-
ings is 20;730 m2 (223;000 ft2), including a podium level. The
floor area of the modules represents 79% of the total floor area.
The average module size was 21 m2 (226 ft2) but the maximum
size was as large as 37 m2 (398 ft2).
The project started on site in July 2008 and was handed over to
the client in August 2009 (a total of 59 weeks). Installation of the
modules started in October 2008 after completion of the podium
slab, and construction of the concrete core to Block A was carried
out in parallel with the module installation on Blocks C and B.
Importantly, the use of offsite technologies meant that the site acti-
vities and storage of materials were much less than in traditional
Fig. 5. Plan form of the building in Fig. 4 showing the location of the corner posts in the modules
Fig. 6. 12-story modular student residence at Bond Street, Bristol
(image by R. M. Lawson)
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construction, which was crucial to the planning of this project.
The tallest building, Block A, has various set-back levels using can-
tilevered modules to reduce its apparent size. Lightweight cladding
was used on all buildings and comprises a mixture of insulated
render and composite panels, which are attached directly to the
external face of the modules. The total area of cladding was
10;440 m2 (112;300 ft2) for the 3 blocks.
Construction Data
The module weights varied from 10,000 to 25,000 kg, depending
on their size, and the module self-weight was approximately
5:7 kN∕m2 (120 pounds∕ft2) floor area. The modules in the first
Block C were installed by mobile crane, whereas the modules
in Blocks A and C were installed by the tower crane that was
supported by the concrete core. The installation period for the
824 modules was 32 weeks and the installation team consisted
of a total of eight people plus two site managers. The average
installation rate was 7 modules per day, although the maximum
achieved was as high as 15 per day. This corresponds to
14.5 man-hours per module.
The overall construction team for the nonmodular components
varied from a further 40 to 110 with three to four site managers,
increasing as the 59-week project progressed. It was estimated that
the reduction in construction period relative to site-intensive
concrete construction was over 50 weeks (or a saving of 45% in
construction period).
It was estimated that the manufacture and in-house management
effort was equivalent to a productivity of 7.5 man-hours per square
meter module floor area (0.7 man-hours per square foot) for a
21 m2 (225 ft2) module floor size. This does not take into account
the design input of the architect and external consultants, which
would probably add about 20% to this total effort.
For modules at the higher levels, approximately 14% of the
module weight was in the steel components and 56% in the con-
crete floor slab. At the lower levels of the highrise block, the steel
weight increased to 19% of the module weight. The steel usage
varied from 67 to 116 kg∕m2 (14 to 24 pounds∕ft2) floor area,
which is higher than the 50 to 60 kg∕m2 (10 to 12 pounds∕ft2)
for medium-rise modular systems.
The estimated breakdown of man-effort with respect to the com-
pleted building was 36% in manufacture, 9% in transport and
installation, and 55% in construction of the rest of the building.
The total effort in manufacturing and constructing the building
was approximately 16 man-hours per square meter (1.5 man−hours
per square foot) completed floor area, which represents an esti-
mated productivity increase of about 80% relative to site-intensive
construction.
Deliveries and Waste
Site deliveries were monitored over the construction period. During
installation of the modules, approximately six major deliveries per
day were made, plus the six to twelve modules delivered on aver-
age. During concreting of the cores, approximately 6 × 8 m3
(280 ft3) concrete wagons were scheduled to be pumped to con-
struct the core at a rate of one story every three days.
Waste was removed from site at a rate of only two skips of
6 m3 (210 ft3) volume per week during the module installation
period and six skips per week in the later stages of construction,
equivalent to approximately, 3,000 kg of general waste, including
off-cuts and packaging. This is equivalent to about 9 kg per m2
(1:8 pounds per ft2) floor area.
Fig. 7. Plan of modular building at Bond Street, Bristol, showing the irregular-shaped core positions
Fig. 8. 25-story modular building in Wolverhampton, England, during
construction (image by R. M. Lawson)
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The manufacturing waste was equivalent to 25 kg∕m2
(5:1 pounds∕ft2) of the module area, of which 43% of this waste
was recycled. For the proportion of module floor area to total area
of 79%, this is equivalent to about 5% of the weight of the overall
construction. This may be compared to an industry average of
10 to 13% wastage of materials, with little waste being recycled.
It follows that modular construction reduces landfill by a factor of
at least 70%.
Summary of Sustainability Benefits of Modular
Construction
Modular construction systems provide several opportunities to
improve the sustainability of the project in terms of the construction
process and the performance of the completed building.
• Construction waste is substantially reduced from 10 to 15%
in a traditional building site to less than 5% in a factory envi-
ronment, which also has greater opportunities for recycling
of waste.
• The number of visits to site by delivery vehicles is reduced by
up to 70%. The bulk of the transport activity is moved to the
factory, where each visit can be used to deliver more material
than is usually delivered to a construction site.
• Noise and disruption are reduced on-site, assisted by the 30 to
50% reduction in the construction period, which means that
neighboring buildings are not affected as much as in traditional
building processes.
• The air-tightness and the thermal performance of the building
fabric can be much higher than is usually achieved on-site
due to the tighter tolerances of joints that can be achieved in
a factory environment.
• The efficient use of lightweight materials and the reduced waste
means that the embodied energy of the construction materials is
also reduced.
• Acoustic insulation is greatly improved by the double-layer
construction.
• Safety on-site and in the factory is greatly improved, and it is
estimated that reportable accidents are reduced by over 80%
relative to site-intensive construction. The modules can be
installed with pre-attached protective barriers or, in some cases,
a protective “cage” is provided as part of the lifting system.
Economic Benefits of Modular Construction
Modular construction takes most of the production away from the
construction site, and essentially the slow, unproductive site activ-
ities are replaced by more efficient, faster factory processes. How-
ever, the infrastructure for factory production requires greater
investment in fixed manufacturing facilities and repeatability of
output to achieve economy of scale in production.
An economic model for modular construction must take into
account the following factors:
• Investment costs in the production facility.
• Efficiency gains in manufacture and in materials use.
• Production volume (economy of scale).
• Proportion of on-site construction (in relation to the total
build cost).
• Transport and installation costs.
• Benefits in speed of installation and reduced minor repair costs.
• Savings in site infrastructure and management (preliminaries).
Materials use and wastage are reduced and productivity is
increased, but conversely, the fixed costs of the manufacturing
facility can be as high a proportion as 20% of the total build cost.
Even in a highly modular project, a significant proportion of
additional work is done on-site. Background data may be taken
from a recent National Audit Office (NAO) report “Using Modern
Methods of Construction to Build Homes More Quickly and Effi-
ciently” (National Audit Office 2004). This report estimates that
this proportion is approximately 30% in cost terms for a fully
modular building, and may be broken down approximately into
foundations (4%), services (7%), cladding (13%), and finishing
(6%). However, in many modular projects, the proportion of on-site
work can be as high as 55% (see case study). Modular construction
also saves on commissioning and minor repair costs that can be as
high as 2% in traditional construction.
The financial benefits of speed of installation may be considered
to be:
• Reduced interest charges by the client.
• Early “start-up” of business or rental income.
• Reduced disruption to the locality or existing business.
Thesebusiness-related benefits are clearly affectedby the size and
type of the business. The tangible benefits due to reduced interest
charges can be 2 to 3% over the shorter building cycle. The NAO
report estimates that the total financial savings are as high as 5.5%.
Lessons Learned
The case studies show that modular construction can be used for
residential buildings up to 25 stories high, provided the stability
under wind action is achieved by a concrete or steel framed core.
Modules in tall buildings can be clustered around a core, or alter-
natively, they can be connected to a braced corridor, which transfers
wind-loading to the core. The design of the load-bearing walls or
corner posts should take into account the effects of eccentricities
due to manufacturing and installation tolerances.
Three case studies of modular buildings showed the different
plan forms that can be created depending on the type of modular
system. Modules with corner posts provide more flexibility in
room layouts but are more costly to manufacture than the wholly
light steel load-bearing systems. For the 25-story modular building,
the steel usage ranged from 67 to 117 kg∕m2 (14 to 24 pounds∕ft2)
floor area because the modular system had a concrete floor slab.
The modular components accounted for approximately 45% of
the completed cost of the building. The construction period was
reduced by over 50% relative to site-intensive building. Waste
was reduced by 70% on-site and most manufacturing waste was
recycled.
Conclusions
This paper shows that modular construction can be used for resi-
dential buildings up to 25 stories high, provided the stability is
achieved by a concrete or steel framed core. The structural design
of the modules is strongly influenced by installation and manufac-
turing tolerances and tying action between the modules. In terms of
layout of the modules, three modules efficiently form a two-
bedroom apartment. Modules in tall buildings can be clustered
around a core, or alternatively, they can be connected to a braced
corridor, which transfers wind-loading to the core,
Three case studies are presented of modular buildings of 12, 17,
and 25 stories in height. In the tallest building, data was collected of
themanufacturing and construction operation. For a high-risemodu-
lar building, the steel usage ranged from 67 to 117 kg∕m2 (14 to
24 pounds∕ft2) floor area depending on the floor level. Themodular
components accounted for approximately 45%of the completed cost
of the building. The construction period was reduced by over 50%
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relative to site-intensive building. Waste was reduced by 70%
on-site and most manufacturing waste was recycled.
Acknowledgments
The information in this paper was provided with the assistance of
Caledonian Building Systems, Unite Modular Solutions, Vision
Modular Systems, HTA Architects and the Steel Construction
Institute, UK.
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U.S.C. 154(b) by 0 days. 5,867.964 A * 2/1999 Perrin ………………….. 52/236.8
* cited bw examiner (21) Appl. No.: 09/749,275 y
(22) Filed: Dec. 27, 2000 Primary Examiner-Carl D. Friedman
ASSistant Examiner Basil Katcheves
(Under 37 CFR 1.47) (74) Attorney, Agent, or Firm Vinson & Elkins, LLP
(51) Int. Cl.” ………………………………………….. E04B 1100 (57) ABSTRACT
(52) U.S. Cl. …………………….. 52/79.7; 52/79.1; 52/79.9;
52/79.12 A method of constructing low cost housing is disclosed in
(58) Field of Search …………………………… 52.79.1, 79.7, which modules are produced in a manufacturing facility and
52/79.9, 79.2, 79.12 are transported to a building site on trailers and lifted into
place with a crane. A few standard modules are produced
(56) References Cited and may be arranged in various configurations to produce a
variety of floor plans.
U.S. PATENT DOCUMENTS
3,564.786 A 2/1971 Baker ………………………. 52/79 18 Claims, 13 Drawing Sheets
U.S. Patent Sep. 30, 2003 Sheet 1 of 13 US 6,625,937 B1
U.S. Patent Sep. 30, 2003 Sheet 4 of 13 US 6,625,937 B1
40
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U.S. Patent Sep. 30, 2003 Sheet 5 of 13 US 6,625,937 B1
FIG. 6
U.S. Patent Sep. 30, 2003 Sheet 6 of 13 US 6,625,937 B1
76
63
70
72 48
O’N,
FIG. 7
U.S. Patent Sep. 30, 2003 Sheet 7 of 13
U.S. Patent Sep. 30, 2003 Sheet 8 of 13
FIG. 10
U.S. Patent Sep. 30, 2003 Sheet 9 of 13
U.S. Patent Sep. 30, 2003 Sheet 11 of 13
U.S. Patent Sep. 30, 2003 Sheet 12 of 13
FIG. 14
U.S. Patent Sep. 30, 2003 Sheet 13 of 13 US 6,625,937 B1
US 6,625,937 B1
1
MODULAR BUILDING AND METHOD OF
CONSTRUCTION
SUMMARY
The invention relates to modular building construction
and to buildings in which a plurality of Standard prefabri
cated modules may be arranged in alternate arrangements to
construct desirable multifamily housing at high Volume and
low cost. In a specific preferred embodiment of the
invention, five types of modules are constructed So that three
of the five may be utilized to produce a one bedroom
apartment and that four of the five may be utilized to
produce a two bedroom apartment. Alternate modules or
other combinations of modules may also be used to con
Struct 3 or more bedroom houses or apartments utilizing the
principles demonstrated by the one and two bedroom apart
ments described as preferred embodiments herein. The mod
ules may be used to construct Single family residences or
more preferably to construct multifamily or even multistory
buildings. For example, the invention described herein may
be applied with great advantage to the construction of a
Subdivision or neighborhood of Single family residences, or
for various types of group residences Such as nursing homes,
geriatric housing, military housing, housing for athletes in
an event or training facility, or any type of dormitory related
to an educational or commercial institution. The methods
and buildings described herein are particularly useful as
housing units for urban, low cost multifamily housing and/or
Student housing near colleges or universities, or in any
Setting where a large number of units may be constructed
near a manufacturing facility. Although the preferred
embodiments described herein are residential buildings, the
invention may also encompass commercial buildings that
include offices, Studios, retail spaceS or any combination
thereof.
In a preferred embodiment, a multifamily residential
building includes two building Segments in a face to face
orientation. Each Segment includes a ground floor or first
floor comprising a row of apartments disposed with common
Side walls Separating each apartment from its immediate
neighbor. The apartments may be any combination of one,
two and three bedroom apartments, and a preferred arrange
ment is a row of alternating one and two bedroom
apartments, preferably with 2 of each per floor for a total of
4 apartments per floor. The apartment modules may also be
Stacked vertically to achieve a multistory building of 2, 3, 4
or even 5 floors in a residential building. For use as a low
cost, high Volume production multifamily housing project,
the preferred arrangement is a 3 story building with 12
apartments per building Segment. In a multistory building,
like modules are preferably Stacked on top of like modules
in order to facilitate Vertical utility and electrical connec
tions between floors. For example, a Single utility chase may
be incorporated into the same type of modular unit in each
apartment and these chases would then be aligned vertically
in the multistory building for ease of making vertical con
nections between floors. For multifamily housing
developments, the buildings may be arranged or Spaced in
any manner to facilitate construction and to conform to the
terrain of the building site. In certain building projects, two
building Segments are spaced apart by only a few feet So that
the buildings may share common Stairways, breezewayS,
Sidewalks, or other exterior features, although various other
arrangements are possible. For example, a Stairway may
Serve one apartment per floor in which the apartment
entrances are Substantially vertically aligned, or common
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breezeways may be constructed in the front or rear of the
buildings or both, or Stairways may be constructed in any
combination. In a preferred site development, pairs of build
ing Segments are spaced in opposing fashion to form a
building and share a common breezeway on each floor and
a Stair tower at each end of the buildings Serving each floor.
BRIEF DESCRIPTION OF THE DRAWINGS
The following drawings form part of the present Specifi
cation and are included to further demonstrate certain
aspects of the present invention. The invention may be better
understood by reference to one or more of these drawings in
combination with the detailed description of Specific
embodiments presented herein. It is understood that the
drawings are not necessarily to Scale, but are representations
of the embodiments shown.
FIG. 1 is a floor plan view of a one bedroom unit
constructed from 3 modules.
FIG. 2 is a floor plan view of a two bedroom unit
constructed from 4 modules.
FIG. 3A is a front elevation view of a 12 apartment
building Segment.
FIG. 3B is a side elevation view of the building segment
shown in FIG. 3A in which the opposing Segment can also
be seen.
FIG. 4 is a schematic view of a floor frame for a module.
FIG. 5 is a schematic view of a floor frame for a module
with a bay window.
FIG. 6 is a schematic view of a set of concrete piers with
Structural members Set thereon.
FIG. 7 is a Schematic view of a projection piece used to
connect Vertical members in Vertically Stacked modules.
FIG. 8 is a side view of a roof module prior to installation
of sheathing.
FIGS. 9-15 are a floor plan views of single family
residences constructed of modules as described herein.
DETAILED DESCRIPTION
A preferred embodiment of the present invention is a
building composed of modules that are constructed in a
manufacturing facility, transported to a building site, and are
permanently installed at the building site as adjoining com
ponents of a building. A preferred type of building is a
multifamily residential building that can be constructed in
high Volume at low cost. Constructing modules in a manu
facturing facility Saves labor and material costs because the
materials can be standardized and much of the waste elimi
nated. In addition, most of the proceSS can be automated or
performed by semi-skilled workers. The modules may be
constructed to a Semi-finished State in the manufacturing
facility including the framing of floors, all walls and
ceilings, installation of doors, windows, electrical wiring,
plumbing, wall insulation, ground floor insulation and vapor
barrier, and ducting for heating and air conditioning. The
Semi-finished State may also include exterior sheathing, base
cabinets and plumbing fixtures Such as bathtubs, Sinks or
showers. In a preferred embodiment, the modules are trans
ported to a building site individually on trailers and installed
with a crane at the building Site.
An aspect of the present disclosure is a residential build
ing that is composed of modules and that provides a pleasant
and functional living unit or apartment at a cost that is lower
than would be possible for an apartment that was built on
Site with conventional Site built construction methods com
US 6,625,937 B1
3
mon to the multi-family construction industry. It is also
understood that the building may be easily “up-graded” by
the addition of a higher grade cabinets, floor covering,
appliances, fixtures and other amenities to provide well
constructed more expensive, or even luxury apartments at a
lower cost than is possible with conventional site built
construction.
The preferred embodiment includes one bedroom and two
bedroom apartment units that are constructed using 5 types
of modules. A preferred floor plan design for a one bedroom
apartment is shown in FIG. 1. The one bedroom unit, or
apartment 10, is constructed of 3 modules, a first module 12
providing an entry, living room, and partial laundry room; a
Second module 14 adjoining the first module and providing
a kitchen, dining area, bathroom and the remainder of the
laundry room; and a third module 16 adjoining the Second
module 14 on the opposite side wall from said first module
12 and providing a bedroom and closets. The Second
module, 14 also provides a closet for the heating/air handler
and a utility chase for the water heater and all vertical
plumbing and electrical connections in a multistory build
ing. The Second module in this embodiment also provides a
bay window 11 in the rear wall thereof that is shown in this
drawing to contain a dining room. AS used herein, the term
bay window has its ordinary meaning and is a window Space
that projects outward from the wall of a building. A bay
window may be rectangular, Square or polygonal as shown
in FIG. 1. As can be seen in FIG. 1, the interior side walls
of the modules are abutted to provide double thick walls 18.
A preferred two bedroom apartment is shown in floor plan
view in FIG. 2. The two bedroom apartment 20, utilizes the
same second module 14 and third module 16 as the one
bedroom apartment 10. The apartment 20 also utilizes a
fourth module 22 that is identical to the first module 12
except for a doorway 26 in the Side wall, that provides a
passageway into the Second bedroom module 24. An aspect
of the present disclosure is the use of a few modules in
combination to create functional living space. For example,
the floor plans shown in FIGS. 1 and 2 are designed to
promote a Smooth traffic flow within the living Spaces and
are also designed to accommodate handicapped perSons who
are confined to wheelchairs. Because of this design, the
modular buildings are particularly useful for geriatric com
munities. While the drawings show the preferred apartments
including the proposed furniture, it is understood that the
modules may be furnished differently, or the interior walls
changed without departing from the Spirit of the present
disclosure.
Although the floor plans shown in FIGS. 1 and 2 could be
constructed as Stand alone, Single family dwellings, in a
preferred embodiment of the described building, the build
ing comprises multiple apartments, preferably alternating
one and two bedroom units joined side by Side. Such a
building would include a one bedroom apartment on one end
thereof, abutting a two bedroom apartment, followed by
another one bedroom apartment and then a two bedroom
apartment, and continuing in like manner to the opposite end
of the building. Other arrangements are, of course, possible,
including but not limited to buildings consisting of only one
or only two bedroom apartments, or with a combination of
1, 2 and 3 bedroom apartments, but the described arrange
ment is a preferred embodiment of the invention.
Furthermore, a building comprising two 1 bedroom apart
ments alternating with two 2 bedroom apartments per floor
is particularly preferred.
It is also a preferred embodiment that the multifamily
residential buildings constructed of 2 identical building
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Segments disposed face to face, wherein each is a 3 story
building with 4 apartments per floor, as alternating one and
two bedroom units. In the preferred building, as shown in
FIG. 3A, the modules are placed so that each module is
always Stacked on a like module in Vertical alignment from
floor to floor. In other words, each ground floor module has
only like modules above it up to and including the top floor.
By like modules, is meant a module 12, for example, which
in a 3 story building would only have other modules 12
above it. This arrangement offers certain advantages, as the
bay windows of the dining room modules are in alignment
and the utility chases as shown in module 14 are in Vertical
alignment. When discussing like modules, it is meant that
the modules provide the like portions of an apartment or
living area, and does not necessarily mean the modules are
identical in every way. For example, certain modifications
are made to ground floor modules Such that the construction
of upper modules may differ from that of lower modules. It
is also a preferred embodiment that two building Segments
are constructed in opposing fashion Such that the entries for
each apartment face the opposing building Segment and that
the two building Segments share common breezeways and
Stairways. The preferred arrangement is not a “mirror
image’ arrangement, but rather identical building Segments
that are disposed to face each other.
It is a further aspect of the present invention that each
module includes a Steel frame that forms the perimeter of the
floor and Supports the floor and the ceiling. A Steel frame for
a module is shown in FIG. 4. The floor frame 40, includes
structural steel beams 42 Such as C-channels of about 8
inches in height that form the perimeter of the floor and a
cross beam 44 across the mid line of the module. To support
the floor, light gauge metal floor joistS 46 are connected to
the channels 42, 44 preferably with clip angles. It is also
understood that other materials, Such as dimension lumber,
a composite, a combination of wood and Steel, or a plastic,
fiberglass or injection molded material could be used for the
floor beams and joists, but that the steel described here is the
preferred embodiment. Also shown in FIG. 4 are six vertical
Support columns or stanchions disposed one at each corner,
and one at or near the center of each side wall. Although
there are six columns in the preferred embodiment, other
Structural plans may be used, utilizing either a greater or
fewer number of Support columns as needed for a particular
type of construction. For example, certain modules may
utilize only four columns at the module corners, or as many
as 8 or 12 columns per module as needed. These columns
provide Support for the walls of the module in transferring
horizontal loads, as well as Support for the modules that may
be Stacked above a particular module in use. Also shown in
FIG. 4 is an extension with cantilever beams and joists to
provide an open hallway structure in the finished building.
In the preferred embodiment of an apartment building, the
open hallway Structure forms the floor of a common breeze
way when a building includes two Segments of apartments
disposed in opposition. In that instance, the extension shown
would be welded to a similar extension from the facing
building Segment to provide a form for a plywood Subfloor
with a lightweight concrete filler that would be shared by the
two building Segments. FIG. 5 is a diagram of a floor frame
50 for a module that includes a bay window extension 52 to
provide a bay window as in module 14 shown in FIG. 1 and
2. In the frame formation for the described modular
buildings, all connections are designed giving particular
attention to mass production or factory environment restric
tions.
The described buildings may be placed on any Suitable
type of foundation including, but not limited to concrete
US 6,625,937 B1
S
piers, monolithic Slabs or post-tensioned slabs, driven piles,
or concrete footings, for example. In the described preferred
embodiment, the foundation of the building includes con
crete piers configured to align with and Support each Struc
tural steel column of each ground floor module. The bottom
or ground floor modules may be attached to the foundation
by welding, bolting or any other known method. AS shown
in FIG. 6, the piers 60 are spaced so that the vertical support
members 48 of the ground floor modules are each placed
above a pier when the module is set at the building site. The
piers are capped with a Steel plate, preferably about 34″ in
thickness that is anchored to the pier with 12″ steel studs 64.
Welded to the cap plates are steel projections 66 that extend
into and align the Support members 48 of the ground floor
modules. In a preferred embodiment the projections are
cone-shaped. As shown in FIG. 6, steel plate 62 is preferably
about 10″x10″ and holds a single projection 66. This pier
would be used at an outside edge of the building on a wall
that does not adjoin another unit. At a junction of two
modules as shown in FIG. 6, steel plate 68 is preferably
about 10″x15″ and holds 2 projections 66 spaced to accom
modate Support columns on adjacent modules.
Also shown in FIG. 6 are the perimeter support beams 61
for the ceiling of the lower modules. AS can be seen from the
drawing, the upper end of the Support columns 48 are
substantially hollow, as would be the case with hollow steel
tubes, and a cast metal projection piece 63 is welded or
attached with epoxy into the upper end of each vertical
Support 48. These projections are preferably the same shape
as the projections 66 that are anchored to the pier caps along
with the monolithic bottom extension and aid in alignment
and Support of the modules when placed in the building
during erection and site construction. The projection also
Serves to give mechanical horizontal restraint and to resist
movement in the lateral direction. The top of a vertical
support 48 is shown in FIG. 7. A monolithic piece that
includes the cone shaped projection 63 and a Substantially
Square projection member 72 Separated by a /2″ thick plate
70 is shown welded in the support member 48. The flat plate
70 Serves as a lip or flange to prevent the piece from falling
into the hollow member 48 while the projection 72 extends
into the Support member 48 and aligns the cone shaped
projection 63 when the piece is in place. Also shown in FIG.
7 is a hole 74 in the structural member 48 that accepts a pin
to lock in the lifting devices during lifting of the modules by
a crane during erection.
In the buildings described herein, the roof may be built in
the manufacturing facility and transported to the construc
tion site or they may be built on Site and lifted into place on
the erected buildings. In a preferred embodiment, the roof is
formed from independent modular units Such that each roof
module is designed to provide a roof over a single module.
As shown in FIG. 8 the main supporting elements of the
preferred unit is constructed from light gauge Steel (LGS)
members 82 to form trusses. The light gauge Steel may be
CEE or any other appropriate shape. The trusses are spaced
apart, preferably 4 feet center to center (c/c) and are Sup
ported on spaced steel tubular beams 84. The tubular beams
84 are Spaced to align with the Structural Support columns of
the building and are welded or bonded to the Support
columns in the same manner as Stacked modules are joined.
The trusses are preferably constructed with #10/#12 con
nection Screws at the joints 86 and the connections between
the trusses and the beams is made by welding and/or by
appropriate Screws using light gauge Steel clip angles 88.
The top members of the trusses give Support to the purlins
81, which are preferably light gauge hat Sections or Suitable
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rolled sections spaced at 24″ c/c connected by #10 screws.
The purlins are then covered by decking material 83 such as
%” oriented strand board (OSB) or other type of plywood.
The decking is then covered with shingles.
The System Stability is achieved by connecting the vertical
and bottom members of the trusses by light gauge Steel 18
to 20 gauge hat channel or Similar Suitable rolled Sections
bracing members one of which spans from the top of one
vertical member at the first edge of the roof module to the
bottom member on the opposite edge of the roof module and
a Second Spanning member that connects in the opposite
orientation So that each vertical Support on the edge of the
module is connected to the bottom member on the opposite
edge of the module. The sides of the framed assembly may
then be clad as appropriate with ’72” to %” gypsum board or
other suitable sheathing material. The module is finished by
adding dimensional lumber fascia to the perimeter. The
erection of the roof modules is preferably done at ground
level on preset jigs mounted on a trailer or platform that can
be moved to the building erection Site.
For installation, the roof modules are carried to the
building location on the trailer or other platform and lifted
by crane Slings attached to the base Structural Steel beams
without putting any load on the LGS truss members and
placed directly on the top floor module vertical Supports.
The junction of the roof unit beams and the top floor module
columns are then welded directly or by using /4″ connection
plates. Finally, adjoining roof module members are also
joined by LGS plates at 2 to 3 locations depending on the
height of the members. The roof over the entire building is
completed by lifting Such independent Single roof units and
placing them directly on Support points provided by the top
floor modules below. In the preferred 2 segment building
described herein, the mono-pitch roof units meet at the peak
as shown in FIG. 3B and cover the common breezeway
between the two Segments.
In an alternative embodiment, the collapsible roof mod
ules may be used. These modules are preferably made in
Situations where it is not feasible to construct the rigid roof
described above due to Space limitations and/or height
restrictions during transportation. The overall construction/
erection principles are similar to the rigid roof modules
except that connections between LGS truss members in the
Vertical planes and bottom chord members are formed using
hinges or pins allowing full rotation of the joints. This
enables the truss assembly including final decking and
shingles to rest flat on the bottom members of the trusses that
are welded or otherwise fastened to the main Structural Steel
beams. These units are typically fabricated off site without
the sheathing attached and are placed either on the top of the
floor modules or separately on trailers for transport to the
construction Site. At the building location, the trusses along
with the roof coverings are rotated back to the final position.
Hinges are locked in making them rigid joints. Side sheet
rock or sheathing is then installed and the unit is lifted by
crane for final installation.
The modules as shown and described herein may be made
of any conventional construction materials including gyp
Sum drywall and sheathing and wood Studs. It is a preferred
embodiment, however, that the modules are framed with
Structural Steel and light gauge Steel framing members to
provide further Strength and uniformity of construction.
Certain aspects of the present invention are also methods
of constructing modular buildings. These methods include
producing a plurality of modules in a manufacturing facility,
wherein each module is produced by constructing a Sub
US 6,625,937 B1
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Stantially rectangular Steel frame that defines and Supports
the perimeter of the floor of each module and wherein the
Steel frame is attached to Vertical Structural members, in
certain embodiments, one at each corner of a module and
one at or near the center of each Side wall of a module. In
the disclosed methods, each module is configured to provide
a part of the floor plan of a finished unit; each module is
Substantially rectangular in Shape with a front wall, a rear
wall and two side walls, and each module is configured So
that the side walls of each module extend from the front to
the rear of a building constructed with the modules during
use; the modules are designed to be disposed in parallel
alignment with their Side walls abutting to form a common
wall between modules and with openings in the Side walls of
the modules to provide passageways between modules
within a unit; and the modules may be configured to produce
two or more floor plans for units within a building during
Sc.
The methods further include constructing each module to
a Semi-finished State in the manufacturing facility prior to
transporting the modules to the construction site. The Semi
finished State would include a floor, exterior and interior
walls, windows and a ceiling. The Semi-finished State may
also include sheathing and insulating the exterior walls,
applying drywall and installing Some cabinets, trim,
windows, doors, plumbing and certain plumbing fixtures,
electrical wiring, outlets, fixtures and heating equipment and
ductwork. The interior may also be painted prior to delivery
to the construction site, or it may be painted after erection
and repair of any Superficial defects occurring during trans
portation. The modules may be completed to any Stage in the
interior, but it is preferred to install the electrical fixtures and
flooring at the construction site to prevent damage to hang
ing fixtures during transport and to prevent damage to the
flooring during final construction. After the modules are
completed in the manufacturing facility they are wrapped
with Shrink wrap material for protection from the elements,
loaded individually on flatbed trailers and transported to the
building site. In preferred embodiments, the modules are no
more than 11 or 11% to 14 feet in width to facilitate moving
the modules on public Streets or highways.
The construction process begins in the manufacturing
facility, in which a structural Steel is placed in a jig on a skid
and welded into the floor frame of a particular module type.
The skid is moved through the manufacturing facility as the
module components are added. Light gauge metal floor
joists are added to the floor frame and a subfloor is added to
the floor joists. The Subfloor is preferably a plywood or
oriented strand board (OSB) product that may be covered
with floor covering Such as carpet or vinyl flooring, or it may
be covered with a light weight concrete floor. It is preferred,
however, that carpet or vinyl flooring products are installed
after the module has been placed and most of the construc
tion is complete. The floor frame is constructed Such that
preferably square hollow steel tubes in the floor frame
accept Structural vertical Support columns that extend below
the frame for attachment to either the foundation, if the
module is erected on the ground floor, or to a structural
column of the module below in the building. The vertical
columns are bonded with epoxy and/or welded to the floor
frame assembly. A structural frame is also added to the
Vertical columns at ceiling height, again with the column
extending above the frame to bond to the room module or
roof module above in use. The vertical columns are braced
with Steel cables, with the comer columns braced by diago
nally crossed cables from column to column on the ends of
the modules and interior columns braced from near ceiling
height to the floor structure by steel cables.
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The wall framing is assembled from light gauge Steel
Studs preferably placed in color coded jigs, So that Semi
skilled laborers can produce the correctly framed walls. The
framed wall Sections are placed on a table and sheetrock is
added to the walls and Screwed to the Studs with a carriage
of automated Screw guns. The walls are then attached to the
Structural frame and the modules are constructed to a
Semi-finished State. The modules are then wrapped in Shrink
wrap and transported to a Shipping area, where they are
loaded onto trailers for transportation to the construction
Site.
In the preferred methods, the building site is prepared by
placing concrete foundation piers in the ground for each
ground floor module of a building, wherein each foundation
pier is configured to align with and provide a foundation for
one or two vertical Support members and wherein each pier
is topped with one or two projections configured to extend
into the bottom of a vertical support member when a module
is placed on the piers during construction. When the mod
ules arrive at the building site a lifting gear is attached to
four or more of the vertical structural members and the
module is lifted from the trailer by a crane and placed on the
piers. This proceSS is repeated until the first floor is com
pleted. AS the modules are welded in place, a crew of
workers connects all necessary electrical, plumbing and
ducting connections that run horizontally from module to
module across the ceiling. After the first floor is complete,
Subsequent modules are lifted onto the first floor modules to
construct the Second floor. Again a crew makes the necessary
horizontal connections, joining the modules with %” Steel
plates with double openings and may also run the Vertical
connections into the utility chase of the first floor modules.
After all the modules are set, roof modules are added to the
top floor and the abutting modules are joined with welded
joints thus providing continuity to the final Structure of the
building to ensure Stability. The external connections are
then made to the buildings and the buildings are finished by
conventional means.
While the structures and methods of this invention have
been described in terms of preferred embodiments, it will be
apparent to those of Skill in the art that variations may be
applied to the Structures and/or methods and in the Steps or
in the Sequence of Steps of the methods described herein
without departing from the concept, Spirit and Scope of the
invention. All Such variations apparent to those skilled in the
art are deemed to be within the Spirit, Scope and concept of
the invention as defined by the appended claims.
What is claimed is:
1. A method of constructing residential buildings com
prising:
providing a manufacturing facility configured to produce
a plurality of types of building modules wherein each
module is constructed on a skid, and wherein construc
tion of Said module comprises constructing a floor
frame, including floor joists and a Subfloor, and a
ceiling frame, Said floor frame and ceiling frame being
bonded to structural columns to provide a Structural
frame for Said module;
constructing interior and exterior walls of Said module in
jigs, attaching sheathing to Said interior and exterior
walls, and attaching Said walls to Said Structural frame;
and
constructing Said module to a Semi-finished State in Said
manufacturing facility;
transporting Said Semi-finished modules to a construction
Site on trailers,
US 6,625,937 B1
preparing a foundation for Said residential buildings Said
foundation providing structural Support for each of Said
Structural columns,
lifting Said modules from Said trailers with a crane;
attaching Said modules to Said foundation; wherein Said
Structural columns comprise hollow Steel tubes, and
wherein Said foundation comprises cone shaped pro
jections configured to insert into Said hollow Steel tubes
when Said modules are set on Said foundation, and
wherein attaching Said module to Said foundation com
prises welding Said projections into Said tubes, and
connecting utilities to Said modules and constructing
modules to a finished State;
wherein a plurality of modules are arranged to provide a
residence,
and further wherein at least a portion of Said types of
modules may be configured with alternate adjoining
modules to produce a plurality of floor plans.
2. The method of claim 1, wherein said module comprises
Six Structural columns, one at each corner of Said module
and one near the center of each Side wall of Said module.
3. The method of claim 1, wherein said floor frame,
ceiling frame and Said columns comprise Structural Steel.
4. The method of claim 1, wherein said interior and
exterior walls comprise Studs made of light gauge Steel,
fiberglass, a composite or an extruded material.
5. The method of claim 1, wherein said interior and
exterior walls comprise Studs made of light gauge Steel.
6. The method of claim 1, wherein said semi-finished state
includes exterior walls insulated and covered with sheathing
and drywall, drywall on the ceiling, wiring for electrical
fixtures, appliances and outlets, installed plumbing and
plumbing fixtures, installed electrical plugs and Switches,
installed cabinets, installed trim, windows, doors, heating
and air exchange unit.
7. The method of claim 1, wherein said residence is a
Single family residence.
8. The method of claim 1, wherein said residence is a
multi-family residence.
9. The method of claim 1, wherein said residence com
prises a multi-story building.
10. The method of claim 1, wherein said foundation
comprises concrete piers, a slab, a concrete footing, or
driven piles.
11. A method of constructing a modular building com
prising:
(a) producing a plurality of modules in a manufacturing
facility, wherein each module is produced by construct
ing a Substantially rectangular Steel frame that defines
and Supports the perimeter of the floor and ceiling of
each module and wherein Said Steel frame is bonded to
Vertical Support columns, and wherein
(i) each module is configured to provide a part of the
floor plan of a finished unit;
(ii) each module is Substantially rectangular in shape
with a front wall, a rear wall and two Side walls, and
each module is configured So that the Side walls of
each module extend from the front to the rear of a
building constructed with the modules during use;
(iii) the modules are designed to be disposed in parallel
alignment with their Side walls abutting to form a
common wall between modules and with openings in
the Side walls of the modules to provide passageways
between modules within a unit; and
(iv) the modules may be configured to produce two or
more floor plans for units within a building during
uSe,
15
25
35
40
45
50
55
60
65
10
(b) constructing each module to a semi-finished State in
the manufacturing facility, comprising adding to each
module a floor, exterior and interior walls and a ceiling,
(c) preparing a building site by placing concrete founda
tion piers in the ground for each ground floor module
of a building wherein each foundation pier is config
ured to align with and provide a foundation for one or
two vertical Support members and wherein each pier is
topped with one or two projections configured to
extend into the bottom of a vertical Support member
when a module is placed on Said piers during use;
wherein Said vertical Support members comprise hol
low Steel tubes, and wherein Said foundation comprises
cone shaped projections configured to insert into Said
hollow Steel tubes when Said modules are set on Said
foundation, and wherein attaching Said module to Said
foundation comprises welding Said projections into
Said tubes,
(d) transporting individual modules to said building site
and placing Said modules on Said concrete piers, and
(e) attaching abutting modules with welded joints to
construct one or more complete units in Said building.
12. The method of claim 11, wherein said modules are no
more than 14 feet in width.
13. The method of claim 11, wherein said modules are no
more than 12 feet in width.
14. The method of claim 11, wherein each of said modules
is transported to the building site on a trailer.
15. The method of claim 11, wherein placing the modules
comprises attaching a lifting gear to four or more of Said
Vertical Support members and lifting Said modules into place
with a crane.
16. The method of claim 11, wherein said semi-finished
State includes exterior walls insulated and covered with
sheathing and drywall, drywall on the ceiling, wiring for
electrical fixtures, appliances and outlets, installed plumbing
and plumbing fixtures, installed electrical plugs and
Switches, installed trim, windows, doors, and heating and air
eXchange unit.
17. The method of claim 11, wherein said plurality of
modules comprises:
a first module containing an entry, living room, and
laundry room;
a Second module containing a kitchen, dining area, and
bathroom;
a third module containing a bedroom;
a fourth module containing a bedroom and bathroom; and
a fifth module containing an entry, living room and
laundry room;
wherein Said first, Second and third modules are configured
Such that:
each module comprises a front wall, a rear wall and two
Side walls,
the Second module may be placed with one Sidewall
thereof abutted to a side wall of the first module and the
opposite Side wall of the Second module abutted a Side
wall of the third module to provide a one bedroom
apartment; and
wherein the fifth module may replace the first module of
the one bedroom apartment and a fourth module placed
with a side wall abutted to the side wall of the fifth
module to provide a two bedroom apartment.
18. The method of claim 17, wherein said second module
includes a bay window in the rear wall thereof.
k k k k k
Proceedings of the Institution of
Civil Engineers
Structures and Buildings 163
June 2010 Issue SB3
Pages 151–164
doi: 10.1680/stbu.2010.163.3.15
1
Paper 800013
Received 24/01/2008
Accepted: 07/09/2009
Keywords: failures/stress analysis/
structural frameworks
Robert Mark Lawso
n
SCI Professor of
Construction Systems,
University of Surrey,
Guildford, UK
Jane Richards
Technical Director, WS
P
Cantor Seinuk, London, UK
Modular design for high-rise buildings
R. M. Lawson BSc (Eng), PhD, CEng, MICE, MIStructE, MASCE, ACGI and J. Richards BSc, CEng, MICE
Modular construction is widely used for residential
buildings of four to eight storeys and there is pressur
e
to extend this relatively new form of construction to 1
2
storeys or more. This paper reviews recent modular
technologies, and also presents load tests and the
analysis of light steel modular walls in compression. A
design method for high-rise modular applications is
presented taking account of second-order effects an
d
installation tolerances. For the modular walls tested, it
was found that the plasterboard and external sheathing
boards effectively prevent minor axis buckling of the
C sections, so that failure occurred either by major axis
buckling or local crushing of the section. In all cases, the
results of the tests on 75 mm and 100 mm deep 3
1.6 mm thick C sections exceeded the design resistance
to BS 5950-5 by 10 to 40%. However, an eccentricity of
20 mm in load application reduced the failure load by 18
to 36% owing to local crushing of the C section. Tension
tests on typical connections between the modules and
corridors gave a failure load of 40 kN, which is adequate
to transfer wind forces to a braced core and also to
provide tying action in the event of loss of support to
one corner of a module. Corner posts provide enhanced
compression resistance but their buckling resistance is
dependent on the sway stiffness of the wall panel. It is
also shown that the notional horizontal force
approac
h
for steel structures presented in BS 5950-1 should be
increased for modular construction.
Modular construction comprises prefabricated room-sized
volumetric units that are normally fully fitted out in
manufacture and are installed on site as load-bearing ‘building
blocks’. Their primary advantages are
(a) economy of scale in manufacturing of multiple repeated
units
(b) speed of installation on site
(c) improved quality and accuracy in manufacture.
Potentially, modular buildings can also be dismantled and
reused, thereby effectively maintaining their asset value. The
current range of applications of modular construction is in
cellular-type buildings, such as hotels, student residences,
Ministry of Defence (MoD) accommodation and social housing,
where the module size is compatible with manufacturing and
transportation requirements. The current application of
modular construction of all types is reviewed in a recent Steel
Construction Institute Publication 348 (Lawson, 2007). A paper
in The Structural Engineer (Lawson et al., 2005) describes the
mixed use of modules, panels and steel frames to create more
adaptable building forms.
There are two generic forms of modular construction, which
affect their range of application: load-bearing modules in
which loads are transferred through the side walls of the
modules – see Figure 1; and corner-supported modules in
which loads are transferred by way of edge beams to corner
posts – see Figure 2.
In the first case, the compression resistance of the walls
(comprising light steel C sections generally at 300 to 600 mm
spacing) is crucial. Current heights of modular buildings for
this type of construction are typically limited to four to eight
storeys, depending on the particular modular system and the
size and spacing of the C sections used.
In the second case, the compression resistance of the corner
posts is the controlling factor and for this reason, square hollo
w
sections (SHS) are often used owing to their high buckling
resistance. Building heights are limited only by the size of the
SHS that may be used for a given module size (150 3 150 3
12.5 SHS is the maximum sensible size of these posts).
Figure 1. Partially open-sided module with load-bearing walls
(courtesy PCKO Architects)
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 151
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Resistance to horizontal forces, such as wind loads and
robustness to accidental actions, becomes increasingly
important with the scale and height of the building. The
strategies employed to ensure adequate stability of modular
assemblies, as a function of the building height, are
(a) diaphragm action of boards or bracing within the walls of
the modules – suitable for four to six-storey buildings
(b) separate braced structure using hot-rolled steel members
located in the lifts and stair area or in the end gables –
suitable for six to ten storeys
(c) reinforced concrete or steel-plated core – suitable for taller
buildings.
Modules are tied at their corners so that structurally they act
together to transfer wind loads and to provide for alternative
load paths in the event of one module being severely damaged.
This is the scenario presented in Approved document A of the
Building Regulations (HMSO, 2006), which leads to minimum
tying force requirements. A recent paper (Lawson et al., 2008)
reviews the robustness requirements for modular
construction
based on a ‘localisation of damage’ route. Modules or load-
bearing elements are removed individually to assess the ability
of the rest of the assembly to support the applied loads at the
accidental limit state.
For taller buildings, questions of compression resistance and
overall stability require a deeper understanding of the
behaviour of the light steel C sections in load-bearing walls
and of the robust performance of connections between the
modules. A further issue in the design of modular construction
is that of installation and manufacturing tolerances, which
cause eccentricities in the compression load path and also lead
to additional horizontal forces applied to the modules. This is
considered later in the paper in the context of design to BS
5950-1 (BSI, 2000), which is the standard for structural
steelwork in buildings.
2. HIGH-RISE BUILDING FORMS USING MODULAR
CONSTRUCTION
Modular construction is conventionally used for cellular
buildings up to eight storeys high where the walls are load-
bearing and resist shear forces owing to wind. However, there
is pressure to extend this technology to high-rise buildings by
using additional concrete cores or structural frames to provide
stability and robustness.
One technique is to cluster modules around a core without a
separate structure in which the modules are designed to resist
compression and the core provides overall stability. This
concept has been used on a major project called Paragon in
west London, shown in Figure 3, in which the modules were
constructed with load-bearing corner posts (a paper on this
project was presented in The Structural Engineer (Cartz and
Crosby, 2007).
The building form may be elongated laterally provided that
wind loads can be transferred to the core. This can be achieved
by using in-plane trusses placed within the corridors, or by
consideration of the structural interaction between the modules
and their attachment to the core. Various alternative high-rise
building forms in which modules are clustered around a core
are presented in Figure 4.
An adaptation of this technology is to design a ‘podium’ or
platform structure on which the modules are placed. In this
way, more open space can be provided for retail or commercial
use or below-ground car parking. Support beams should align
with the walls of the modules and columns are typically
arranged on a 6 to 8 m grid (7.2 m is optimum for car parking),
as shown in Figure 5.
For the modular system covered by the tests reported in this
Figure 2. Open-sided module with corner and intermediate
posts supported by a structural frame (courtesy Yorkon and
Joule Engineers)
Figure 3. Modular building stabilised by a concrete core
(courtesy Caledonian Building Systems)
152 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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paper, three building projects have been completed to date
based on the enhanced modular technology. Bond Street,
Bristol is a 12-storey student residence and commercial
building in which six to ten storeys of modules sit on a two-
storey steel-framed podium (see Figure 6). The 400 bedroom
modules are 2.7 m external width, but approximately
100 modules are combined in pairs to form ‘premium’ studios
consisting of two rooms. The kitchen modules are 3.
6 m
external width. Stability is provided by four braced steel cores,
into which some modules are placed (Figure 7).
A second building, Pitwines in Poole, is an eight-storey student
residence comprising approximately 300 modules. Both
buildings use lightweight cladding attached to the walls of the
modules and comprise terracotta tiles or insulated render
cladding. The nature of the student residential sector is that the
construction period is often less than 12 months, and the
installation of modules is generally carried out in the January
to March period for a September completion. A further project
using this technology has been completed in east London and
another is under way in north London. This last project is
shown under construction in Figure 8.
Another modular manufacturer has developed a system using
1B
2P
2B4P
2B4P
2B4P
1B2P
2B4P
9
9
0
0
9
9
0
0
330033006000 6000 12001200
1
2
0
0
2B4P 2B4P
1B2P 1B2P
3B6P
1B2P 1B2P
9
9
0
0
24001200 120060006000
6
6
0
0
6
6
0
0
(a)
(b)
Figure 4. Typical high-rise building forms using modules and
concrete cores (courtesy HTA Architects) (2B4P means a
two-bedroom, four-person apartment for example): (a)
option 1A; (b) option 2
B
2·8 m Modules
Core for
stairs/lifts
300 mm
3–
3·6 m
300 mm
4·5
m
Spa
n of
12–
18 m
6 m
Figure 5. Modules supported by cellular beams acting as a
podium
Figure 6. Twelve-storey modular student residence at Bond
Street, Bristol (courtesy Unite Modular Solutions)
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 153
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SHS corner posts and a concrete floor with perimeter parallel
flange channel (PFC) steel sections. This has been used in eight
to eleven residential buildings, such as the one shown in Figure
9, and construction of taller buildings is in progress. In this
form of heavier modular construction, the effect of
construction tolerances on the forces acting on the corner posts
is much more important –see section 6.4.
3. DESIGN OF
MODULAR WALLS TO
BS 5950-5
Light steel walls and floors in
modular construction are
currently designed to
BS 5950-5 (BSI, 1998), but
interpretation of this standard
is required to take account of
the practical aspects of the
constructional system. In
modular systems with load-
bearing walls, the light steel
C sections in the walls are
subject to potentially
complex loading and
restraint conditions. In most cases, these conditions are as
outlined
below.
(a) Axial load is transferred by way of direct wall–wall
bearing, taking into account eccentricities in manufacture
and installation of the modules, which causes additional
build-up of moments and accentuates the local bearing
stresses at the base
of the wall.
(b) Loading from the floors and ceilings is taken as applied at
the face of the wall (at an eccentricity of half the wall
width), which causes additional local moments.
(c) Restraint is provided at the floor and ceiling positions so
that the effective height of the wall may be taken as its
clear internal height.
(d) Two layers of plasterboard or similar boards are attached to
the internal face of the wall by screws at not more than
300 mm spacing and provide up to 90 min fire resistance.
(e) Cement particle board (CPB) or oriented strand board (OSB)
are often attached to the exterior of the wall for weather-
tightness of the module and to provide some diaphragm
action. In production, boards may be fixed air-driven pins
enhanced by glued joints.
( f ) In taller modular buildings, second-order (P�˜) effects
may occur owing to sway and other eccentricities that are
often neglected in the design of low-rise buildings
The effects of axial loading and eccentricity can be taken into
account in the design of compression members to BS 5950-5
(BSI, 1998), but the stabilising effect of the boards on local and
overall buckling is largely unquantified. It is reasonable to
assume that boards fixed on both sides provide restraint in the
minor axis direction of the C section, but the stiffening effect
of the boards in the major axis (out-of-plane) direction is not
known, nor is the stabilising effect of boards attached only on
one side. This is the subject of the test programme described
below.
The following tests were carried out to verify the structural
action of the load-bearing walls in a typical modular system.
Two series of tests were carried out: one series on 75 mm
deep 3 45 mm wide 3 1.6 mm thick C sections at the Building
Research Establishment (BRE) and one series on 100 mm
deep 3 42 mm wide 3 1.6 mm thick C sections at the
University of Surrey.
Core
2
Core
4
Core
3
Core
1
Corridor
Corridor
Corr
idor
Separating wall
Premier room
modules
Separating wall
Standard
modules
Figure 7. Plan of modular building at Bond Street, Bristol showing the core positions
Figure 8. Eleven-storey modular student residence in north
London under construction (courtesy Unite Modular
Solutions)
Figure 9. Modular residential building, Wolverhampton
(courtesy Vision Modular Structures)
154 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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The tests were intended to establish the compression resistance
of the C sections, nominally placed at 300 mm spacing, taking
account of the restraining and stiffening effects of various
types of board. The sensitivity to eccentricities up to 20 mm
was also investigated, as this exceeds the maximum that may
be envisaged with good control on installation of modules in
practice.
The panels were loaded using a spreader beam and lateral
restraints in the form of PFC sections, and the test arrangement
is illustrated in Figure 10. The eccentricity in load application
was introduced by a 6 mm thick steel plate inserted at the base
of the wall.
The main variables were the type of boards that are attached
on one or both sides and the eccentricity in axial load.
Additional tests were included on taller walls to examine the
influence of slenderness. The boards were fixed using 2 mm
diameter air-driven nails at 200 mm centres, as used in
production of the wall panels. The boards were attached 2 mm
short of the web of the top and bottom track so that the boards
were not loaded directly.
OSB was attached externally and, in some tests, CPB was
included to assess the difference in restraint provided by the
two types of board. Two layers of 15 mm fire-resistant
plasterboard were used internally, as required for 90 min fire
resistance. In two of the tests,
this plasterboard was omitted.
The walls were first loaded up
to around 100 kN to represent
serviceability loading before
loading incrementally to
failure. Deflections were
recorded at the top of the wall
(vertically and horizontally)
and at mid-height
(horizontally). The test failure
loads are presented in Table 1.
The failure load generally
occurred at a relatively small
vertical displacement of less
than 5 mm.
A further series of tests was
carried out on 2300 mm
high 3 600 mm wide wall
panels, comprising three
100 mm deep C sections
with a mid-height noggin
built into the wall panel to
provide lateral restraint in
the minor axis.
Side B
Roller
Spreader
150 75 18
PFC
� �
150 75 18
PFC
� �
2450 mm
11 mm OSB 2 15 mm plasterboard�
75 1·6 C�
Lateral
restraint
Jack
Side A
Plate
150 75 18 PFC� �
1200 mm
150 75 18 PFC� �
(6 mm thick)
Plate
Figure 10. Test arrangement for BRE wall compression tests
Wall test details Wall height: m Eccentricity of
loading: mm
Failure load per C
section: kN
Design resistance to BS
5950-5: kN
Model
factor
75 3 45 3 1.6C:
OSB boards on one side only
2.45 0 64 48 1.33
75 3 45 3 1.6C:
Plasterboard on one side,
2.45 0 97 76 (inc. effect of boards) 1.27
OSB on the other 2.77 0 90 56 (inc. effect of boards) 1.61
2.45 10 79 56 (inc. effect of boards) 1.41
2.45 20 62 47 (crushing) 1.31
75 3 45 3 1.6C:
Plasterboard on one side, CPB
2.45 0 96 76 (inc. effect of boards) 1.26
on the other 2.45 20 52 47 (crushing) 1.10
100 3 42 3 1.6C:
Plasterboard on one side only
2.30 0 57 51 1.13
100 3 42 3 1.6C:
CPB on one side only
2.30 0 70 61 1.14
Model factor ¼ Failure load/design resistance
Table 1. Failure loads of C section wall studs and comparison with BS 5950-5
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 155
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Two additional bending tests were carried out on wall panels
using 75 3 1.6 C sections subject to a line load at mid-span.
The purpose was to calculate the effective stiffness of the wall
panels in order to calculate the modified slenderness of the
C section for the compression resistance to major axis buckling.
The cases considered were
(a) OSB board on one side and two layers of plasterboard on
the other (OSB in compression)
(b) OSB board on one side with no plasterboard on the other
(OSB in compression).
The measured values of Ieff taking into account the stiffening
effects of composite action with the boards were
432 3 103 mm4 and 270 3 103 mm4 per C section respectively.
The calculated second moment of area of the bare C section
was 265 3 103 mm4. It follows that the effective inertia is
increased by 62% for boards fixed on both sides but by only
2% for OSB board on one side.
The light steel walls were analysed in accordance with
BS 5950-5 using measured section dimensions and steel
strengths. Composite action occurred owing to the additional
stiffness of the boards attached to both sides, which increase
the buckling resistance of the wall. The section properties of
the C sections were calculated for the case where the edge lips
are considered to be fully effective.
The strip steel was S350 grade supplied to BS EN 10327 (BSI,
2004b) and measured strengths were in the range 380–405
N/mm2. Calculated compression resistances to BS 5950-5 are
presented in Table 1. The model factor is the ratio of the test
failure load to the compression resistance to BS 5950-5, based
on measured material strengths and geometry.
The attachment of boards to both sides of the wall effectively
prevents minor axis buckling, even for the narrow wall panels
tested and so failure may occur in one of three modes
(a) crushing of the cross-section locally in compression, as in
Figure 11
(b) buckling of the wall in the major axis direction, as in
Figure 12
(c) delamination of the boards from the wall studs, leading to
loss of composite action.
The stiffening effect of the boards leads to a reduction in
slenderness and increase in buckling resistance. Using the
measured 62% increase in bending stiffness of the wall panel,
the effective slenderness of the bare C section is reduced by
22% owing to attachment of the OSB and plasterboards. For a
2.45 m wall panel, the slenderness in the major axis direction
was 79, and so the effective slenderness becomes
0.78 3 79 ¼ 62. This leads to a buckling strength of
pc ¼ 263 N/mm2 according to Table 10 of BS 5950-5 when
using a Q factor (effective area/gross area) of 0.88.
The calculated compression resistance was 67 kN, which is
approximately 70% of the test result of 97 kN. This suggests
that the buckling curve for cold-formed sections used in
BS 5950-5 is conservative. In addition, local buckling of the
Figure 11. Local crushing of C section in compression tests
Figure 12. Wall failure by overall buckling in pure compression
156 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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flanges of C section may be reduced by the attachment of the
boards, which increases the effectiveness of the cross-section.
The eccentricity of load application using a plate below the
wall accentuates local crushing, as well as overall buckling.
The crushing resistance of the C section without consideration
of buckling is calculated from Aeff py. The reduced crushing
resistance owing to eccentric loading may be taken into
account by considering a reduced compression area, Aeff .
Because the buckling resistance is approximately 70% of the
crushing resistance, it follows that buckling will occur first
unless the crushing resistance is reduced by over 30%.
A 10 mm eccentricity caused a 19% reduction in load capacity
and a 20 mm eccentricity caused a 36% reduction in capacity.
However, in the tests, a 10 mm eccentricity did not reduce the
failure load below the theoretical buckling capacity.
The second series of tests on walls used 100 3 1.6C sections
with boards on one side only. These tests showed that minor
axis buckling is prevented by fixing to plasterboard for 1.6 mm
thick steel, but the increase in compression resistance relative
to BS 5950-5 was less than for the 75 mm deep sections. This is
attributable to the lower transverse bending stiffness of the
web of the deeper C section, which means that the unsupported
flange is only partially restrained.
6. STRUCTURAL ACTION OF GROUPS OF
MODULES
The structural behaviour of an assembly of modules is complex
because of the influence of the tolerances that are implicit in
the installation procedure, the multiple interconnections
between the modules and the way in which forces are
transferred to the stabilising elements such as vertical bracing
or core walls. The key factors to be taken into account in the
design of high-rise modular buildings are
(a) the influence of initial eccentricities and construction
tolerances on the additional forces and moments in the
walls of the modules
(b) application of the design standard for steelwork, BS 5950-1
to modular technology, using the notional horizontal load
approach
(c) second-order effects due to sway stability of the group of
modules, especially in the design of the corner columns
(d) mechanism of force transfer of horizontal loads to the
stabilising system, for example concrete cores
(e) robustness to accidental actions (also known as structural
integrity) for modular systems.
These aspects are now discussed in turn.
6.1. Influence of constructional tolerances
The
National Structural Steelwork Specification for Building
Construction (NSSS) (BCSA, 2007) presents the permitted
tolerances of steel frames, in which the maximum out-of-
verticality of a single column is �H < height/600, but < 5 mm per storey. Furthermore, for steel-framed buildings of more
than ten storeys high, the maximum out of verticality over the
total building height is limited to 50 mm in the NSSS.
BS EN 1090-2 (BSI, 2008) concerns the execution of structures
and in it, the essential tolerances define the maximum
deviations that are permitted so as not to impair the overall
performance of a structure or member. BS EN 1090-2 Table
D.1.12, referring to multi-storey frames, differs from the NSSS
in that the cumulative error over n floors each of height h is
given by h
ffiffiffi
n
p
=300. It follows that the permitted cumulative
deviation over n storeys is 10
ffiffiffi
n
p
mm (for h ¼ 3 m) to BS EN
1090-2.
These permitted deviations for steel frames may not, however,
reflect the practicalities involved in modular construction
because of the difficulties in precisely positioning one module
on another and in making suitable connections. For a single
module placed on another module, it is proposed that the
maximum out of alignment during installation may be taken as
12 mm in orthogonal plan directions relative to the top of the
module below. This alignment requires careful control on site,
especially in windy conditions.
For a vertical stack of modules, the cumulative positional error,
e, owing to installation can be partially corrected over the
building height. Using the same logic as in BS EN 1090-2, the
cumulative positional tolerance (in millimetres) may be taken
statistically as e < 12 ffiffiffi n
p
, where n is the number of modules in
a vertical group. Typically, for n ¼ 10, the total cumulative
positional tolerance that is permitted becomes approximately
40 mm, but this neglects the geometric tolerances in the
module manufacture.
An alternative simplified procedure that is easier to control on
site is to limit the cumulative positional tolerance to 5 mm per
module in orthogonal directions with a maximum of 50 mm
(for n ¼ 10), which is similar to the NSSS. However, it is
considered that the maximum positional error of one module
on another may be taken as 12 mm (except at ground level
where a maximum of 5 mm should be achievable). This means
that at the first floor, the cumulative tolerance of 10 mm will
control, even if the first-floor module is 12 mm out of position
relative to the base module and the base module is positioned
at < �2 mm from datum.
Added to this positional error is the possibility of a systematic
manufacturing error in the geometry of the modules. For a
single module, the maximum permitted tolerance in geometry
may be taken as illustrated in Figure 13. However, over a large
number of modules, the average error in manufacture may be
taken as half of the permitted tolerance for a single
module.
Therefore, the out of verticality of the corner posts may be
taken as h/1000, where h is the module height (typically 3 m).
To take account of manufacturing tolerances, the cumulative
out of verticality over the building height may be taken as
nh/1000, or approximately 3n mm. The total permitted out-
of-verticality �H over the building height, consisting of a
stack of n modules vertically, is therefore a combination of
positional and geometric tolerances, approximately as
follows
�H < e þ nh=1000 ¼ 5n þ 3n ¼ 8n mm1
Using this simplified formula, it follows that �H ¼ 80 mm for
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 157
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n ¼ 10 storeys, which is equivalent to approximately h/350 per
floor. This is 60% higher than the tolerance permitted for
structural steelwork and reflects the different installation and
connection methods between structural frames and a group of
modules.
It is recommended that the absolute out of verticality in
modular construction is limited to a maximum of 80 mm
relative to a ground datum, which will control for buildings of
ten or more storeys. This is achievable with good control on
installation. Adjustments in module position should be made
gradually rather than at a few positions, which would
otherwise add to local eccentricities. These adjustments can be
made by varying the cavity spacing between the modules. In
detailing, the cavity width should be at least equal to half of
the expected maximum tolerance, or as a simple rule, taken as
a minimum of 40 mm.
6.2. Application of notional horizontal forces in modular
construction
A way of assessing the sway stability of a group of modules is
by using the notional horizontal force approach given in clause
2.4.2.3 of BS 5950-1. For steel frames, this horizontal force
corresponds to 0.5% of the factored vertical load acting per
floor, and is used in the absence of wind loading. It represents
the minimum horizontal force that is used to assess the sway
stability of a frame. A further limit for the combination of
wind and vertical load is that the wind load should not be less
than 1% of the factored dead load acting horizontally. This
may control where the self-weight exceeds the imposed loading
on a floor.
BS EN 1993-1-1 Eurocode 3 clause 5.3.2 (BSI, 2004a) permits
an out-of-verticality of L/200 for a single column, but this is
reduced by a factor of 2/3 when considering the average over a
number of storeys (i.e. �H < L/300). The permitted out of verticality of a whole structure is obtained by multiplying this
value for a single column by a factor of f[0:5 [1 þ (1=m)]g0
:5
for m columns in a group horizontally. The result tends to
�H < L/420, which is higher than in the NSSS, but further requirement in the approach of Eurocode 3 is that this out of
verticality is considered in combination with wind loading
rather than as an alternative load case, as in BS 5950-1.
The combined eccentricity on a vertical assembly of modules
takes into account the effects of eccentricities of one module
placed on another, and the reducing compression forces on the
walls acting at the increased eccentricity with height. This effect
is illustrated in Figure 14. The walls of the module are unable to
resist high moments owing to these effects and so the equivalent
horizontal forces required for equilibrium are transferred as
shear forces in the ceiling, floors and end walls of the modules.
The total additional moment acting on the base module is
therefore given by an effective eccentricity ˜eff multiplied by
the compression force in the base module, as follows
� h/500
h Bow /1000� hOut of
verticality
/500� h
Datum position
Idealised dimensions
Actual
dimensions
of module
Width
tolerance
/500� h
Length tolerance /500� h
Figure 13. Permitted maximum geometric errors in
manufacture of modules
P
� �
� �
� �
1
2
1000
e
h
�P
P
P
P
P
P
∆3
∆2
∆1
h
P( 1)/n n�
P( 2)/n n�
P P
e1 M P� e
e3
e2
V
V
1:1000 1:1000
(a) (b)
Figure 14. Combined eccentricities acting on the ground-floor modules: (a) shear in end walls due to eccentric loading for a
four-sided module; (b) transfer of eccentric loading to stabilising system for corner-supported modules
158 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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Madd ¼ Pwall˜eff
¼ Pwall
(n � 1)
n
þ 2
(n � 2)
n
þ 3
(n � 3)
n
. . . þ
1
n
� �
3 (e þ h=1000)
2
where Pwall is the compression force at the base of the ground-
floor module ¼ nWu, n is the number of modules in a vertical
assembly, e is the average positional eccentricity per module, h
is the module height (in mm), and Wu is the factored load
acting on each module.
As a good approximation, it is found that the following
formula holds for the effective eccentricity of the vertical stack
of modules as a function of n:
˜eff ¼
n � 1
6
� �
8n3
The effective base eccentricities are presented in Table 2 for
n ¼ 6 to 12 storeys and for a module height, h ¼ 3 m. This
eccentricity may be converted to a notional horizontal force
applied at each floor level, which is expressed as a percentage
of the vertical load acting at each floor level, and is defined as
the force which causes the same equivalent moment in the base
module as the effective eccentricity in Equation 2. This
moment is given by
kWun
2 h=2 ¼ Pwall˜eff ¼ nWu˜eff4
where k is the proportion of the factored load acting on each
floor, and so
k ¼
8(n � 1)
3h
� �
or
n � 1
3n
� �
80
h
� �
for n . 105
From Table 2, and using the tolerances defined above, it is
calculated that the notional horizontal force varies from 0.5% to
0.9%, when expressed as a percentage of the vertical load
applied to the module. It should be noted that k ¼ 0.5%, when
the maximum tolerance is 50 mm, which agrees with BS 5950-1.
For modular construction, it is therefore recommended that the
notional horizontal force is taken as a minimum of 1% of the
factored vertical load acting on each module, which reflects the
higher tolerances that are permitted in modular construction. It
is used as the minimum horizontal load in assessing overall
sway stability of the structure, and it is proposed that it is used
in combination with wind forces.
As an example, for a module of 25 m2 floor area subject to
factored loading of 7 kN/m2, the notional horizontal force
acting in orthogonal directions is approximately 2 kN. For a
vertical stack of ten modules, the base shear is therefore 20 kN.
This shear force may be shared between the two walls of the
module in the direction under consideration. The notional force
may be compared with a wind load of up to 10 times this
magnitude acting as a shear on the longitudinal side façade of
the building, and so is still relatively small. The notional
horizontal force may, however, control when there are less
than 10 modules in a horizontal group.
If the modules are unable to resist the horizontal force required
for overall stability, the forces must be combined for a number
of modules on plan at each level and transferred to the
stabilising system. This may be the case for partially open-
sided modules.
6.3. Forces at module interconnections
The structural interactions within a group of modules are
complex. Horizontal forces may be transferred by tension and
compression forces in the ties at the corners of the modules by
utilising the diaphragm action of the base and ceiling of the
modules. Shear forces may be transferred through the
continuous corridor members rather than the corner
connections because of the potential articulation through the
bolts and connecting plates between the modules. These actions
are illustrated in Figure 15.
Where the corridor floor is used to transfer shear forces, the
connection of the modules to the corridor may be made by a
detail of the form of Figure 16. The extended plate is screw
fixed on site to the corridor members and is bolted to the re-
entrant corners between the modules so that it also acts as a tie
plate. This detail is not used to provide vertical support to the
corridor floor, which is supported on continuous angles
attached to corridor wall of the modules.
The forces in the tie connection in Figure 16 may be calculated
on the basis of the wind forces acting on the module. The
highest force occurs for an external pressure coefficient of
+0.85 and a negative internal pressure of �0.3. The wind force
on one module is divided between two module-to-corridor
connections. For a wind pressure of 1.2 kN/m2, the force in this
connection is approximately 8 kN at working loads.
The shear attachment to the core is made both through the
corridor and also at the module adjacent to the core. This
Number of
modules
Approx. building
height: m
Cumulative out-of-verticality
at top of building: mm
Effective eccentricity on base
module – Simplified formula in
Equation 3: mm
Notional horizontal force
Equation 5: %
n ¼ 6 16 48 5/6 3 48 ¼ 40 0.5
n ¼ 8 22 64 7/6 3 64 ¼ 75 0.7
n ¼ 10 27 80 9/6 3 80 ¼ 120 0.9
n ¼ 12 33 80 11/6 3 80 ¼ 147 0.9
Table 2. Summary of effective eccentricities and notional horizontal forces in modular construction as a function of building height
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 159
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connection force at the core is designed for the aggregate of
the module–corridor connection forces, which for a group of
three to four modules is 24 to 32 kN (factored loading ) or 18
to 24 kN as a working load.
6.4. Stability of corner posts in modular construction
Corner posts add to the compressive resistance of a wall and, if
they are included in the module, it is normal practice to
assume that all the applied vertical loads acting on the module
are resisted by the corner posts. These posts are usually in the
form of steel angle sections for low-rise applications, or SHSs
for taller buildings. The posts are effectively restrained from
buckling by the in-plane stiffness of the walls of the modules
to which they are connected, but this assumption may not be
valid for partially open-sided modules or for highly perforated
walls.
Consider the stability of the corner posts of a module when
restrained only by the in-plane stiffness of the walls of the
module, as illustrated in Figure 17. The posts are discontinuous
at the module–module connections and do not contribute to
the sway stiffness of the structure, but are restrained against
buckling in their height between the connection points.
The initial out of verticality of the corner post increases under
an axial load, P, in each post, which may be approximated by
strut buckling theory, according to
� ¼
�o
1 � 2P=Pcritð Þ
6
where P is the axial compression acting on one post; �o is the
initial out of verticality and eccentricity of the corner post; Pcrit
is the critical buckling resistance for sway stability of the
module.
From this simple shear failure mechanism, the work done in
Module
(a)
θ
Tie
L
B
Tie in corridor
(b)
Forces
in ties
Module
Figure 15. Force transfer between modules: (a) force transfer
at corridor – bending action; (b) force transfer at corridor –
pure shear
80
7030 gap
Bolt hole
Upper module
Lower module
(a)
(b)
Figure 16. Connection detail between the corridor cassette
and modules: (a) sketch detail; (b) actual detail
160 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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shear and compression may be equated, in order to determine
the critical buckling load, Pcrit, as follows
k˜2
2
¼
2Pcritð Þ˜2
2h
or Pcrit ¼ 0:5kh7
where k is the shear stiffness of the wall panel.
As P approaches Pcrit, so the shear deflection of the wall panel
increases rapidly. Therefore, it is necessary to keep P well
below Pcrit to avoid instability effects. The eccentricity of load
causes both bending in the post and shear in the wall panel.
The shear stiffness of the wall can be estimated from shear
diaphragm tests and corresponds to the horizontal load at a
serviceability deflection of h/500, where h is the module height
in millimetres. This is achieved for a shear force of typically
(a) 10 kN for a 2.4 m wide wall panel with a window, or
approximately 4 kN/m width
(b) 20 kN for a 2.4 m wide unperforated panel, or
approximately 8 kN/m width.
In the case of a module with h ¼ 3 m and width of b ¼ 3.6 m,
it follows that the typical shear stiffness of an end wall panel
with a window becomes
k ¼
4 3 3:6 3 500
3:0
¼ 2400 kN=m
Inserting this value of k in Equation 7 leads to a critical
buckling load owing to shear in the end wall of a module of
Pcrit ¼ 0:5 3 2400 3 3 ¼ 3600 kN
To check the stability of the corner post, it is recommended
that the eccentricity in load application is taken as the
maximum positional eccentricity of 12 mm when one module
is placed on another plus the maximum out of verticality in
manufacture of a single module (or h/500, as shown in Figure
13). For a 3 m high module, �o ¼ 12 + 6 ¼ 18 mm. These
eccentricities are illustrated in Figure 18.
In addition, a local moment is transferred from the floor or
edge beam, which may act in the same sense as the positional
eccentricity. For a floor–wall junction, this shear load may be
assumed to act at the face of the wall studs (or a minimum of
50 mm). For a corner post, the shear load acts at the centre of
the bolt group, and a minimum eccentricity of 75 mm from the
centre of the post may be used. This local moment acts only on
individual modules and is not cumulative.
The additional moment acting on a corner post is calculated
from M ¼ P�, where � is given by Equation 6. For a wall, the
effective eccentricity also includes the bow in the wall between
the corners (or h/1000, as shown in Figure 14).
For a corner post, the effective eccentricity is therefore given
by �o ¼ 18 + 75/n mm. For a load-bearing wall, the effective
eccentricity is given by �o ¼ 21 + 50/n mm. For n ¼ 10, the
effective eccentricities become approximately 25 mm in both
cases.
The stability of a corner post is then checked as
P=Pc þ M=Mc < 1:08
where P is the load acting at the top of the base module and Pc
is the compression resistance of the post.
When the post is restrained against buckling in its height by
attachment to the adjacent walls, then the bending resistance
may be taken as Mc ¼ Mel, where Mel is the elastic bending
resistance of the post. Elastic properties should be used in order
to take account of uncertainties in this simple linear interaction
method in Equation 8.
For an unsupported post (not restrained by the walls), the
compression resistance is given by Pc ¼ pcA, where pc is
calculated from the minor axis slenderness of the post and Mc
B
P P
H
2P
∆
K
φ
Figure 17. Sway stability of the wall of a module for corner
posts in compression
Pmax
( 1)n �
nPmax
( 1)n �
n
Wall of
module
Floor
Floor
φ 0·002�
� /500h
Ceiling
Mfloor
Pmax Pmax
b
w
h
Mfloor � 0·25 wbd
d
e
Figure 18. Illustration of eccentricity of forces applied to the
walls or corner posts of a module
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 161
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is the bending resistance for lateral torsional buckling. The
interaction equation is also modified to take into account
bending in two directions, as in BS 5950-1.
As an example for a 7.2 m long 3 3.6 m wide module, with a
factored floor load of 7 kN/m2, the compression force acting at
the top corner of the ground-floor module in a 12-storey
building is approximately
P ¼ 7 3 7:2 3 3:6 3 (12 � 1)=4 ¼ 499 kN
Check the compression resistance of the corner posts using
100 3 100 3 10 SHS (in S355 steel), which are stabilised by
the walls of the modules: crushing resistance, Py ¼ 1239 kN,
and bending resistance, Mel ¼ 32.8 kN m.
The out-of-plane displacement and its associated moment, M,
are obtained from Equation 6
�o ¼ 18 þ 75=n ¼ 25 mm
� ¼
25
1 � 2 3 499=3600ð Þ
¼ 34 mm
M ¼ 499 3 0:034 ¼ 17:0 kN m
Using the linear combination of axial force and moment for
member stability
P=Pc þ M=Mel ¼ 499=1239 þ 17:0=32:8
¼ 0:40 þ 0:52 ¼ 0:92 , 1:0
It follows that the effect of eccentricity in installation and out
of verticality in manufacture is to reduce the compressive
resistance of a corner post by about 60%. It is also
recommended that for simple design, the effective eccentricity
of load acting on the corner post is taken as not less than
35 mm, which allows for a 40% magnification in sway from
the initial eccentricity of 25 mm.
6.5. Robustness to accidental damage
The ability of an assembly of modules to resist applied loads in
the event of serious damage to a module at a lower level is
dependent on the development of tie forces at the corners of
the modules. The loading at this so-called accidental limit state
is taken as the self-weight plus one third of the imposed load
all multiplied by a partial factor of safety of 1.05 to BS 5950-1.
To satisfy ‘robustness’ in the event of accidental damage to one
of the modules, the tie forces between the adjacent modules
may be established on the basis of a cantilever model, as
presented in a recent paper (Lawson et al., 2008). Assuming
that the worst case corresponds to loss of support to one side of
a corner module and that each module above is able to develop
tying forces equally, the tension force in the ties is given as
follows
T ¼
Wab
4h
� �
9
where Wa is the load acting on the module at the accidental
limit state, and b and h are the dimensions of narrow end of
the module.
Figure 19 shows the results of a finite-element analysis of a
module when one corner support is removed, which is a more
likely case than complete removal of one side wall. The applied
load is taken as 10 kN/m per wall for a heavyweight module
using the partial factors noted above. Torsional stiffness of the
module is developed by diaphragm action of the walls and
floor/ceiling. From this analysis, the maximum horizontal tying
force is equal to 26% of the total load applied to the module
(rather than 48% in the cantilever formula) and the maximum
vertical load is approximately 40% of the total load. It is
concluded that the minimum values of the horizontal tying
force, T, may be taken as 30 kN for lightweight modules (self-
weight , 3.5 kN/m2) or 50 kN for heavyweight modules (self-
weight , 6 kN/m2).
6.6. Module connection tests
As part of the development programme for the modular
supplier, tests on complete modules were carried out at the BRE
to assess the tensile resistance of the tie detail between the
corridor cassette and the corner of the module. The tie
connection is made at the re-entrant corner of the module.
The module was held in place at two corners and a tensile force
was applied at the top opposite corner causing pull-out of the
connecting bolt to the 4 mm thick corner angle manufactured
as part of the module. Forces within the module are transferred
by way of in-plane diaphragm action of the ceiling and walls.
A rigid corner gusset plate was attached across the junction
between the bottom track and the end wall stud, and the
tension force reached of 40 kN at failure corresponding to a
displacement of 10 mm. The gusset detail at a load level of
25 kN is shown in Figure 20. The load–deflection graph for
this test is shown in Figure 21.
27 kN
5 kN
1 kN
56 kN
27 kN
5 kN
1 kN
38 kN
38 kN
50 kN
38 kN
3·6 m
2·7 m
10 kN/m
10 kN/m
Deflected shape
7·2 m
32 mm
vertically
Figure 19. Illustration of tie forces when support to one
corner of a module is removed
162 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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The test using a stiffening plate at the corner of the module
showed that this arrangement offers the best solution for the
module-to-corridor connection. The characteristic resistance of
this connection is taken as 20% less than the failure load of a
single test, or 0.8 3 40 ¼ 36 kN, which exceeds the calculated
load of 24 kN for transfer of wind forces across three modules
to an adjacent core.
This paper presents the results of tests on light steel walls in
compression, which are used to demonstrate the extension of
modular construction up to 12 storeys high. The tests showed
that the stiffening effect of the fascia boards is very high and
that the compression resistance of the C sections is increased in
comparison to the bare steel section. These conclusions refer to
internal wall heights of 2.3 to 2.8 m using 75 mm to 100 mm
deep C sections.
(a) Minor axis buckling is effectively prevented by attachment
of various types of boards on one side only, provided the
steel thickness is not less than 1.6 mm.
(b) The test load capacities exceeded the design resistance to
BS 5950-5 by 10 to 40% due to the stiffening effects of the
attached boards.
(c) The effective bending stiffness of the bare steel sections is
increased by up to 62% due to the attachment of OSB and
CPB boards on both sides.
(d) The effect of 10 mm out-of-plane eccentricity in load
application reduces the failure load by 19%, and the effect
of 20 mm out-of-plane eccentricity accentuates local
crushing and reduces the failure load by 18 to 36%.
The tests on the module-to-module connections showed that a
tying force of 40 kN can be resisted. For robustness to
accidental actions, the minimum tying force between modules
should be taken as 30 kN for lightweight modules (self-weight
, 3.5 kN/m2) and 50 kN for heavyweight modules.
The effect of installation and geometric inaccuracies must be
taken into account in the design of modular buildings. It is
proposed that the maximum positional error is 12 mm for one
module placed on another. When combined with
manufacturing tolerances, it is proposed that the maximum out
of verticality should not exceed 8 mm per module in a vertical
group (or an absolute maximum of 80 mm) relative to ground
datum. Using these tolerances, the notional horizontal force
used to evaluate stability of a group of modules should be
taken as a minimum of 1% of the applied vertical load on the
modules, which acts in combination with wind loading but at
reduced load factors.
For modules designed with corner posts, it is shown that an
additional effect owing to the shear flexibility of the end walls
has to be taken into account when calculating the moments
acting on the posts due to sway effects. The minimum
eccentricity for design of the corner posts should not be less
than 35 mm taking account of second-order effects, and the
minimum eccentricity for design of load-bearing side walls
should not be less than 25 mm.
The structural testing at the Building Research Establishment
was funded by Unite Modular Systems Ltd as part of their
development strategy. The contribution of Dave Brooke and the
team in the Heavy Structures Lab at BRE is gratefully
acknowledged. Additional wall tests at the University of Surrey
were funded by Metek UK Ltd.
BCSA (British Constructional Steelwork Association) (2007)
National Structural Steelwork Specification for Building
Construction, 5th edn. BCSA, London.
BSI (British Standards Institution) (1998) Structural Use of
Steelwork in Building. Code of Practice for Design of Cold
Formed Thin Gauge Sections. BSI, London, BS 5950: Part 5.
BSI (2000) Structural Use of Steelwork in Building. Code of
Figure 20. Tensile test on module with stiffening plate
�1
0·00
0·00
10·00
20·00
30·00
40·00
50·00
�5 0 5 10 15 20 25 30
Deflection mm
L
o
a
d
:
kN
Figure 21. Load–displacement results for module test with
stiffening plate. Unite module corner test 7
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 163
Downloaded by [] on [14/12/18]. Copyright © ICE Publishing, all rights reserved.
Practice for Design of Simple and Continuous Construction:
Hot Rolled Sections. BSI, London, BS 5950 Part 1.
BSI (2004a) Eurocode 3: Steel Structures – General Rules and
Rules for Buildings. BSI, London, BS EN 1993-1-1.
BSI (2004b) Specification For Continuously Hot-dip Zinc Coated
Structural Steel and Strip – Technical Delivery Conditions.
BSI, London.
BSI (2008) Execution of Steel Structures and Aluminium
Structures. Part 2 Technical Requirements for Execution of
Steel Structures. BSI, London, BS EN 1090-2.
Cartz JP and Crosby M (2007) Building high-rise modular
homes. The Structural Engineer 85(l9): 20–21.
HMSO (2006) England and Wales Approved Document A.
HMSO, London
Lawson RM (2007) Building design using modules. The Steel
Construction Institute, London, Publication 348.
Lawson RM, Ogden RG, Pedreschi R, Popo-Ola S and Grubb J
(2005) Developments in pre-fabricated systems in light steel
and modular construction. The Structural Engineer 83(6):
28–35.
Lawson RM, Byfield M, Popo-Ola S and Grubb J (2008)
Robustness of light steel frames and modular construction.
Proceedings of the Institution of Civil Engineers, Buildings
and Structures 161(1): 3–16.
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164 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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- 1. INTRODUCTION
- 2. HIGH-RISE BUILDING FORMS USING MODULAR CONSTRUCTION
- 3. DESIGN OF MODULAR WALLS TO BS 5950-5
- 6. STRUCTURAL ACTION OF GROUPS OF MODULES
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
4. COMPRESSION TESTS ON MODULAR WALLS
Figure 7
Figure 8
Figure 9
Figure 10
Table 1
5. ANALYSIS OF WALL TESTS TO BS 5950-5
Figure 11
Figure 12
6.1. Influence of constructional tolerances
Equation 1
6.2. Application of notional horizontal forces in modular construction
Figure 13
Figure 14
Equation 2
Equation 3
Equation 4
Equation 5
6.3. Forces at module interconnections
Table 2
6.4. Stability of corner posts in modular construction
Equation 6
Figure 15
Figure 16
Equation 7
Equation 8
Figure 17
Figure 18
6.5. Robustness to accidental damage
Equation 9
6.6. Module connection tests
Figure 19
7. CONCLUSIONS
ACKNOWLEDGEMENTS
Figure 20
Figure 21
REFERENCES
BCSA 2007
BSI 1998
BSI 2000
BSI 2004a
BSI 2004b
BSI 2008
Cartz and Crosby 2007
HMSO 2006
Lawson 2007
Lawson et al. 2005
Lawson et al. 2008
Proceedings of the Institution of
Civil Engineers
Structures and Buildings 163
June 2010 Issue SB3
Pages 151–164
doi: 10.1680/stbu.2010.163.3.15
1
Paper 800013
Received 24/01/2008
Accepted: 07/09/2009
Keywords: failures/stress analysis/
structural frameworks
Robert Mark Lawso
n
SCI Professor of
Construction Systems,
University of Surrey,
Guildford, UK
Jane Richards
Technical Director, WS
P
Cantor Seinuk, London, UK
Modular design for high-rise buildings
R. M. Lawson BSc (Eng), PhD, CEng, MICE, MIStructE, MASCE, ACGI and J. Richards BSc, CEng, MICE
Modular construction is widely used for residential
buildings of four to eight storeys and there is pressur
e
to extend this relatively new form of construction to 1
2
storeys or more. This paper reviews recent modular
technologies, and also presents load tests and the
analysis of light steel modular walls in compression. A
design method for high-rise modular applications is
presented taking account of second-order effects an
d
installation tolerances. For the modular walls tested, it
was found that the plasterboard and external sheathing
boards effectively prevent minor axis buckling of the
C sections, so that failure occurred either by major axis
buckling or local crushing of the section. In all cases, the
results of the tests on 75 mm and 100 mm deep 3
1.6 mm thick C sections exceeded the design resistance
to BS 5950-5 by 10 to 40%. However, an eccentricity of
20 mm in load application reduced the failure load by 18
to 36% owing to local crushing of the C section. Tension
tests on typical connections between the modules and
corridors gave a failure load of 40 kN, which is adequate
to transfer wind forces to a braced core and also to
provide tying action in the event of loss of support to
one corner of a module. Corner posts provide enhanced
compression resistance but their buckling resistance is
dependent on the sway stiffness of the wall panel. It is
also shown that the notional horizontal force
approac
h
for steel structures presented in BS 5950-1 should be
increased for modular construction.
Modular construction comprises prefabricated room-sized
volumetric units that are normally fully fitted out in
manufacture and are installed on site as load-bearing ‘building
blocks’. Their primary advantages are
(a) economy of scale in manufacturing of multiple repeated
units
(b) speed of installation on site
(c) improved quality and accuracy in manufacture.
Potentially, modular buildings can also be dismantled and
reused, thereby effectively maintaining their asset value. The
current range of applications of modular construction is in
cellular-type buildings, such as hotels, student residences,
Ministry of Defence (MoD) accommodation and social housing,
where the module size is compatible with manufacturing and
transportation requirements. The current application of
modular construction of all types is reviewed in a recent Steel
Construction Institute Publication 348 (Lawson, 2007). A paper
in The Structural Engineer (Lawson et al., 2005) describes the
mixed use of modules, panels and steel frames to create more
adaptable building forms.
There are two generic forms of modular construction, which
affect their range of application: load-bearing modules in
which loads are transferred through the side walls of the
modules – see Figure 1; and corner-supported modules in
which loads are transferred by way of edge beams to corner
posts – see Figure 2.
In the first case, the compression resistance of the walls
(comprising light steel C sections generally at 300 to 600 mm
spacing) is crucial. Current heights of modular buildings for
this type of construction are typically limited to four to eight
storeys, depending on the particular modular system and the
size and spacing of the C sections used.
In the second case, the compression resistance of the corner
posts is the controlling factor and for this reason, square hollo
w
sections (SHS) are often used owing to their high buckling
resistance. Building heights are limited only by the size of the
SHS that may be used for a given module size (150 3 150 3
12.5 SHS is the maximum sensible size of these posts).
Figure 1. Partially open-sided module with load-bearing walls
(courtesy PCKO Architects)
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 151
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Resistance to horizontal forces, such as wind loads and
robustness to accidental actions, becomes increasingly
important with the scale and height of the building. The
strategies employed to ensure adequate stability of modular
assemblies, as a function of the building height, are
(a) diaphragm action of boards or bracing within the walls of
the modules – suitable for four to six-storey buildings
(b) separate braced structure using hot-rolled steel members
located in the lifts and stair area or in the end gables –
suitable for six to ten storeys
(c) reinforced concrete or steel-plated core – suitable for taller
buildings.
Modules are tied at their corners so that structurally they act
together to transfer wind loads and to provide for alternative
load paths in the event of one module being severely damaged.
This is the scenario presented in Approved document A of the
Building Regulations (HMSO, 2006), which leads to minimum
tying force requirements. A recent paper (Lawson et al., 2008)
reviews the robustness requirements for modular
construction
based on a ‘localisation of damage’ route. Modules or load-
bearing elements are removed individually to assess the ability
of the rest of the assembly to support the applied loads at the
accidental limit state.
For taller buildings, questions of compression resistance and
overall stability require a deeper understanding of the
behaviour of the light steel C sections in load-bearing walls
and of the robust performance of connections between the
modules. A further issue in the design of modular construction
is that of installation and manufacturing tolerances, which
cause eccentricities in the compression load path and also lead
to additional horizontal forces applied to the modules. This is
considered later in the paper in the context of design to BS
5950-1 (BSI, 2000), which is the standard for structural
steelwork in buildings.
2. HIGH-RISE BUILDING FORMS USING MODULAR
CONSTRUCTION
Modular construction is conventionally used for cellular
buildings up to eight storeys high where the walls are load-
bearing and resist shear forces owing to wind. However, there
is pressure to extend this technology to high-rise buildings by
using additional concrete cores or structural frames to provide
stability and robustness.
One technique is to cluster modules around a core without a
separate structure in which the modules are designed to resist
compression and the core provides overall stability. This
concept has been used on a major project called Paragon in
west London, shown in Figure 3, in which the modules were
constructed with load-bearing corner posts (a paper on this
project was presented in The Structural Engineer (Cartz and
Crosby, 2007).
The building form may be elongated laterally provided that
wind loads can be transferred to the core. This can be achieved
by using in-plane trusses placed within the corridors, or by
consideration of the structural interaction between the modules
and their attachment to the core. Various alternative high-rise
building forms in which modules are clustered around a core
are presented in Figure 4.
An adaptation of this technology is to design a ‘podium’ or
platform structure on which the modules are placed. In this
way, more open space can be provided for retail or commercial
use or below-ground car parking. Support beams should align
with the walls of the modules and columns are typically
arranged on a 6 to 8 m grid (7.2 m is optimum for car parking),
as shown in Figure 5.
For the modular system covered by the tests reported in this
Figure 2. Open-sided module with corner and intermediate
posts supported by a structural frame (courtesy Yorkon and
Joule Engineers)
Figure 3. Modular building stabilised by a concrete core
(courtesy Caledonian Building Systems)
152 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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paper, three building projects have been completed to date
based on the enhanced modular technology. Bond Street,
Bristol is a 12-storey student residence and commercial
building in which six to ten storeys of modules sit on a two-
storey steel-framed podium (see Figure 6). The 400 bedroom
modules are 2.7 m external width, but approximately
100 modules are combined in pairs to form ‘premium’ studios
consisting of two rooms. The kitchen modules are 3.
6 m
external width. Stability is provided by four braced steel cores,
into which some modules are placed (Figure 7).
A second building, Pitwines in Poole, is an eight-storey student
residence comprising approximately 300 modules. Both
buildings use lightweight cladding attached to the walls of the
modules and comprise terracotta tiles or insulated render
cladding. The nature of the student residential sector is that the
construction period is often less than 12 months, and the
installation of modules is generally carried out in the January
to March period for a September completion. A further project
using this technology has been completed in east London and
another is under way in north London. This last project is
shown under construction in Figure 8.
Another modular manufacturer has developed a system using
1B
2P
2B4P
2B4P
2B4P
1B2P
2B4P
9
9
0
0
9
9
0
0
330033006000 6000 12001200
1
2
0
0
2B4P 2B4P
1B2P 1B2P
3B6P
1B2P 1B2P
9
9
0
0
24001200 120060006000
6
6
0
0
6
6
0
0
(a)
(b)
Figure 4. Typical high-rise building forms using modules and
concrete cores (courtesy HTA Architects) (2B4P means a
two-bedroom, four-person apartment for example): (a)
option 1A; (b) option 2
B
2·8 m Modules
Core for
stairs/lifts
300 mm
3–
3·6 m
300 mm
4·5
m
Spa
n of
12–
18 m
6 m
Figure 5. Modules supported by cellular beams acting as a
podium
Figure 6. Twelve-storey modular student residence at Bond
Street, Bristol (courtesy Unite Modular Solutions)
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 153
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SHS corner posts and a concrete floor with perimeter parallel
flange channel (PFC) steel sections. This has been used in eight
to eleven residential buildings, such as the one shown in Figure
9, and construction of taller buildings is in progress. In this
form of heavier modular construction, the effect of
construction tolerances on the forces acting on the corner posts
is much more important –see section 6.4.
3. DESIGN OF
MODULAR WALLS TO
BS 5950-5
Light steel walls and floors in
modular construction are
currently designed to
BS 5950-5 (BSI, 1998), but
interpretation of this standard
is required to take account of
the practical aspects of the
constructional system. In
modular systems with load-
bearing walls, the light steel
C sections in the walls are
subject to potentially
complex loading and
restraint conditions. In most cases, these conditions are as
outlined
below.
(a) Axial load is transferred by way of direct wall–wall
bearing, taking into account eccentricities in manufacture
and installation of the modules, which causes additional
build-up of moments and accentuates the local bearing
stresses at the base
of the wall.
(b) Loading from the floors and ceilings is taken as applied at
the face of the wall (at an eccentricity of half the wall
width), which causes additional local moments.
(c) Restraint is provided at the floor and ceiling positions so
that the effective height of the wall may be taken as its
clear internal height.
(d) Two layers of plasterboard or similar boards are attached to
the internal face of the wall by screws at not more than
300 mm spacing and provide up to 90 min fire resistance.
(e) Cement particle board (CPB) or oriented strand board (OSB)
are often attached to the exterior of the wall for weather-
tightness of the module and to provide some diaphragm
action. In production, boards may be fixed air-driven pins
enhanced by glued joints.
( f ) In taller modular buildings, second-order (P�˜) effects
may occur owing to sway and other eccentricities that are
often neglected in the design of low-rise buildings
The effects of axial loading and eccentricity can be taken into
account in the design of compression members to BS 5950-5
(BSI, 1998), but the stabilising effect of the boards on local and
overall buckling is largely unquantified. It is reasonable to
assume that boards fixed on both sides provide restraint in the
minor axis direction of the C section, but the stiffening effect
of the boards in the major axis (out-of-plane) direction is not
known, nor is the stabilising effect of boards attached only on
one side. This is the subject of the test programme described
below.
The following tests were carried out to verify the structural
action of the load-bearing walls in a typical modular system.
Two series of tests were carried out: one series on 75 mm
deep 3 45 mm wide 3 1.6 mm thick C sections at the Building
Research Establishment (BRE) and one series on 100 mm
deep 3 42 mm wide 3 1.6 mm thick C sections at the
University of Surrey.
Core
2
Core
4
Core
3
Core
1
Corridor
Corridor
Corr
idor
Separating wall
Premier room
modules
Separating wall
Standard
modules
Figure 7. Plan of modular building at Bond Street, Bristol showing the core positions
Figure 8. Eleven-storey modular student residence in north
London under construction (courtesy Unite Modular
Solutions)
Figure 9. Modular residential building, Wolverhampton
(courtesy Vision Modular Structures)
154 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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The tests were intended to establish the compression resistance
of the C sections, nominally placed at 300 mm spacing, taking
account of the restraining and stiffening effects of various
types of board. The sensitivity to eccentricities up to 20 mm
was also investigated, as this exceeds the maximum that may
be envisaged with good control on installation of modules in
practice.
The panels were loaded using a spreader beam and lateral
restraints in the form of PFC sections, and the test arrangement
is illustrated in Figure 10. The eccentricity in load application
was introduced by a 6 mm thick steel plate inserted at the base
of the wall.
The main variables were the type of boards that are attached
on one or both sides and the eccentricity in axial load.
Additional tests were included on taller walls to examine the
influence of slenderness. The boards were fixed using 2 mm
diameter air-driven nails at 200 mm centres, as used in
production of the wall panels. The boards were attached 2 mm
short of the web of the top and bottom track so that the boards
were not loaded directly.
OSB was attached externally and, in some tests, CPB was
included to assess the difference in restraint provided by the
two types of board. Two layers of 15 mm fire-resistant
plasterboard were used internally, as required for 90 min fire
resistance. In two of the tests,
this plasterboard was omitted.
The walls were first loaded up
to around 100 kN to represent
serviceability loading before
loading incrementally to
failure. Deflections were
recorded at the top of the wall
(vertically and horizontally)
and at mid-height
(horizontally). The test failure
loads are presented in Table 1.
The failure load generally
occurred at a relatively small
vertical displacement of less
than 5 mm.
A further series of tests was
carried out on 2300 mm
high 3 600 mm wide wall
panels, comprising three
100 mm deep C sections
with a mid-height noggin
built into the wall panel to
provide lateral restraint in
the minor axis.
Side B
Roller
Spreader
150 75 18
PFC
� �
150 75 18
PFC
� �
2450 mm
11 mm OSB 2 15 mm plasterboard�
75 1·6 C�
Lateral
restraint
Jack
Side A
Plate
150 75 18 PFC� �
1200 mm
150 75 18 PFC� �
(6 mm thick)
Plate
Figure 10. Test arrangement for BRE wall compression tests
Wall test details Wall height: m Eccentricity of
loading: mm
Failure load per C
section: kN
Design resistance to BS
5950-5: kN
Model
factor
75 3 45 3 1.6C:
OSB boards on one side only
2.45 0 64 48 1.33
75 3 45 3 1.6C:
Plasterboard on one side,
2.45 0 97 76 (inc. effect of boards) 1.27
OSB on the other 2.77 0 90 56 (inc. effect of boards) 1.61
2.45 10 79 56 (inc. effect of boards) 1.41
2.45 20 62 47 (crushing) 1.31
75 3 45 3 1.6C:
Plasterboard on one side, CPB
2.45 0 96 76 (inc. effect of boards) 1.26
on the other 2.45 20 52 47 (crushing) 1.10
100 3 42 3 1.6C:
Plasterboard on one side only
2.30 0 57 51 1.13
100 3 42 3 1.6C:
CPB on one side only
2.30 0 70 61 1.14
Model factor ¼ Failure load/design resistance
Table 1. Failure loads of C section wall studs and comparison with BS 5950-5
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 155
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Two additional bending tests were carried out on wall panels
using 75 3 1.6 C sections subject to a line load at mid-span.
The purpose was to calculate the effective stiffness of the wall
panels in order to calculate the modified slenderness of the
C section for the compression resistance to major axis buckling.
The cases considered were
(a) OSB board on one side and two layers of plasterboard on
the other (OSB in compression)
(b) OSB board on one side with no plasterboard on the other
(OSB in compression).
The measured values of Ieff taking into account the stiffening
effects of composite action with the boards were
432 3 103 mm4 and 270 3 103 mm4 per C section respectively.
The calculated second moment of area of the bare C section
was 265 3 103 mm4. It follows that the effective inertia is
increased by 62% for boards fixed on both sides but by only
2% for OSB board on one side.
The light steel walls were analysed in accordance with
BS 5950-5 using measured section dimensions and steel
strengths. Composite action occurred owing to the additional
stiffness of the boards attached to both sides, which increase
the buckling resistance of the wall. The section properties of
the C sections were calculated for the case where the edge lips
are considered to be fully effective.
The strip steel was S350 grade supplied to BS EN 10327 (BSI,
2004b) and measured strengths were in the range 380–405
N/mm2. Calculated compression resistances to BS 5950-5 are
presented in Table 1. The model factor is the ratio of the test
failure load to the compression resistance to BS 5950-5, based
on measured material strengths and geometry.
The attachment of boards to both sides of the wall effectively
prevents minor axis buckling, even for the narrow wall panels
tested and so failure may occur in one of three modes
(a) crushing of the cross-section locally in compression, as in
Figure 11
(b) buckling of the wall in the major axis direction, as in
Figure 12
(c) delamination of the boards from the wall studs, leading to
loss of composite action.
The stiffening effect of the boards leads to a reduction in
slenderness and increase in buckling resistance. Using the
measured 62% increase in bending stiffness of the wall panel,
the effective slenderness of the bare C section is reduced by
22% owing to attachment of the OSB and plasterboards. For a
2.45 m wall panel, the slenderness in the major axis direction
was 79, and so the effective slenderness becomes
0.78 3 79 ¼ 62. This leads to a buckling strength of
pc ¼ 263 N/mm2 according to Table 10 of BS 5950-5 when
using a Q factor (effective area/gross area) of 0.88.
The calculated compression resistance was 67 kN, which is
approximately 70% of the test result of 97 kN. This suggests
that the buckling curve for cold-formed sections used in
BS 5950-5 is conservative. In addition, local buckling of the
Figure 11. Local crushing of C section in compression tests
Figure 12. Wall failure by overall buckling in pure compression
156 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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flanges of C section may be reduced by the attachment of the
boards, which increases the effectiveness of the cross-section.
The eccentricity of load application using a plate below the
wall accentuates local crushing, as well as overall buckling.
The crushing resistance of the C section without consideration
of buckling is calculated from Aeff py. The reduced crushing
resistance owing to eccentric loading may be taken into
account by considering a reduced compression area, Aeff .
Because the buckling resistance is approximately 70% of the
crushing resistance, it follows that buckling will occur first
unless the crushing resistance is reduced by over 30%.
A 10 mm eccentricity caused a 19% reduction in load capacity
and a 20 mm eccentricity caused a 36% reduction in capacity.
However, in the tests, a 10 mm eccentricity did not reduce the
failure load below the theoretical buckling capacity.
The second series of tests on walls used 100 3 1.6C sections
with boards on one side only. These tests showed that minor
axis buckling is prevented by fixing to plasterboard for 1.6 mm
thick steel, but the increase in compression resistance relative
to BS 5950-5 was less than for the 75 mm deep sections. This is
attributable to the lower transverse bending stiffness of the
web of the deeper C section, which means that the unsupported
flange is only partially restrained.
6. STRUCTURAL ACTION OF GROUPS OF
MODULES
The structural behaviour of an assembly of modules is complex
because of the influence of the tolerances that are implicit in
the installation procedure, the multiple interconnections
between the modules and the way in which forces are
transferred to the stabilising elements such as vertical bracing
or core walls. The key factors to be taken into account in the
design of high-rise modular buildings are
(a) the influence of initial eccentricities and construction
tolerances on the additional forces and moments in the
walls of the modules
(b) application of the design standard for steelwork, BS 5950-1
to modular technology, using the notional horizontal load
approach
(c) second-order effects due to sway stability of the group of
modules, especially in the design of the corner columns
(d) mechanism of force transfer of horizontal loads to the
stabilising system, for example concrete cores
(e) robustness to accidental actions (also known as structural
integrity) for modular systems.
These aspects are now discussed in turn.
6.1. Influence of constructional tolerances
The
National Structural Steelwork Specification for Building
Construction (NSSS) (BCSA, 2007) presents the permitted
tolerances of steel frames, in which the maximum out-of-
verticality of a single column is �H < height/600, but < 5 mm per storey. Furthermore, for steel-framed buildings of more
than ten storeys high, the maximum out of verticality over the
total building height is limited to 50 mm in the NSSS.
BS EN 1090-2 (BSI, 2008) concerns the execution of structures
and in it, the essential tolerances define the maximum
deviations that are permitted so as not to impair the overall
performance of a structure or member. BS EN 1090-2 Table
D.1.12, referring to multi-storey frames, differs from the NSSS
in that the cumulative error over n floors each of height h is
given by h
ffiffiffi
n
p
=300. It follows that the permitted cumulative
deviation over n storeys is 10
ffiffiffi
n
p
mm (for h ¼ 3 m) to BS EN
1090-2.
These permitted deviations for steel frames may not, however,
reflect the practicalities involved in modular construction
because of the difficulties in precisely positioning one module
on another and in making suitable connections. For a single
module placed on another module, it is proposed that the
maximum out of alignment during installation may be taken as
12 mm in orthogonal plan directions relative to the top of the
module below. This alignment requires careful control on site,
especially in windy conditions.
For a vertical stack of modules, the cumulative positional error,
e, owing to installation can be partially corrected over the
building height. Using the same logic as in BS EN 1090-2, the
cumulative positional tolerance (in millimetres) may be taken
statistically as e < 12 ffiffiffi n
p
, where n is the number of modules in
a vertical group. Typically, for n ¼ 10, the total cumulative
positional tolerance that is permitted becomes approximately
40 mm, but this neglects the geometric tolerances in the
module manufacture.
An alternative simplified procedure that is easier to control on
site is to limit the cumulative positional tolerance to 5 mm per
module in orthogonal directions with a maximum of 50 mm
(for n ¼ 10), which is similar to the NSSS. However, it is
considered that the maximum positional error of one module
on another may be taken as 12 mm (except at ground level
where a maximum of 5 mm should be achievable). This means
that at the first floor, the cumulative tolerance of 10 mm will
control, even if the first-floor module is 12 mm out of position
relative to the base module and the base module is positioned
at < �2 mm from datum.
Added to this positional error is the possibility of a systematic
manufacturing error in the geometry of the modules. For a
single module, the maximum permitted tolerance in geometry
may be taken as illustrated in Figure 13. However, over a large
number of modules, the average error in manufacture may be
taken as half of the permitted tolerance for a single
module.
Therefore, the out of verticality of the corner posts may be
taken as h/1000, where h is the module height (typically 3 m).
To take account of manufacturing tolerances, the cumulative
out of verticality over the building height may be taken as
nh/1000, or approximately 3n mm. The total permitted out-
of-verticality �H over the building height, consisting of a
stack of n modules vertically, is therefore a combination of
positional and geometric tolerances, approximately as
follows
�H < e þ nh=1000 ¼ 5n þ 3n ¼ 8n mm1
Using this simplified formula, it follows that �H ¼ 80 mm for
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 157
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n ¼ 10 storeys, which is equivalent to approximately h/350 per
floor. This is 60% higher than the tolerance permitted for
structural steelwork and reflects the different installation and
connection methods between structural frames and a group of
modules.
It is recommended that the absolute out of verticality in
modular construction is limited to a maximum of 80 mm
relative to a ground datum, which will control for buildings of
ten or more storeys. This is achievable with good control on
installation. Adjustments in module position should be made
gradually rather than at a few positions, which would
otherwise add to local eccentricities. These adjustments can be
made by varying the cavity spacing between the modules. In
detailing, the cavity width should be at least equal to half of
the expected maximum tolerance, or as a simple rule, taken as
a minimum of 40 mm.
6.2. Application of notional horizontal forces in modular
construction
A way of assessing the sway stability of a group of modules is
by using the notional horizontal force approach given in clause
2.4.2.3 of BS 5950-1. For steel frames, this horizontal force
corresponds to 0.5% of the factored vertical load acting per
floor, and is used in the absence of wind loading. It represents
the minimum horizontal force that is used to assess the sway
stability of a frame. A further limit for the combination of
wind and vertical load is that the wind load should not be less
than 1% of the factored dead load acting horizontally. This
may control where the self-weight exceeds the imposed loading
on a floor.
BS EN 1993-1-1 Eurocode 3 clause 5.3.2 (BSI, 2004a) permits
an out-of-verticality of L/200 for a single column, but this is
reduced by a factor of 2/3 when considering the average over a
number of storeys (i.e. �H < L/300). The permitted out of verticality of a whole structure is obtained by multiplying this
value for a single column by a factor of f[0:5 [1 þ (1=m)]g0
:5
for m columns in a group horizontally. The result tends to
�H < L/420, which is higher than in the NSSS, but further requirement in the approach of Eurocode 3 is that this out of
verticality is considered in combination with wind loading
rather than as an alternative load case, as in BS 5950-1.
The combined eccentricity on a vertical assembly of modules
takes into account the effects of eccentricities of one module
placed on another, and the reducing compression forces on the
walls acting at the increased eccentricity with height. This effect
is illustrated in Figure 14. The walls of the module are unable to
resist high moments owing to these effects and so the equivalent
horizontal forces required for equilibrium are transferred as
shear forces in the ceiling, floors and end walls of the modules.
The total additional moment acting on the base module is
therefore given by an effective eccentricity ˜eff multiplied by
the compression force in the base module, as follows
� h/500
h Bow /1000� hOut of
verticality
/500� h
Datum position
Idealised dimensions
Actual
dimensions
of module
Width
tolerance
/500� h
Length tolerance /500� h
Figure 13. Permitted maximum geometric errors in
manufacture of modules
P
� �
� �
� �
1
2
1000
e
h
�P
P
P
P
P
P
∆3
∆2
∆1
h
P( 1)/n n�
P( 2)/n n�
P P
e1 M P� e
e3
e2
V
V
1:1000 1:1000
(a) (b)
Figure 14. Combined eccentricities acting on the ground-floor modules: (a) shear in end walls due to eccentric loading for a
four-sided module; (b) transfer of eccentric loading to stabilising system for corner-supported modules
158 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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Madd ¼ Pwall˜eff
¼ Pwall
(n � 1)
n
þ 2
(n � 2)
n
þ 3
(n � 3)
n
. . . þ
1
n
� �
3 (e þ h=1000)
2
where Pwall is the compression force at the base of the ground-
floor module ¼ nWu, n is the number of modules in a vertical
assembly, e is the average positional eccentricity per module, h
is the module height (in mm), and Wu is the factored load
acting on each module.
As a good approximation, it is found that the following
formula holds for the effective eccentricity of the vertical stack
of modules as a function of n:
˜eff ¼
n � 1
6
� �
8n3
The effective base eccentricities are presented in Table 2 for
n ¼ 6 to 12 storeys and for a module height, h ¼ 3 m. This
eccentricity may be converted to a notional horizontal force
applied at each floor level, which is expressed as a percentage
of the vertical load acting at each floor level, and is defined as
the force which causes the same equivalent moment in the base
module as the effective eccentricity in Equation 2. This
moment is given by
kWun
2 h=2 ¼ Pwall˜eff ¼ nWu˜eff4
where k is the proportion of the factored load acting on each
floor, and so
k ¼
8(n � 1)
3h
� �
or
n � 1
3n
� �
80
h
� �
for n . 105
From Table 2, and using the tolerances defined above, it is
calculated that the notional horizontal force varies from 0.5% to
0.9%, when expressed as a percentage of the vertical load
applied to the module. It should be noted that k ¼ 0.5%, when
the maximum tolerance is 50 mm, which agrees with BS 5950-1.
For modular construction, it is therefore recommended that the
notional horizontal force is taken as a minimum of 1% of the
factored vertical load acting on each module, which reflects the
higher tolerances that are permitted in modular construction. It
is used as the minimum horizontal load in assessing overall
sway stability of the structure, and it is proposed that it is used
in combination with wind forces.
As an example, for a module of 25 m2 floor area subject to
factored loading of 7 kN/m2, the notional horizontal force
acting in orthogonal directions is approximately 2 kN. For a
vertical stack of ten modules, the base shear is therefore 20 kN.
This shear force may be shared between the two walls of the
module in the direction under consideration. The notional force
may be compared with a wind load of up to 10 times this
magnitude acting as a shear on the longitudinal side façade of
the building, and so is still relatively small. The notional
horizontal force may, however, control when there are less
than 10 modules in a horizontal group.
If the modules are unable to resist the horizontal force required
for overall stability, the forces must be combined for a number
of modules on plan at each level and transferred to the
stabilising system. This may be the case for partially open-
sided modules.
6.3. Forces at module interconnections
The structural interactions within a group of modules are
complex. Horizontal forces may be transferred by tension and
compression forces in the ties at the corners of the modules by
utilising the diaphragm action of the base and ceiling of the
modules. Shear forces may be transferred through the
continuous corridor members rather than the corner
connections because of the potential articulation through the
bolts and connecting plates between the modules. These actions
are illustrated in Figure 15.
Where the corridor floor is used to transfer shear forces, the
connection of the modules to the corridor may be made by a
detail of the form of Figure 16. The extended plate is screw
fixed on site to the corridor members and is bolted to the re-
entrant corners between the modules so that it also acts as a tie
plate. This detail is not used to provide vertical support to the
corridor floor, which is supported on continuous angles
attached to corridor wall of the modules.
The forces in the tie connection in Figure 16 may be calculated
on the basis of the wind forces acting on the module. The
highest force occurs for an external pressure coefficient of
+0.85 and a negative internal pressure of �0.3. The wind force
on one module is divided between two module-to-corridor
connections. For a wind pressure of 1.2 kN/m2, the force in this
connection is approximately 8 kN at working loads.
The shear attachment to the core is made both through the
corridor and also at the module adjacent to the core. This
Number of
modules
Approx. building
height: m
Cumulative out-of-verticality
at top of building: mm
Effective eccentricity on base
module – Simplified formula in
Equation 3: mm
Notional horizontal force
Equation 5: %
n ¼ 6 16 48 5/6 3 48 ¼ 40 0.5
n ¼ 8 22 64 7/6 3 64 ¼ 75 0.7
n ¼ 10 27 80 9/6 3 80 ¼ 120 0.9
n ¼ 12 33 80 11/6 3 80 ¼ 147 0.9
Table 2. Summary of effective eccentricities and notional horizontal forces in modular construction as a function of building height
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 159
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connection force at the core is designed for the aggregate of
the module–corridor connection forces, which for a group of
three to four modules is 24 to 32 kN (factored loading ) or 18
to 24 kN as a working load.
6.4. Stability of corner posts in modular construction
Corner posts add to the compressive resistance of a wall and, if
they are included in the module, it is normal practice to
assume that all the applied vertical loads acting on the module
are resisted by the corner posts. These posts are usually in the
form of steel angle sections for low-rise applications, or SHSs
for taller buildings. The posts are effectively restrained from
buckling by the in-plane stiffness of the walls of the modules
to which they are connected, but this assumption may not be
valid for partially open-sided modules or for highly perforated
walls.
Consider the stability of the corner posts of a module when
restrained only by the in-plane stiffness of the walls of the
module, as illustrated in Figure 17. The posts are discontinuous
at the module–module connections and do not contribute to
the sway stiffness of the structure, but are restrained against
buckling in their height between the connection points.
The initial out of verticality of the corner post increases under
an axial load, P, in each post, which may be approximated by
strut buckling theory, according to
� ¼
�o
1 � 2P=Pcritð Þ
6
where P is the axial compression acting on one post; �o is the
initial out of verticality and eccentricity of the corner post; Pcrit
is the critical buckling resistance for sway stability of the
module.
From this simple shear failure mechanism, the work done in
Module
(a)
θ
Tie
L
B
Tie in corridor
(b)
Forces
in ties
Module
Figure 15. Force transfer between modules: (a) force transfer
at corridor – bending action; (b) force transfer at corridor –
pure shear
80
7030 gap
Bolt hole
Upper module
Lower module
(a)
(b)
Figure 16. Connection detail between the corridor cassette
and modules: (a) sketch detail; (b) actual detail
160 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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shear and compression may be equated, in order to determine
the critical buckling load, Pcrit, as follows
k˜2
2
¼
2Pcritð Þ˜2
2h
or Pcrit ¼ 0:5kh7
where k is the shear stiffness of the wall panel.
As P approaches Pcrit, so the shear deflection of the wall panel
increases rapidly. Therefore, it is necessary to keep P well
below Pcrit to avoid instability effects. The eccentricity of load
causes both bending in the post and shear in the wall panel.
The shear stiffness of the wall can be estimated from shear
diaphragm tests and corresponds to the horizontal load at a
serviceability deflection of h/500, where h is the module height
in millimetres. This is achieved for a shear force of typically
(a) 10 kN for a 2.4 m wide wall panel with a window, or
approximately 4 kN/m width
(b) 20 kN for a 2.4 m wide unperforated panel, or
approximately 8 kN/m width.
In the case of a module with h ¼ 3 m and width of b ¼ 3.6 m,
it follows that the typical shear stiffness of an end wall panel
with a window becomes
k ¼
4 3 3:6 3 500
3:0
¼ 2400 kN=m
Inserting this value of k in Equation 7 leads to a critical
buckling load owing to shear in the end wall of a module of
Pcrit ¼ 0:5 3 2400 3 3 ¼ 3600 kN
To check the stability of the corner post, it is recommended
that the eccentricity in load application is taken as the
maximum positional eccentricity of 12 mm when one module
is placed on another plus the maximum out of verticality in
manufacture of a single module (or h/500, as shown in Figure
13). For a 3 m high module, �o ¼ 12 + 6 ¼ 18 mm. These
eccentricities are illustrated in Figure 18.
In addition, a local moment is transferred from the floor or
edge beam, which may act in the same sense as the positional
eccentricity. For a floor–wall junction, this shear load may be
assumed to act at the face of the wall studs (or a minimum of
50 mm). For a corner post, the shear load acts at the centre of
the bolt group, and a minimum eccentricity of 75 mm from the
centre of the post may be used. This local moment acts only on
individual modules and is not cumulative.
The additional moment acting on a corner post is calculated
from M ¼ P�, where � is given by Equation 6. For a wall, the
effective eccentricity also includes the bow in the wall between
the corners (or h/1000, as shown in Figure 14).
For a corner post, the effective eccentricity is therefore given
by �o ¼ 18 + 75/n mm. For a load-bearing wall, the effective
eccentricity is given by �o ¼ 21 + 50/n mm. For n ¼ 10, the
effective eccentricities become approximately 25 mm in both
cases.
The stability of a corner post is then checked as
P=Pc þ M=Mc < 1:08
where P is the load acting at the top of the base module and Pc
is the compression resistance of the post.
When the post is restrained against buckling in its height by
attachment to the adjacent walls, then the bending resistance
may be taken as Mc ¼ Mel, where Mel is the elastic bending
resistance of the post. Elastic properties should be used in order
to take account of uncertainties in this simple linear interaction
method in Equation 8.
For an unsupported post (not restrained by the walls), the
compression resistance is given by Pc ¼ pcA, where pc is
calculated from the minor axis slenderness of the post and Mc
B
P P
H
2P
∆
K
φ
Figure 17. Sway stability of the wall of a module for corner
posts in compression
Pmax
( 1)n �
nPmax
( 1)n �
n
Wall of
module
Floor
Floor
φ 0·002�
� /500h
Ceiling
Mfloor
Pmax Pmax
b
w
h
Mfloor � 0·25 wbd
d
e
Figure 18. Illustration of eccentricity of forces applied to the
walls or corner posts of a module
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 161
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is the bending resistance for lateral torsional buckling. The
interaction equation is also modified to take into account
bending in two directions, as in BS 5950-1.
As an example for a 7.2 m long 3 3.6 m wide module, with a
factored floor load of 7 kN/m2, the compression force acting at
the top corner of the ground-floor module in a 12-storey
building is approximately
P ¼ 7 3 7:2 3 3:6 3 (12 � 1)=4 ¼ 499 kN
Check the compression resistance of the corner posts using
100 3 100 3 10 SHS (in S355 steel), which are stabilised by
the walls of the modules: crushing resistance, Py ¼ 1239 kN,
and bending resistance, Mel ¼ 32.8 kN m.
The out-of-plane displacement and its associated moment, M,
are obtained from Equation 6
�o ¼ 18 þ 75=n ¼ 25 mm
� ¼
25
1 � 2 3 499=3600ð Þ
¼ 34 mm
M ¼ 499 3 0:034 ¼ 17:0 kN m
Using the linear combination of axial force and moment for
member stability
P=Pc þ M=Mel ¼ 499=1239 þ 17:0=32:8
¼ 0:40 þ 0:52 ¼ 0:92 , 1:0
It follows that the effect of eccentricity in installation and out
of verticality in manufacture is to reduce the compressive
resistance of a corner post by about 60%. It is also
recommended that for simple design, the effective eccentricity
of load acting on the corner post is taken as not less than
35 mm, which allows for a 40% magnification in sway from
the initial eccentricity of 25 mm.
6.5. Robustness to accidental damage
The ability of an assembly of modules to resist applied loads in
the event of serious damage to a module at a lower level is
dependent on the development of tie forces at the corners of
the modules. The loading at this so-called accidental limit state
is taken as the self-weight plus one third of the imposed load
all multiplied by a partial factor of safety of 1.05 to BS 5950-1.
To satisfy ‘robustness’ in the event of accidental damage to one
of the modules, the tie forces between the adjacent modules
may be established on the basis of a cantilever model, as
presented in a recent paper (Lawson et al., 2008). Assuming
that the worst case corresponds to loss of support to one side of
a corner module and that each module above is able to develop
tying forces equally, the tension force in the ties is given as
follows
T ¼
Wab
4h
� �
9
where Wa is the load acting on the module at the accidental
limit state, and b and h are the dimensions of narrow end of
the module.
Figure 19 shows the results of a finite-element analysis of a
module when one corner support is removed, which is a more
likely case than complete removal of one side wall. The applied
load is taken as 10 kN/m per wall for a heavyweight module
using the partial factors noted above. Torsional stiffness of the
module is developed by diaphragm action of the walls and
floor/ceiling. From this analysis, the maximum horizontal tying
force is equal to 26% of the total load applied to the module
(rather than 48% in the cantilever formula) and the maximum
vertical load is approximately 40% of the total load. It is
concluded that the minimum values of the horizontal tying
force, T, may be taken as 30 kN for lightweight modules (self-
weight , 3.5 kN/m2) or 50 kN for heavyweight modules (self-
weight , 6 kN/m2).
6.6. Module connection tests
As part of the development programme for the modular
supplier, tests on complete modules were carried out at the BRE
to assess the tensile resistance of the tie detail between the
corridor cassette and the corner of the module. The tie
connection is made at the re-entrant corner of the module.
The module was held in place at two corners and a tensile force
was applied at the top opposite corner causing pull-out of the
connecting bolt to the 4 mm thick corner angle manufactured
as part of the module. Forces within the module are transferred
by way of in-plane diaphragm action of the ceiling and walls.
A rigid corner gusset plate was attached across the junction
between the bottom track and the end wall stud, and the
tension force reached of 40 kN at failure corresponding to a
displacement of 10 mm. The gusset detail at a load level of
25 kN is shown in Figure 20. The load–deflection graph for
this test is shown in Figure 21.
27 kN
5 kN
1 kN
56 kN
27 kN
5 kN
1 kN
38 kN
38 kN
50 kN
38 kN
3·6 m
2·7 m
10 kN/m
10 kN/m
Deflected shape
7·2 m
32 mm
vertically
Figure 19. Illustration of tie forces when support to one
corner of a module is removed
162 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
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The test using a stiffening plate at the corner of the module
showed that this arrangement offers the best solution for the
module-to-corridor connection. The characteristic resistance of
this connection is taken as 20% less than the failure load of a
single test, or 0.8 3 40 ¼ 36 kN, which exceeds the calculated
load of 24 kN for transfer of wind forces across three modules
to an adjacent core.
This paper presents the results of tests on light steel walls in
compression, which are used to demonstrate the extension of
modular construction up to 12 storeys high. The tests showed
that the stiffening effect of the fascia boards is very high and
that the compression resistance of the C sections is increased in
comparison to the bare steel section. These conclusions refer to
internal wall heights of 2.3 to 2.8 m using 75 mm to 100 mm
deep C sections.
(a) Minor axis buckling is effectively prevented by attachment
of various types of boards on one side only, provided the
steel thickness is not less than 1.6 mm.
(b) The test load capacities exceeded the design resistance to
BS 5950-5 by 10 to 40% due to the stiffening effects of the
attached boards.
(c) The effective bending stiffness of the bare steel sections is
increased by up to 62% due to the attachment of OSB and
CPB boards on both sides.
(d) The effect of 10 mm out-of-plane eccentricity in load
application reduces the failure load by 19%, and the effect
of 20 mm out-of-plane eccentricity accentuates local
crushing and reduces the failure load by 18 to 36%.
The tests on the module-to-module connections showed that a
tying force of 40 kN can be resisted. For robustness to
accidental actions, the minimum tying force between modules
should be taken as 30 kN for lightweight modules (self-weight
, 3.5 kN/m2) and 50 kN for heavyweight modules.
The effect of installation and geometric inaccuracies must be
taken into account in the design of modular buildings. It is
proposed that the maximum positional error is 12 mm for one
module placed on another. When combined with
manufacturing tolerances, it is proposed that the maximum out
of verticality should not exceed 8 mm per module in a vertical
group (or an absolute maximum of 80 mm) relative to ground
datum. Using these tolerances, the notional horizontal force
used to evaluate stability of a group of modules should be
taken as a minimum of 1% of the applied vertical load on the
modules, which acts in combination with wind loading but at
reduced load factors.
For modules designed with corner posts, it is shown that an
additional effect owing to the shear flexibility of the end walls
has to be taken into account when calculating the moments
acting on the posts due to sway effects. The minimum
eccentricity for design of the corner posts should not be less
than 35 mm taking account of second-order effects, and the
minimum eccentricity for design of load-bearing side walls
should not be less than 25 mm.
The structural testing at the Building Research Establishment
was funded by Unite Modular Systems Ltd as part of their
development strategy. The contribution of Dave Brooke and the
team in the Heavy Structures Lab at BRE is gratefully
acknowledged. Additional wall tests at the University of Surrey
were funded by Metek UK Ltd.
BCSA (British Constructional Steelwork Association) (2007)
National Structural Steelwork Specification for Building
Construction, 5th edn. BCSA, London.
BSI (British Standards Institution) (1998) Structural Use of
Steelwork in Building. Code of Practice for Design of Cold
Formed Thin Gauge Sections. BSI, London, BS 5950: Part 5.
BSI (2000) Structural Use of Steelwork in Building. Code of
Figure 20. Tensile test on module with stiffening plate
�1
0·00
0·00
10·00
20·00
30·00
40·00
50·00
�5 0 5 10 15 20 25 30
Deflection mm
L
o
a
d
:
kN
Figure 21. Load–displacement results for module test with
stiffening plate. Unite module corner test 7
Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards 163
Downloaded by [] on [12/12/18]. Copyright © ICE Publishing, all rights reserved.
Practice for Design of Simple and Continuous Construction:
Hot Rolled Sections. BSI, London, BS 5950 Part 1.
BSI (2004a) Eurocode 3: Steel Structures – General Rules and
Rules for Buildings. BSI, London, BS EN 1993-1-1.
BSI (2004b) Specification For Continuously Hot-dip Zinc Coated
Structural Steel and Strip – Technical Delivery Conditions.
BSI, London.
BSI (2008) Execution of Steel Structures and Aluminium
Structures. Part 2 Technical Requirements for Execution of
Steel Structures. BSI, London, BS EN 1090-2.
Cartz JP and Crosby M (2007) Building high-rise modular
homes. The Structural Engineer 85(l9): 20–21.
HMSO (2006) England and Wales Approved Document A.
HMSO, London
Lawson RM (2007) Building design using modules. The Steel
Construction Institute, London, Publication 348.
Lawson RM, Ogden RG, Pedreschi R, Popo-Ola S and Grubb J
(2005) Developments in pre-fabricated systems in light steel
and modular construction. The Structural Engineer 83(6):
28–35.
Lawson RM, Byfield M, Popo-Ola S and Grubb J (2008)
Robustness of light steel frames and modular construction.
Proceedings of the Institution of Civil Engineers, Buildings
and Structures 161(1): 3–16.
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164 Structures and Buildings 163 Issue SB3 Modular design for high-rise buildings Lawson • Richards
Downloaded by [] on [12/12/18]. Copyright © ICE Publishing, all rights reserved.
- 1. INTRODUCTION
- 2. HIGH-RISE BUILDING FORMS USING MODULAR CONSTRUCTION
- 3. DESIGN OF MODULAR WALLS TO BS 5950-5
- 6. STRUCTURAL ACTION OF GROUPS OF MODULES
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
4. COMPRESSION TESTS ON MODULAR WALLS
Figure 7
Figure 8
Figure 9
Figure 10
Table 1
5. ANALYSIS OF WALL TESTS TO BS 5950-5
Figure 11
Figure 12
6.1. Influence of constructional tolerances
Equation 1
6.2. Application of notional horizontal forces in modular construction
Figure 13
Figure 14
Equation 2
Equation 3
Equation 4
Equation 5
6.3. Forces at module interconnections
Table 2
6.4. Stability of corner posts in modular construction
Equation 6
Figure 15
Figure 16
Equation 7
Equation 8
Figure 17
Figure 18
6.5. Robustness to accidental damage
Equation 9
6.6. Module connection tests
Figure 19
7. CONCLUSIONS
ACKNOWLEDGEMENTS
Figure 20
Figure 21
REFERENCES
BCSA 2007
BSI 1998
BSI 2000
BSI 2004a
BSI 2004b
BSI 2008
Cartz and Crosby 2007
HMSO 2006
Lawson 2007
Lawson et al. 2005
Lawson et al. 2008
sustainability
Review
Performance of Modular Prefabricated Architecture:
Case Study-Based Review and Future Pathways
Fred Edmond Boafo 1, Jin-Hee Kim 2 and Jun-Tae Kim 3,*
1 Zero Energy Buildings Laboratory, Graduate School of Energy Systems Engineering,
Kongju National University, Cheonan, Chungnam 330-717, Korea; febs@kongju.ac.kr
2 Green Energy Technology Research Center, Kongju National University, Cheonan, Chungnam 330-717,
Korea; jiny@kongju.ac.kr
3 Department of Architectural Engineering & Graduate School of Energy Systems Engineering,
Kongju National University, Cheonan, Chungnam 330-717, Korea
* Correspondence: jtkim@kongju.ac.kr; Tel.: +82-41-521-9333
Academic Editor: Marc A. Rosen
Received: 9 May 2016; Accepted: 13 June 2016; Published: 15 June 2016
Abstract: Even though tightened building energy efficiency standards are implemented periodically
in many countries, existing buildings continually consume a momentous quota of the total primary
energy. Energy efficiency solutions range from material components to bulk systems. A technique of
building construction, referred to as prefabricated architecture (prefab), is increasing in reputation.
Prefab encompasses the offsite fabrication of building components to a greater degree of finish as
bulk building structures and systems, and their assembly on-site. In this context, prefab improves
the speed of construction, quality of architecture, efficiency of materials, and worker safety, while
limiting environmental impacts of construction, as compared to conventional site-built construction
practices. Quite recently, a 57 story skyscraper was built in 19 days using prefabricated modules.
From the building physics point of view, the bulk systems and tighter integration method of prefab
minimizes thermal bridges. This study seeks to clearly characterize the levels of prefab and to
investigate the performance of modular prefab; considering acoustic constrain, seismic resistance,
thermal behavior, energy consumption, and life cycle analysis of existing prefab cases and, thus,
provides a dynamic case study-based review. Generally, prefab can be categorized into components,
panels (2D), modules (3D), hybrids, and unitized whole buildings. On average, greenhouse gas
emissions from conventional construction were higher than for modular construction, not discounting
some individual discrepancies. Few studies have focused on monitored data on prefab and occupants’
comfort but additional studies are required to understand the public’s perception of the technology.
The scope of the work examined will be of interest to building engineers, manufacturers, and energy
experts, as well as serve as a foundational reference for future study.
Keywords: prefabricated architecture (prefab); modular; energy; thermal behavior; acoustic
constraints; seismic resistance; life cycle analysis
1. Introduction
1.1. Background
Vis-à-vis the automobile, shipbuilding, and aerospace industries, the building construction
industry has been the slowest to change over the years. That premise may be about to change at a
startling pace. Quite recently, a Chinese company has built a 57 story, 800 apartment skyscraper (called
Mini Sky City) in just 19 working days in the Hunan provincial capital of Changsha. Mini Sky City
was roofed on 17 February 2015. The builders, Broad Sustainable Building, were able to get Mini
Sustainability 2016, 8, 558; doi:10.3390/su8060558 www.mdpi.com/journal/sustainability
http://www.mdpi.com/journal/sustainability
http://www.mdpi.com
http://www.mdpi.com/journal/sustainability
Sustainability 2016, 8, 558 2 of 16
Sky City ready so quickly for occupants by assembling the skyscraper out of prefabricated sections
using modular methods; fabricating the building’s 2736 modules for 4.5 months before construction
began at an installation rate of three floors per day [1,2]. Inside Mini Sky City is the world’s first
indoor spiraling sky street 3.6 km upwards from the first floor to the roof garden on the 57th floor [3].
Time savings attributed to prefabricated construction revolve around the fact that on-site foundation
construction can be done in parallel to offsite component fabrications, while restraining weather delays
on the construction schedule [4,5].
From a single prefabricated window system to an intricate prefabricated building module, almost
all contemporary buildings integrate prefabrication to a degree. Particularly, prefabricated architecture
is an offsite manufacturing process that takes place at a specialized facility in which various materials
and building systems are joined to form a component or part of a larger final assembly on-site, or a
unitized building system to be installed on-site. Industrialized building, offsite construction, offsite
fabrication, prebuilt construction, and prefabricated building are some terms used interchangeably
in literature to describe prefabricated architecture—hereafter referred to as prefab. Significant
research activities have focused on various aspects of prefabricated buildings, namely: realizing lean
construction through off-site manufacturing [6–8], surveying the perspective of housebuilders on offsite
construction trends [9], opportunities and constraints of offsite construction [10–12], policy-making [13],
design solutions [14], software implementation potential [15–17], and future perspectives [18,19].
The recent UNFCCC COP 21 resolved to restrain increases in global average temperature to below 2 ˝C
by reducing emissions, among others, towards sustainable development [20]. Prefabrication is said
to be a sustainable building technology [21]. The benefits of adopting prefabrication in building
construction can be quantified through survey and comparative analysis from stakeholders and
selected existing buildings. Studies support that construction quality and safety can be increased
with prefabrication, while time spent for construction completion, overall costs, material waste, and
the impact on the environment can be reduced [11,22–25]. Designing with prefab components is
not a barrier to creativity; conversely, by standardizing prefab components and providing mass
customization options, ultimately lowers final costs through economies of high volume work [26,27].
For instance, in Hong Kong, the construction industry generates a huge quantity of waste and this
amount reaches 40% of the total waste intake at the landfill areas; space for waste disposal is running
out and prefabrication in construction is being turned to with a promising waste reduction of 84.7% [28].
The benefits of applying prefabrication were considered as having different levels of significance to
construction, and a survey was conducted to identify the level of recognition of these beneficial aspects.
Better supervision on improving the quality of prefabricated elements ranked as first with an
average value of 4.09. The respondents claimed that prefabrication of building components achieved
better quality products with better supervision, as the prefabricated elements were tested and inspected
before site installation. Frozen design at the early stage for better adoption of prefabrication and
reduced overall construction costs were ranked second and third, respectively, with average values
of 3.91 and 3.63, respectively. Additionally, the respondents argued that other than the cost that can be
saved from the early standardized design layout, time can also be reduced as the prefabrication can
increase the productivity and efficiency of building construction; this interpretation is in line with the
survey’s result of ranking fourth of the advantages of prefabrication with an average value of 3.50 [28].
A further study reiterated that adopting prefabrication demonstrated significant advantages, such as
improved quality control, reduction of construction time (20%), reduction of construction waste (56%),
and reduction of dust and noise on-site, as well as labor required on-site (9.5%) [29]. For a 25 story
student residence in Wolverhampton, UK, with 16, 340 m2 total floor area worth of modules, the
installation period was 32 weeks for 824 modules and the total man-hours of on-site work was
estimated as 170,000 (or approximately 8.2 man-hours per m2 of the completed floor area). It was
estimated that the reduction in the construction period relative to site-intensive concrete construction
was over 50 weeks (or a saving of 45% in construction period). In addition, a 70% reduction in
waste relative to site-intensive concrete construction was estimated [30]. Post-occupancy and indoor
Sustainability 2016, 8, 558 3 of 16
monitoring surveys of prefabricated timber housing showed that the indoor temperature rose above the
comfort range when external temperature was above 19 ˝C [31]. To comprehensively understand the
actual performance of prefab, monitoring and measurement of existing prefab needs to be quantified
and declared, which will also boost the confidence of all stakeholders involved. The objective of this
study is to examine the general performance of modular prefabricated buildings based on existing cases
and, thus, provide a dynamic case study-based review. As a precedent, an overview of the different
levels of prefabrication in buildings and its historic development is clearly presented. Ultimately,
this study seeks to identify performance boundaries of prefab based on an analysis of selected cases.
Most literature on prefab focused on their architectural designs, general descriptions, and construction
specifications. This study will be knowledgeable to stakeholders involved in the building industry
and, as such, serve as a foundational reference for future work on the subject. However, unpublished
or inadequate data of numerous existing prefab limits the scope of this work.
1.2. Brief History of Prefab
Prefabrication in the construction industry is evolutionary, not revolutionary, based on successful
and unsuccessful experiences [4]. The earliest prefabricated cases was recorded in 1624, when houses
were prepared in England and sent to the fishing village of Cape Ann, in what is now a city in
Massachusetts. In 1790, simple timber-framed shelters were shipped from England to Australian
settlements in New South Wales as hospitals, storehouses and cottages. Years later, a similar system
was erected in Freetown, Sierra Leone and Eastern Cape Province of South Africa; these structures
were simple and shed-like, with timber frames, clad either with weatherboarding or board-and-batten
siding. Although these structures were not extensively prefabricated, they represented a significant
reduction in labor and time compared to on-site methods then. In 1830, the Manning Portable Colonial
Cottage for emigrants, an improvement of the earlier system, was developed. The house was an
expert system of prefabricated timber frame and infill components, designed to be mobile and easily
shipped. 1833 was the beginning of the light balloon frames in the United States; buildings were
erected so quickly that Chicago was almost entirely constructed of balloon frames before the infamous
Chicago fire. The light wood construction caught fire quickly. The earliest, most extensive example,
of prefabrication is Britain’s Great Exhibition of 1851, featuring a building called the Crystal Palace.
Designed by Sir Joseph Paxton in less than two weeks, the building used light and cheap materials:
iron, wood, and glass. The construction period lasted only a few months and consisted of assembling
the prefabricated components. After the exhibition, the palace was taken apart, piece by piece, and
moved to another location. Through the 1930s, the Aladdin “built in a day” house became common
in the United States, boasted by lower cost per foot in material due to its “ready cut” system that
maximized yield from standard lengths of timber. In 1932, a metal sandwich panel wall system was
developed, followed by George Fred Keck’s “House of Tomorrow” and the “Crystal House” for the
Chicago World’s Fair in 1933. The House of Tomorrow comprised a three-story with steel frame and
glass infill walls that resembled an airplane hangar, and the Crystal House improved the steel frame
concept. The House of Tomorrow was focused on cost effectiveness, passive heating, and modulation
of daylight. From 1954–1968, mobile homes, built as a module on a chassis in a factory, accounted
for 25% of all single family houses in the United States. The Hilton Palacio del Rio Hotel in San Antonio,
Texas, was built in 1968 for the Texas World’s Exposition of 1968 (still in use); it is a 500-room deluxe
hotel designed, completed, and occupied in 202 working days. Of the Palacio del Rio’s 21 stories, the
first four were built of conventional, reinforced concrete for support facilities. At the same time, an
elevator and utility core, also of reinforced concrete, were slip formed to a full height of 230 feet. From
the fifth floor to the 20th, 496 modules were stacked and connected by welding of steel embedment;
the 496 rooms were placed by crane in 46 days. In 1976, the building code was changed to distinguish
permanent homes as being those designed to the standard code (i.e., International Building Code (IBC))
and mobile homes to the HUD (U.S. Department of Housing and Urban Development) code. Up until
the 1990s, numerical control was restricted to those who could afford it; but today, small manufacturers
Sustainability 2016, 8, 558 4 of 16
and fabricators use Building Information Modeling (BIM) tools, Computer Numeric Control (CNC),
and 2-D laser cutting devices. This requires full scale modeling of components to effectively prove that
all elements fit together with appropriate tolerance [4,5,11,32,33].
2. Prefabricated Building Concepts
2.1. Degree of Prefabrication
Degree of prefabrication refers to the size and complexity of prefabricated components or
configuration of the final product. Decreasing the size of prefabricated components increases the
degree of on-site construction labor and vice versa. Prefabrication can be categorized into:
2.1.1. Components
Components allow for the greatest degree of customization and flexibility within the design
and execution phases, but they become numerous on construction sites and laborious to account for.
Componentized systems also require more joints and connections, and require more careful alignments
and infiltration checks. They are single fabricated elements such as stairs, gable ends, roof trusses (see
Figure 1), wall frames, wood kits, and precast concrete.
Sustainability 2016, 8, 558 4 of 16
2-D laser cutting devices. This requires full scale modeling of components to effectively prove that
all elements fit together with appropriate tolerance [4,5,11,32,33]
2.
2.1. Degree of Prefabrication
Degree of prefabrication refers to the size and complexity of prefabricated components or
configuration of the final product. Decreasing the size of prefabricated components increases the
degree of on-site construction labor and vice versa. Prefabrication can be categorized into:
2.1.1. Components
Components allow for the greatest degree of customization and flexibility within the design
and execution phases, but they become numerous on construction sites and laborious to account for.
Componentized systems also require more joints and connections, and require more careful
alignments and infiltration checks. They are single fabricated elements such as stairs, gable ends,
roof trusses (see Figure 1), wall frames, wood kits, and precast concrete.
(a)
(b)
Figure 1. Roof truss system: structural framework (a) and roof (b).
2.1.2. Panelized Structures
Panels are 2D planer elements used to build structural walls, floors, and roofs, alongside
columns. Panels enhance the speed and convenience of delivery of walls to a site. Included in this
category are structural insulated panels (SIPS), metal frame panels, and curtain walls (see Figure 2).
A typical example of panel system is the 30-story hotel near Dongting Lake in the Hunan Province of
China, that was built in 15 days [34].
(a) (b)
Figure 1. Roof truss system: structural framework (a) and roof (b).
Sustainability 2016, 8, 558 4 of 16
2-D laser cutting devices. This requires full scale modeling of components to effectively prove that
all elements fit together with appropriate tolerance [4,5,11,32,33]
2. Prefabricated Building Concepts
2.1. Degree of Prefabrication
Degree of prefabrication refers to the size and complexity of prefabricated components or
configuration of the final product. Decreasing the size of prefabricated components increases the
degree of on-site construction labor and vice versa. Prefabrication can be categorized into:
2.1.1. Components
Components allow for the greatest degree of customization and flexibility within the design
and execution phases, but they become numerous on construction sites and laborious to account for.
Componentized systems also require more joints and connections, and require more careful
alignments and infiltration checks. They are single fabricated elements such as stairs, gable ends,
roof trusses (see Figure 1), wall frames, wood kits, and precast concrete.
(a) (b)
Figure 1. Roof truss system: structural framework (a) and roof (b).
2.1.2. Panelized Structures
Panels are 2D planer elements used to build structural walls, floors, and roofs, alongside
columns. Panels enhance the speed and convenience of delivery of walls to a site. Included in this
category are structural insulated panels (SIPS), metal frame panels, and curtain walls (see Figure 2).
A typical example of panel system is the 30-story hotel near Dongting Lake in the Hunan Province of
China, that was built in 15 days [34].
(a) (b)
Figure 2. Customized curtain wall with glazing vision and building-integrated photovoltaic spandrel:
macrograph (a) and sectional view (b).
Sustainability 2016, 8, 558 5 of 16
2.1.2. Panelized Structures
Panels are 2D planer elements used to build structural walls, floors, and roofs, alongside columns.
Panels enhance the speed and convenience of delivery of walls to a site. Included in this category
are structural insulated panels (SIPS), metal frame panels, and curtain walls (see Figure 2). A typical
example of panel system is the 30-story hotel near Dongting Lake in the Hunan Province of China,
that was built in 15 days [34].
2.1.3. Modular Structures
Modules are made in complete 3D boxlike (volumetric) sections, multi section units, and stack-on
units (see Figure 3). Unlike in panelized or component levels of prefabrication, in modular construction
most of the interior and exterior finishes are put into place in the factory. They are up to 80–95 percent
complete when they leave the factory [4,35]. Modules are designed for ease of assembly. The size of a
module is a factor of module location in the building, manufacturing constraints, and transportation
limitations. It is worth mentioning that a category of prefab called a mobile home uses the modular
concept, but generally employs lighter construction and with a metal chassis as part of the floor
system; thus, as the name implies, it can be moved around quite often and easily. The air-tightness and
thermal performance of modular buildings can be much higher than previous prefab levels due to
tighter tolerances of joints [30]. A typical modular building is the Mini Sky City, a 57-story apartment
skyscraper constructed in 19 working days (previously described under Section 1.1) and the One9
modular building (will be described under Section 2.3).
Sustainability 2016, 8, 558 5 of 16
Figure 2. Customized curtain wall with glazing vision and building-integrated photovoltaic spandrel:
macrograph (a) and sectional view (b).
2.1.3. Modular Structures
Modules are made in complete 3D boxlike (volumetric) sections, multi section units, and
stack-on units (see Figure 3). Unlike in panelized or component levels of prefabrication, in modular
construction most of the interior and exterior finishes are put into place in the factory. They are up to
80–95 percent complete when they leave the factory [4,35]. Modules are designed for ease of
assembly. The size of a module is a factor of module location in the building, manufacturing
constraints, and transportation limitations. It is worth mentioning that a category of prefab called a
mobile home uses the modular concept, but generally employs lighter construction and with a metal
chassis as part of the floor system; thus, as the name implies, it can be moved around quite often and
easily. The air-tightness and thermal performance of modular buildings can be much higher than
previous prefab levels due to tighter tolerances of joints [30]. A typical modular building is the Mini
Sky City, a 57-story apartment skyscraper constructed in 19 working days (previously described
under Section 1.1) and the One9 modular building (will be described under Section 2.3).
Figure 3. Modular system.
2.1.4. Hybrid Structures
Hybrids usually combine panel and modular prefabrication systems to construct a whole
building. An example is the Meridian First Light House, depicted in Figure 4. The house is a net zero
energy dwelling designed to maximize energy drawn from the natural climate using a combination of
passive and active energy strategies. The house is made up of six independent prefabricated modules
and wooden decking surrounds the house linking the interior to the surrounding environment. The
building ranked third in the 2011 US Department of Energy’s Solar Decathlon [36–38].
(a)
Figure 3. Modular system.
2.1.4. Hybrid Structures
Hybrids usually combine panel and modular prefabrication systems to construct a whole building.
An example is the Meridian First Light House, depicted in Figure 4. The house is a net zero energy
dwelling designed to maximize energy drawn from the natural climate using a combination of
passive and active energy strategies. The house is made up of six independent prefabricated modules
and wooden decking surrounds the house linking the interior to the surrounding environment.
The building ranked third in the 2011 US Department of Energy’s Solar Decathlon [36–38].
Sustainability 2016, 8, 558 6 of 16
Sustainability 2016, 8, 558 5 of 16
Figure 2. Customized curtain wall with glazing vision and building-integrated photovoltaic spandrel:
macrograph (a) and sectional view (b).
2.1.3. Modular Structures
Modules are made in complete 3D boxlike (volumetric) sections, multi section units, and
stack-on units (see Figure 3). Unlike in panelized or component levels of prefabrication, in modular
construction most of the interior and exterior finishes are put into place in the factory. They are up to
80–95 percent complete when they leave the factory [4,35]. Modules are designed for ease of
assembly. The size of a module is a factor of module location in the building, manufacturing
constraints, and transportation limitations. It is worth mentioning that a category of prefab called a
mobile home uses the modular concept, but generally employs lighter construction and with a metal
chassis as part of the floor system; thus, as the name implies, it can be moved around quite often and
easily. The air-tightness and thermal performance of modular buildings can be much higher than
previous prefab levels due to tighter tolerances of joints [30]. A typical modular building is the Mini
Sky City, a 57-story apartment skyscraper constructed in 19 working days (previously described
under Section 1.1) and the One9 modular building (will be described under Section 2.3).
Figure 3. Modular system.
2.1.4. Hybrid Structures
Hybrids usually combine panel and modular prefabrication systems to construct a whole
building. An example is the Meridian First Light House, depicted in Figure 4. The house is a net zero
energy dwelling designed to maximize energy drawn from the natural climate using a combination of
passive and active energy strategies. The house is made up of six independent prefabricated modules
and wooden decking surrounds the house linking the interior to the surrounding environment. The
building ranked third in the 2011 US Department of Energy’s Solar Decathlon [36–38].
(a)
Sustainability 2016, 8, 558 6 of 16
Figure 4. Cont.
(b)
Figure 4. Hybrid structure–First Light House: completely installed building (a) and installation
procedure (b).
2.1.5. Unitized Whole Buildings
Whole buildings are standardized building units prefabricated to the highest degree of finish as
compared to components, panels, modules, and hybrids. More work is done under controlled
factory environment (with larger building structures), providing the opportunity for the
manufacturer to take control of quality and speed of the final product. However, sometimes their
bulk size and weight presents difficulties in transportation from the factory to the building site.
2.2. Load-Bearing Material Classification
Prefab can broadly be classified based on the type of load-bearing material. A plethora of
materials are employed for prefab purposes, however for load-bearing structures, steel, wood (for
small buildings), and precast concrete are generally used for their properties, availability, and cost.
A typical wooden structure prefab is the First Light House illustrated in Figure 4. The building was
inspired by the traditional Kiwi Bach (a New Zealand holiday home), designed with a strong
connection to the landscape. The buildings structural support and facades were wood-based. Wood
is natural, biodegradable, easy to machine, and a recyclable or reusable material [39]. For steel
structure prefab, a simple case is shown in Figure 3; a classic case would consist of a number of steel
modules (usually shipping containers) stacked on top of each other, such as the cantilevered
shipping container coffee shop in Johannesburg, South Africa [40]. Steel is known for its
strength-to-weight serviceability and durability. Unlike wood and steel, precast concrete are
generally used up to the panelized level of prefabrication because of weight constraints. For a
decade (i.e., 1985–1995), wooden structure, steel structure, and concrete structure prefab averaged
18%, 74%, and 8%, respectively, of the total prefabricated housing in Japan [41]. The trend may be
different today and plausibly change with the development of lightweight concrete that fulfills
strength requirements [42,43]. Moreover, due to its high compressive strength, precast concrete is
used as load-bearing stabilizing systems for high-rise modular prefab. For instance, 36 modules
were clustered around a precast concrete core (see Figure 5). Shifting away from conventional
concrete/cement clinker production towards energy-efficiency and CO2 emissions reduction,
high-activation grinding, oxygen-enriched combustion, the use of carbide slag and low lime
saturation factor, geopolymer cement, among others, have been proven to reduce the carbon
footprint of cement use [44]. Based on optimal mix designs, CO2 emissions of a low-carbon concrete
were reduced by 7% as compared to an actual mix design [45]; a potential 45% reduction in global
warming potential of concrete was also reported in [46] depending on mix proportions. Concrete
made with Portland cement, 35% fly ash (35% FA), and 80% blast furnace slag blended cements (80%
BFS) captured 47%, 41%, and 20% of CO2 emissions, respectively, during the life cycle of a 3 m high
building column with 30 × 30 cm2 cross-section. The blended cements emitted less CO2 per year
during the life cycle of the structure, although a high cement replacement reduced the service life
notably. For instance, the service life of blended cements with high amounts of blast furnace slag
Figure 4. Hybrid structure–First Light House: completely installed building (a) and installation
procedure (b).
2.1.5. Unitized Whole Buildings
Whole buildings are standardized building units prefabricated to the highest degree of finish as
compared to components, panels, modules, and hybrids. More work is done under controlled factory
environment (with larger building structures), providing the opportunity for the manufacturer to take
control of quality and speed of the final product. However, sometimes their bulk size and weight
presents difficulties in transportation from the factory to the building site.
2.2. Load-Bearing Material Classification
Prefab can broadly be classified based on the type of load-bearing material. A plethora of
materials are employed for prefab purposes, however for load-bearing structures, steel, wood (for
small buildings), and precast concrete are generally used for their properties, availability, and cost.
A typical wooden structure prefab is the First Light House illustrated in Figure 4. The building
was inspired by the traditional Kiwi Bach (a New Zealand holiday home), designed with a strong
connection to the landscape. The buildings structural support and facades were wood-based. Wood is
natural, biodegradable, easy to machine, and a recyclable or reusable material [39]. For steel structure
prefab, a simple case is shown in Figure 3; a classic case would consist of a number of steel modules
(usually shipping containers) stacked on top of each other, such as the cantilevered shipping container
coffee shop in Johannesburg, South Africa [40]. Steel is known for its strength-to-weight serviceability
and durability. Unlike wood and steel, precast concrete are generally used up to the panelized level
of prefabrication because of weight constraints. For a decade (i.e., 1985–1995), wooden structure,
steel structure, and concrete structure prefab averaged 18%, 74%, and 8%, respectively, of the total
prefabricated housing in Japan [41]. The trend may be different today and plausibly change with the
development of lightweight concrete that fulfills strength requirements [42,43]. Moreover, due to its
high compressive strength, precast concrete is used as load-bearing stabilizing systems for high-rise
Sustainability 2016, 8, 558 7 of 16
modular prefab. For instance, 36 modules were clustered around a precast concrete core (see Figure 5).
Shifting away from conventional concrete/cement clinker production towards energy-efficiency and
CO2 emissions reduction, high-activation grinding, oxygen-enriched combustion, the use of carbide
slag and low lime saturation factor, geopolymer cement, among others, have been proven to reduce
the carbon footprint of cement use [44]. Based on optimal mix designs, CO2 emissions of a low-carbon
concrete were reduced by 7% as compared to an actual mix design [45]; a potential 45% reduction
in global warming potential of concrete was also reported in [46] depending on mix proportions.
Concrete made with Portland cement, 35% fly ash (35% FA), and 80% blast furnace slag blended
cements (80% BFS) captured 47%, 41%, and 20% of CO2 emissions, respectively, during the life cycle of
a 3 m high building column with 30 ˆ 30 cm2 cross-section. The blended cements emitted less CO2 per
year during the life cycle of the structure, although a high cement replacement reduced the service
life notably. For instance, the service life of blended cements with high amounts of blast furnace slag
blended cement replacement was about 10% shorter, given the higher carbonation rate coefficient [47].
2.3. Prefab Methodology
2.3.1. General Approach
Some aspects of prefabricated construction are identical to conventional practices, such as site
preparation, excavation, and installation of the foundation. Simultaneously, detailed design and
offsite fabrication of building components, under controlled factory conditions, using the same
materials and designing to the same local building codes and standards as site-built facilities take place.
The prefab components are then delivered and assembled on-site to reflect the identical design intent
and specifications of the most sophisticated site-built facility, without compromise [48]. The ensuing
section features an example of on-site prefab assembly.
2.3.2. On-Site Assembly Case Study
One9, developed by the Moloney Group, is located at 19 Hall Street, just 7 km northwest of
Melbourne’s central business district in Moonee Ponds, a thriving hub of commercial, office, and
retail activity, bordered by quality residential dwellings and excellent lifestyle amenities. Designed
by the Amnon Weber architecture firm and constructed by Vaughan Constructions using Hickory
Group’s prefabricated building systems, One9 comprises 34, one- and two-bedroom contemporary
apartments over nine stories. The manufactured apartments were erected by Vaughan and Hickory
using 36 unitized building modules in just five days; the daily schedule and progress are shown in
Figure 5. Vaughan subcontracted Hickory to deliver the 36 modules, complete with the facades and
fully fitted with a combination of natural timber floors and high grade carpets, built-in wardrobes,
and full-length balconies. The nature of tall buildings is such that the modules are clustered around
a precast concrete core or stabilizing system; the modules are generally designed to resist vertical
loads and horizontal loads are transferred to the concrete core [30,49]. The Hickory manufactured
apartments offer light-filled and functional spaces for everyday living. Unique, modern design
highlights the capability of the modular technology to adapt to complex architectural concepts, and
features cantilevered terraces on all levels and clean framing on the front façade. One9 was completed
in November 2013 [50].
Sustainability 2016, 8, 558 8 of 16
Sustainability 2016, 8, 558 7 of 16
blended cement replacement was about 10% shorter, given the higher carbonation rate coefficient
[47].
2.3. Prefab Methodology
2.3.1. General Approach
Some aspects of prefabricated construction are identical to conventional practices, such as site
preparation, excavation, and installation of the foundation. Simultaneously, detailed design and
offsite fabrication of building components, under controlled factory conditions, using the same
materials and designing to the same local building codes and standards as site-built facilities take
place. The prefab components are then delivered and assembled on-site to reflect the identical
design intent and specifications of the most sophisticated site-built facility, without compromise
[48]. The ensuing section features an example of on-site prefab assembly.
2.3.2. On-Site Assembly Case Study
One9, developed by the Moloney Group, is located at 19 Hall Street, just 7 km northwest of
Melbourne’s central business district in Moonee Ponds, a thriving hub of commercial, office, and
retail activity, bordered by quality residential dwellings and excellent lifestyle amenities. Designed
by the Amnon Weber architecture firm and constructed by Vaughan Constructions using Hickory
Group’s prefabricated building systems, One9 comprises 34, one- and two-bedroom contemporary
apartments over nine stories. The manufactured apartments were erected by Vaughan and Hickory
using 36 unitized building modules in just five days; the daily schedule and progress are shown in
Figure 5. Vaughan subcontracted Hickory to deliver the 36 modules, complete with the facades and
fully fitted with a combination of natural timber floors and high grade carpets, built-in wardrobes,
and full-length balconies. The nature of tall buildings is such that the modules are clustered around a
precast concrete core or stabilizing system; the modules are generally designed to resist vertical
loads and horizontal loads are transferred to the concrete core [30,49]. The Hickory manufactured
apartments offer light-filled and functional spaces for everyday living. Unique, modern design
highlights the capability of the modular technology to adapt to complex architectural concepts, and
features cantilevered terraces on all levels and clean framing on the front façade. One9 was
completed in November 2013 [50].
Sustainability 2016, 8, 558 8 of 16
Figure 5. One9 modular building stabilized by a concrete core.
3.
3.1. Thermal Behavior
Hundreds of modular housing units were built as shelter after the 2008 Wenchuan earthquake,
in the Sichuan province of China. The prefab envelope was composed of 40 mm polystyrene foam
board sandwiched between two 0.5 mm stainless steel layers. In situ measurement of the prefab
houses showed that indoor air temperature reached 30 °C, while inner surface temperature could
escalate to 55 °C. Solar heat gain affected the indoor thermal environment significantly. The prefab
envelope was found to be of low thermal resistance and thermal inertia; occupants complained of
the poor indoor thermal environment [51,52]. To limit solar radiation heat gain, a model of the
prefab housing units was fabricated with a 1 mm retro-reflective material integrated as the
outermost layer of the prefab building envelope. The thermal behavior of the prefab with and
without retro-reflective material was studied considering peak summer days and contrasted. The
reflectivity of the retro-reflective material was 0.543.
The maximum outdoor air temperature difference was up to 10 °C in the daytime, and solar
radiation peaked at 850 W/m2 around 14:00 during the day. Generally, the indoor air temperature of
the modular housing unit without retro-reflective material (Model 1) and modular housing unit with
retro-reflective material (Model 2) fluctuated nearly in sync with the outdoor air temperature due to
the low thermal resistance and the small thermal inertia of ultrathin envelope. It was observed that
the indoor air temperature for Models 1 and 2 was almost the same with the outdoor air temperature
on the first day, when the total horizontal radiation was generally low, due to cloud overcast.
However, the indoor air temperature for Models 1 and 2 was higher than the outdoor air
temperature when the total horizontal radiation was high. Additionally, it was deduced that the
peak air temperature of Model 2, compared to Model 1, reduced by 7.1 °C for the second day and 7.4
°C for the fourth day [51]. Furthermore, at the microclimate scale, the use of reflective material could
contribute to reducing the ambient air temperature due to the heat island effect [53]. However,
unless the retro-reflective material is removable, this approach is only suitable during the summer,
when the sun is high and incident total horizontal radiation would be high. Alternatively, a phase
change material (PCM) used in passive latent heat thermal energy storage can control the
temperature fluctuations of both winter and summer [54]. Two models of the prefab housing units
were fabricated; Model 1 was a similar replica of the modular housing units in Wenchuan, while
Model 2 had an exterior layer of PCM. The phase transition temperature range, latent heat, specific
heat capacity, density, and thermal conductivity of the PCM were 18 °C–26 °C, 178.5 kJ/kg, 1785
J/kgK, 1300 kg/m3, and 0.25–0.5 W/mK (depending on the phase state), respectively. The theoretically
calculated thermal resistance and thermal inertia index of Models 1 and 2 were 1.282 (m2K/W) and
1.374 (m2K/W), 0.783 and 1.916, respectively [55]. Based on a validated simulation model with less
than 5% error, Table 1 shows the results for Models 1 and 2 for different climatic zones in China.
Figure 5. One9 modular building stabilized by a concrete core.
3. Performance of Modular Prefab Cases
3.1. Thermal Behavior
Hundreds of modular housing units were built as shelter after the 2008 Wenchuan earthquake,
in the Sichuan province of China. The prefab envelope was composed of 40 mm polystyrene foam
board sandwiched between two 0.5 mm stainless steel layers. In situ measurement of the prefab houses
showed that indoor air temperature reached 30 ˝C, while inner surface temperature could escalate
to 55 ˝C. Solar heat gain affected the indoor thermal environment significantly. The prefab envelope
was found to be of low thermal resistance and thermal inertia; occupants complained of the poor
indoor thermal environment [51,52]. To limit solar radiation heat gain, a model of the prefab housing
units was fabricated with a 1 mm retro-reflective material integrated as the outermost layer of the
prefab building envelope. The thermal behavior of the prefab with and without retro-reflective material
was studied considering peak summer days and contrasted. The reflectivity of the retro-reflective
material was 0.543.
The maximum outdoor air temperature difference was up to 10 ˝C in the daytime, and solar
radiation peaked at 850 W/m2 around 14:00 during the day. Generally, the indoor air temperature of
the modular housing unit without retro-reflective material (Model 1) and modular housing unit with
retro-reflective material (Model 2) fluctuated nearly in sync with the outdoor air temperature due to
the low thermal resistance and the small thermal inertia of ultrathin envelope. It was observed that the
indoor air temperature for Models 1 and 2 was almost the same with the outdoor air temperature on
the first day, when the total horizontal radiation was generally low, due to cloud overcast. However,
the indoor air temperature for Models 1 and 2 was higher than the outdoor air temperature when the
total horizontal radiation was high. Additionally, it was deduced that the peak air temperature of
Model 2, compared to Model 1, reduced by 7.1 ˝C for the second day and 7.4 ˝C for the fourth day [51].
Sustainability 2016, 8, 558 9 of 16
Furthermore, at the microclimate scale, the use of reflective material could contribute to reducing
the ambient air temperature due to the heat island effect [53]. However, unless the retro-reflective
material is removable, this approach is only suitable during the summer, when the sun is high and
incident total horizontal radiation would be high. Alternatively, a phase change material (PCM) used in
passive latent heat thermal energy storage can control the temperature fluctuations of both winter and
summer [54]. Two models of the prefab housing units were fabricated; Model 1 was a similar replica
of the modular housing units in Wenchuan, while Model 2 had an exterior layer of PCM. The phase
transition temperature range, latent heat, specific heat capacity, density, and thermal conductivity of
the PCM were 18 ˝C–26 ˝C, 178.5 kJ/kg, 1785 J/kgK, 1300 kg/m3, and 0.25–0.5 W/mK (depending on
the phase state), respectively. The theoretically calculated thermal resistance and thermal inertia index
of Models 1 and 2 were 1.282 (m2K/W) and 1.374 (m2K/W), 0.783 and 1.916, respectively [55]. Based
on a validated simulation model with less than 5% error, Table 1 shows the results for Models 1 and 2
for different climatic zones in China.
Table 1. Temperature fluctuations based on climatic conditions [55].
Climate Zone City Season Tout Tin 1 Tin 2 ∆Tday ∆Tnight
Severe cold Harbin
Winter ´25.1–11.0 ´26.9–11.0 ´18.7–14.7 5.7 8.7
Transition 13.2–24.2 12.4–32.3 22–25.2 7.7 10.0
Summer 14.4–28.4 14.8–35.9 25.0–29.5 7.4 9.9
Cold Beijing
Winter ´7.3–8.4 ´8.3–15.4 ´0.5–5.1 11.5 8.4
Transition 11.8–29.4 11.9–38.5 24.2–29.6 9.7 13.9
Summer 27.2–34.8 27.2–42.0 33.6–37.4 4.9 7.5
Hot summer
and cold
winter
Shanghai
Winter 0.9–14.9 0.5–21.6 7.7–12.6 9.8 7.4
Transition 17.4–20.7 16.2–27.6 23.7–25.3 2.7 8.1
Summer 27.2–32.8 26.1–41.3 31.5–36.6 7.3 6.7
Hot summer
and hot
winter
Guangzhou
Winter 6.0–14.9 4.4–31.5 15.4–21.18 11.0 11.6
Transition 13.8–25.8 12.7–36.3 22.1–27.9 9.7 9.8
Summer 27.1–35.6 27.1–43.6 35.4–38.8 5.2 9.4
Temperate Kunming
Winter 1.9–17.8 1.7–28.6 12.5–18.5 11.2 11.6
Transition 13.3–23.7 12.0–32.5 21.2–25.3 8.1 9.8
Summer 13.9–25.8 13.8–36.1 24.4–36.1 7.7 10.3
Where Tout is the outdoor air temperature, Tin1 is the indoor air temperature of Model 1, Tin2
is the indoor air temperature of Model 2, ∆Tday is the maximum temperature difference between
Models 1 and 2 during daytime, and ∆Tnight is the maximum temperature difference between Models 1
and 2 at night. Generally, the indoor air temperature fluctuations of Model 2 were smaller than those
of Model 1. This was attributed to the PCM’s heat storage performance. That is, the total attenuation
degree of the wall-integrated PCM was 32.233 compared with a total delay time of 3.705 h; which is
nearly 3 h longer than the wall without PCM. Furthermore, the indoor air temperature fluctuations
in Model 1 for the five cities were higher than 10 ˝C, while the maximum indoor air temperature
fluctuations in Model 2 was only 5.8 ˝C. For instance, in Beijing where the outdoor air temperature
difference is the largest, the indoor air temperature difference of the two models was up to 13.9 ˝C at
night and 9.7 ˝C during the day, in winter [55].
3.2. Acoustic Constraints
Consumers favor multi-unit dwellings in Korea. Weight impact sounds generally occur in
multi-unit dwellings and are often caused by young children running or jumping. Such sounds
are irregular noise that is unpleasant for the person living in the floor below. Based on computer
simulations and mock-up models, the characteristics of vibration in floor structure and floor impact
sound applicable for apartment houses with common modular structure were studied in [48].
It was found that the flooring with double concrete slabs had the highest performance in reducing
heavyweight impact sounds. The use of mortar for insulation increased the vibration reduction effect.
Heavyweight impact sound was affected significantly by the load on the flooring structure, whereas
for lightweight impact sound the performance was higher with dry construction insulation structures
Sustainability 2016, 8, 558 10 of 16
compared to wet construction structures. Lightweight impact sound was caused by less impact on the
floor, which could be why dry insulation construction had a better ability to absorb smaller vibrations.
3.3. Seismic Resistance
Modular steel buildings (MSBs) are being used increasingly for two- to six-story schools,
apartments, dormitories, hotels, and in similar buildings where repetitive units are required.
The lateral resistance of this unique building type is often achieved by adding diagonal braces [56–58].
In MSBs, modular units made of high strength and durable steel sections are built and finished under
a controlled manufacturing environment and connected horizontally and vertically. Lateral loading on
each floor is transferred through the horizontal connections (HC) to the modular-braced frame and
then through the vertical connections (VC) to the foundation.
The following features specifically distinguish the MSB-braced frame from a regular steel-braced
frame: (1) the existence of ceiling beams (CB) and ceiling stringers (CS) in the MSB frame system;
(2) the floor beams (FB) may be set directly above the ceiling beams (CB) without mechanical
connections, except at column locations; (3) the brace members in a typical modular steel frame do not
intersect at a single working point which may lead to high seismic demands on the vertical connection
(VC) between different units/modules; (4) the horizontal connections (HC) of separately-finished
modules, shown in section A-A, are achieved by field-bolting of clip angles which are shop-welded
to the floor beams; (5) the vertical connection (VC) between modular units, shown in section B-B,
typically involves partial welding of the columns of a lower and an upper modules which may lead to
independent upper and lower rotations at the same joint [59]. An experimental testing under repeated
cyclic loading involved specimen of a one story MSB braced panel extracted and scaled from a typical
four-story modular building frame.
The MSB structure showed stable ductile behavior up to very high drift levels; there was no
significant strength and stiffness degradation with cycling and showed superior energy dissipation
per cycle in each of the load steps. Seismic performance of a framed structure can be measured by its
energy dissipation characteristics.
3.4. Energy Consumption
The existing building stock consumes a momentous quota of the total primary energy in many
countries [60,61]. Additionally, many of the buildings that will exist in 2050 are the ones that exist
today; thus, it is logical to focus on minimizing this energy demand. The refurbishment of the existing
buildings has a fundamental role to meet stringent building standard requirements such as the recast
Energy Performance of Buildings Directive within the European Union (EPBD 2010/31/EU) [62];
and without any doubt their great numerical superiority in relation to the new buildings represents
an opportunity for achieving overall goals for energy savings and reduction of CO2 emissions level
globally. By combining modular construction with passive house standard, a modular passive house
dorm that drastically reduced energy consumption was built. The building’s heating and cooling was
about $350/month as compared to $1200–$1400/month for a similar building according to use and
floor area [63].
3.5. Life Cycle Analysis
Energy and materials are used, and corresponding environmental impacts incurred in large
quantities throughout the life cycle of a building. While the occupancy phase of a building has been
reported to account for about 70%–98% of a building’s energy use, the construction phase has been
found to account for about 2%–26%, depending on the reference building’s design and intended
use [64–69]. A survey of modular construction facilities revealed that practically all building materials
were reused, with the exception of some gypsum (3.4–3.9 kg/m2) and copper wire (0.15–0.48 kg/m2),
which are impractical to use in small sections. The life cycle analysis (LCA) for greenhouse gas
(GHG) emissions considering materials production, transportation, and construction phases only for
Sustainability 2016, 8, 558 11 of 16
three modular and five on-site companies was investigated in [32], considering materials production,
transport, and construction phases of the building life cycle. Mod1, Mod2, and Mod3 are LCA
results based on data of modular construction companies, while Conv1, Conv2, Conv3, Conv4, and
Conv5 are LCA results calibrated using data of on-site construction companies. Most data were
reported as amount per week or year; thus, the authors scaled down annual production estimates
of the construction companies to a common functional unit of 186 m2; a two-story home model.
The analysis showed that impacts from modular construction were, on average, lower than those
from on-site construction, but that there were significant variations within each. For instance, in
the case of Mod1, the company’s emissions were significantly higher than the other two modular
cases, and also higher than one of the five on-site companies. This particular facility was located
in a rural area with a commute that is more than twice as long as for the other modular facilities,
when normalized for production volumes. This factory also reported higher levels of electricity use
than the others and was heating with fuel oil, again leading to increased levels of emissions. Energy
use on-site and worker transport to the site were the most important categories for GHG emissions
from conventional construction, which is intuitive as both represent direct combustion of fossil fuels.
Therefore, reducing unnecessary worker trips, idling of equipment, and temporary heating through
effective management practices remain the most important goals of low-carbon construction of homes.
For example, Conv2 homes had low impacts relative to the set of conventional homes. In this particular
case, the contractor worked with a local crew and so reported relatively short distances for worker
transport to the construction site. This contractor also reported lower consumption of all fuels and
electricity on-site than reported by other contractors. On average, GHG emissions from conventional
construction were about 40% higher than for modular construction [32]. That said, depending on
a reference building’s design and use, the maintenance or occupancy, demolishing and rebuilding
have large impacts in terms of embodied energy and LCA [67–70]; nonetheless, in [32] the authors
did not consider whole cradle-to-grave LCA, the results could be different should other stages and
environmental impacts been factored into the LCA. Over a 50 year life span LCA of modular and
conventional housing (floor area of 135 m2 in each case), it was found that the conventional home
produced 2.5 times more construction waste than the modular home; additionally, the latter had 5%
less total life cycle energy consumption and 5% less global warming potential than the former due to
higher air tightness, although the study simplified assumptions [71].
4. Future Pathways
Prefabrication is a promising strategy to realize lean construction. Nowadays, prefabricated
buildings are more focused on harmonization of various systems, minimizing thermal bridges,
material efficiency, automation and optimization of production, time efficiency, and mass customization
potentials, as compared to the earliest prefabricated buildings, which were more focused on satisfying
a need for a booming housing demand within a short time limit. Among the various degrees
of prefabrication, modular buildings maximize the most gain in time savings, because they are
prefabricated to a greater degree of finish. Modular buildings are constructed based on local building
codes and standards, in the same way as on-site built construction; thus, of equal quality to an on-site
built construction. The materials and building envelope U-value requirements for both modular
and on-site built construction are exactly the same for the same building use, with the exception of
added structure to ensure that the modular building can be transported to the site without being
damaged. Over the years, modular buildings have been designed astutely and constructed in such
a manner that sometimes, it is impossible to tell the difference between a modular building and a
conventional building. However, modular buildings are just not limited to design, manufacturing, and
construction stages, but also maintenance during occupancy, deconstruction, and recycle or reuse [72].
Thus, similar to other industrialized products that usually bears a date of expiry or terms of use, a
product lifecycle management or monitoring concepts needs to be implemented in modular buildings.
Limited information and real-time data of modular buildings, covering all stages of the prefab has
Sustainability 2016, 8, 558 12 of 16
hampered a comprehensive cradle-to-grave LCA. In countries like Japan where modular buildings
are advanced and hold a considerable market share, energy monitoring systems are often installed.
Owners can choose to install photovoltaics for energy generation; this, of course, comes with an extra
cost. In particular, the lack of uniform definition for various levels of prefabrication, and contextual
differences surrounding mobile or manufactured homes and modular buildings, has contributed
to misunderstandings of the technology [73]. Often confused with mobile or manufactured homes,
modular buildings are built to IBC code, without chassis, and are set on-site permanently. The mass
public needs to be educated on the clear difference between the two. Local building codes are often
adopted for modular buildings; this hampers performance comparison of modular buildings with
different geographic locations. A universally-binding standard for modular buildings, that factors
geographic location, is clearly needed. Although often pricy, integrative 3D modeling software and
project management software, which enable prompt sharing of designs, information, and results,
are crucial to the success of prefab; more so are multi-objective algorithms that use mathematical
approaches to solve real-time challenges [74], such as artificial neural networks used to predict the
energy use of buildings [75]. Numerous projects incorporating prefab (on various levels) have already
been completed successfully, and many more are planned. For instance, a 100-story tower using
unitized system has been granted permit to be constructed in Melbourne; completion is due in 2019.
Additionally, Chinese constructors have proposed a 220-story 838 m vertical city using modules;
if permit is granted, it would become the world’s tallest building. The potential for growth in the
building economy; embracing greater productivity, total sustainability, improving workplace and
workforce safety, was theoretical some ages ago, but is a practical realization today and hereafter,
through prefab.
5. Summary and Outlook
The building industry is refabricating architecture through prefabrication. Similar to the
automobile, shipbuilding, and aerospace industries, the construction industry aims to deliver
an integrated prefab architecture that meets design requirements according to budget, quality
specifications, as well as being on time. Using a case study based methodology, this study was
designed to review the classification and actual performance of assorted prefabricated architecture.
The earliest prefabricated buildings date back to the early seventeenth century, when houses were
fabricated in England and shipped abroad. From literature, there are numerous benefits that can be
realized by adopting prefabrication; notably, material and time efficiency, as well as reduced impacts
of construction on the environment. Some authors have described prefabricated architecture on the
modular scale as a sustainable approach. Nonetheless, there are some hindrances to prefabrication;
notably, transportation restrictions due to module size and weight, high level of project coordination,
negative market perception, and lack of general knowledge on prefab. Contrary to the general
perception, designing with prefab components is not a barrier to creativity; rather, by standardizing
typical prefab components and providing mass customization options, final costs are lowered through
economies of high-volume work. The building envelope of prefabricated architecture should be tailored
to suit local climatic conditions and building codes to ensure a comfortable indoor environment. On
average, greenhouse gas emissions from conventional construction were higher than for modular
construction. Measuring seismic performance of a modular steel brace frame structure by energy
dissipation characteristics showed that the structure was stable and behaved in a ductile manner up
to very high drift levels; there was no significant strength and stiffness degradation with cycling and
showed superior energy dissipation per cycle in each of the load steps. For better implementation
of prefabrication, early design stage should be considered and included in the construction methods.
For the future, there is need to improve assurance of stakeholders by making known to the public
performance data of existing prefabricated architecture; only then can prefabricated and conventional
architecture be juxtaposed and quantified. Further, reducing costs through mass customization,
promotions, and policies will be an important factor to widen the commercialization of prefab.
Sustainability 2016, 8, 558 13 of 16
Acknowledgments: This work was supported by the Human Resources Development (No. 20134010200540) and
the International Cooperation (No. 20148520011270) of the Korea Institute of Energy Technology Evaluation and
Planning (KETEP) grant funded by the Korea Government Ministry of Trade, Industry and Energy.
Author Contributions: This paper was a collaborative effort by all the authors. The authors contributed to
different aspects of the research methodology and development, literature review, discussion and analyses.
Conflicts of Interest: The authors declare no conflict of interest.
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© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
http://dx.doi.org/10.1016/0360-1323(96)00017-0
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http://creativecommons.org/licenses/by/4.0/
- Introduction
- Future Pathways
- Summary and Outlook
Background
Brief History of Prefab
Prefabricated Building Concepts
Degree of Prefabrication
Components
Panelized Structures
Modular Structures
Hybrid Structures
Unitized Whole Buildings
Load-Bearing Material Classification
Prefab Methodology
General Approach
On-Site Assembly Case Study
Performance of Modular Prefab Cases
Thermal Behavior
Acoustic Constraints
Seismic Resistance
Energy Consumption
Life Cycle Analysis
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Implementation of Building Information Modeling
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Challenges
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Implementation of Building Information Modeling (BIM)
in Modular Construction: Benefits and Challenges
Na Lu1 and Thomas Korman2
1. Assistant Professor, Department of Construction Management and Engineering
Technology, University of North Carolina at Charlotte, Charlotte, NC, USA (704)
687-2718, Email: na.lu@uncc.edu
2. Assistant Professor, Construction Management Department, California State
University, San Luis Obispo, CA, USA (805)756-5612, Email:
tkorman@calpoly.edu
Modular Construction consists of one or more structure units fabricated in a
manufacturing plant away from the jobsite. In the building industry, prefabricated
modules are normally completed with trim work, electrical, mechanical and plumbing
installed. Previous studies have proved that Modular Construction provided many
advantages to the built environment, including the reduction of need for workforce,
the reduction of onsite Green House Gas (GHG) emissions, and the improvement of
construction schedule and product quality; however the extensive demand of pre-
project planning and coordination among members of cross-interdisciplinary
professionals have significantly impeded the application of this technique. With the
recent development of Building Information Modeling (BIM), these challenges could
be overcome through the BIM platform. Through case studies the benefits and
challenges of implementing BIM in modular construction are clearly identified.
Keywords: Building Information Modeling, Coordination, Prefabrication,
Building Systems.
Introduction
Modular construction refers to factory-built building units completely assembled or
fabricated in a manufacturing plant away from the jobsite, then transported and
assembled on site (Pasquire, 2002). Modular building normally consists of multiple
rooms with three-dimensional units, which are constructed and pre-assembled
complete with trim work, mechanical, electrical and plumbing components installed
(O’Brien, 2000). A large portion of construction research conducted in the United
States and globally discusses that the use of modular construction provides many
significant advantages, including: 1) the reduction of overall project schedules, 2) the
improvement of product quality, 3) increased onsite safety performance, 4) a
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reduction in the need for onsite skilled workers, and 5) a decrease in the negative
environmental impact caused by construction operations (Gann, 1996; Hsieh, 1997;
Edge, 2002; Gibb, 2001; Venables, 2004; Lu, 2007). However, the coordination and
fabrication of the Mechanical, Electrical and Plumbing (MEP) systems in modular
construction has always being one of the most challenging tasks encountered in the
delivery process of modular constructions (Tatum, 2000; Korman, 2001; Lu, 2008).
The MEP coordination and fabrication process involves defining the locations for
components of building systems, in where are often congested spaces, to avoid
interferences and to comply with diverse design and operations criteria. There are
three primary reasons contributing to the challenges of MEP fabrication in modular
construction. First, the process is highly fragmented between design and construction
firms. Second, the level of technology used in different coordination scenarios has
historically varied significantly between engineers and construction contractors.
Third, historically the process did not provide a model for use by specialty contractors
plan prefabrication (Korman, 2001).
Using Building Information Modeling (BIM) to coordinate, document and fabricate
MEP systems in modular constructions appears to be an effective approach to
overcome these challenges. In 2009, Maine based Modular Construction Company
KBS has successfully delivered their recently awarded modular project by integrating
BIM technology into the design and construction process for the New Street Project,
Cambridge, MA, as presented in Figure 1 (KBS, 2009).
(a) Architecture BIM Model to present modular wall details
(b) Installation prefabricated Roofs (c) Prefabricated Wall Panels
Figure 1: BIM application in Modular Construction Projects (Tocci & KBS)
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BIM Background and Applications
BIM is commonly defined as the process of creating an intelligent and computable
three-dimensional (3D) data set and sharing the data among the various types of
professionals within the design and construction team. With BIM technology, an
accurate virtual model of a building is constructed with precise geometry and relevant
data needed to support the procurement, fabrication, on-site installation activities, as
presented in Figure 2 (Eastman et al, 2008).
(a) Structural Steel BIM Model (b) Automatic Quantity Takeoff from BIM Model
Figure 2 BIM Model Applications in Cost Engineering
(Courtesy of: Holder Construction Co, Atlanta, Georgia, USA)
The use of BIM technology allows for the creation of intelligent contextual semantic
digital models in terms of building elements and systems, such as spaces, walls,
beams, columns and MEP systems, whereas 3D CAD technology is limited to
generating drawings in graphical entities in terms of lines, arcs and circles. In addition,
BIM technology allows for a creation of a model that contains information related to
the building physical, functional and procurement information. For instance, the BIM
model would contain data about the geometry, location, its supplier, operation and
maintenance schedule, flow rates, and clearance requirements for an air-handling unit
(CRC Construction Innovation, 2007).
Using BIM technology allows designers, engineers, and construction contractors to
visualize the entire scope of a building project in three dimensions. Therefore, BIM
technology is not only defined by simply creating a 3-D data set for internal analysis.
When most professionals refer to a 3-D model today, they are only referring to a
digital 3-D data set that contains geographical representations of objects placed in
relation to each other. BIM technology is also known as the process of using a 3-D
model and associated data set to improve collaboration among project participants.
Using this collaborative approach, designers and builders can plan, in precise detail,
the location and clearances required for a complete and successful project.
The implementation of BIM systems in modular construction normally involves in the
following process:
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Visualization: ability to create a 3D presentation of building modules
geometry, location, space, contained systems in relation to each other
Modeling: ability to generate a 3D rendering tool to present the final product
and finishes to owners, designers and constructors
Code reviews: allows for building officials and fire officials could use the 3D
models with related data for code compliance reviews
Fabrication/ shop drawings: facilitates for the generation of detailed shop
drawings could be easily produced once the BIM model is completed
Communication: facilitates simultaneously creation of construction documents,
product imagery, rapid prototypes, exterior envelope, interior finishing, and
MEP fixtures of building modules. Through this single information platform,
BIM promote collaborations among the design team, consultant, constructors
and the clients
Cost estimating: provides for cost estimating, material quantifications, and
pricing to be automatically generated and modified while changes are applied
for each building module
Construction sequences: provides a complete construction schedule for
material ordering, fabrication, delivery and onsite installation of each building
systems. With the integration of 3D rendering, 4 D (3D model + scheduling
information) could be easily generated during the project design and
construction phase
Conflict, interference and collision detection: ability to determine building
system interferences which can be visually presented. For instance, an air
distribution duct for the HVAC system physically interfering with a concrete
beam
Today, there are many examples of BIM software. NavisWorksTM is a software
program that interprets all of the other software programs used by various specialty
contractors and design engineers. NavisWorksTM is to software what the Rosetta Stone
was to interpreting languages. This software has the potential to unlock and or
interpret the other 2-D CAD drawings. This program only identifies the clashes and
the individual specialty contractors need to revisit their own software programs and
revise them in order to resubmit. NavisWorksTM will then reanalyze the new shop
drawings and hopefully there are fewer or no clashes. Obviously, when there are
multiple specialty contractors involved in a project, the challenge is to create an
environment whereby everyone has worked out the details successfully.
There are many3-D graphical representation software programs available for architects
and engineers to model their project in BIM platform as well. Graphisoft’s
ArchiCADTM allows one to draw in 3-D or import a 2-D drawing and create a 3-D
model. This program allows you to toggle back and forth from 2-D to 3-D with the
click of a mouse. AutoDeskTM is a 2-D drafting program coupled with RevitTM
creating the 3-D model.
MEP Coordination in Modular Construction prior to BIM technology
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Without the use of BIM system MEP coordination, prefabrication phase in modular
construction begins after the design and preliminary routing of all building systems
(mechanical, plumbing, electrical, etc.) is complete. The design is considered complete
when engineers have sized all components (e.g., HVAC duct, pipe, conduits),
completed the engineering calculations, and produced the diagrammatic drawings.
Representatives from each of the specialty contractors (primarily HVAC wet and dry,
plumbing, electrical, and fire protection) meet to discuss their particular designs and
drawings, which indicate the proposed routing for each system to follow to service
each required location. Most specialty contractors refer to these contract drawings as
schematic design drawings. The engineers’ stamp that the engineer provides only
insures that the design of the systems will work functionally. It does not ensure that
the system will actually fit within building.
In this scenario, the design consultant remains the engineer of record (EOR) and
retains liability for the system functionality; however, these drawings are not detailed
enough to either fabricate components or construct the systems. The required size of
components, such as conductor wire, duct dimensions, and pipe diameter are called
out on the drawings, but no scaling of the components is shown in the drawings. It is
the specialty contractor’s responsibility to build the particular building system from
these design documents. This requires that the contractor produce shop drawings, also
known as fabrication drawings. The shop drawings include the detailed information
required by the specialty contractor to fabricate and install a particular building
system.
During coordination meetings, the participating specialty contractors compare
preliminary routing for their systems to identify and resolve conflicts. The MEP trades
use a sequential comparison overlay process to compare their design drawings until
they resolve all interferences. This often requires preparing section views for highly
congested areas to identify interferences. The preliminary shop drawings that each
specialty contractor brings to the meeting indicate the path preferred for each branch
of the system to reach the required locations and perform essential functions.
Architectural, structural, and diagrammatic drawings constrain this routing. Within
these constraints, specialty contractors route systems based on the lowest cost;
however, they generally do not consider the other systems. They also decide which
specialty contractor(s) will revise their design and submit requests for information
regarding problems that require an engineering resolution. The product of this process
is a set of coordinated shop drawings that the specialty contractors submit to the
design engineer for approval that the system functionality has not been compromised.
Using BIM for MEP Coordination in Modular Construction
Historically, there has been a wide variation in the level of technology used in the
MEP coordination process. At the low-tech end of the spectrum, specialty contractors
drafted plan-views on translucent media and prepare section-views when necessary. At
the other extreme, progressive contractors have used 3D CAD to improve the process.
With the recent development of BIM, the process has gravitated toward the use of
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BIM software.
There are many locations in buildings that repeatedly cause coordination problems.
These include building corridors, points of entry and exit, openings in shear walls, and
vertical utility chases. Reserving space for access is more easily accomplished using
BIM models. However, often times resolving interferences most frequently entails
determining which building system has priority. In these cases priority is typically
determined by evaluating the functionality of each system. In the event of
interferences or clashes, the newly proposed route must be evaluated to determine if
the new route changes the systems’ functionality. If it is determined that the new route
affects the functionality of the system performance, it is given priority over another
system.
The need for MEP coordination grows out of the lack of detailed design provided for
fabrication and installation of building systems, and exists regard-less of the project
delivery process used. The current conditions in the design and construction industry
drive current practice for MEP coordination. The use of BIM technology has created
an opportunity to improve the current process by changing the way design engineers
and construction contractors interact with each other during the coordination process.
BIM offers parties involved in MEP coordination to take the opportunity to align goals
and define requirements during the construction of the model. In addition, when
historically MEP design consultants have not considered constructability issues and
made assumptions about constructability or ignore the issue totally, the use of BIM
allows a mechanism for dialogue between specialty contractors who install the system
and design engineers who design the system.
Benefits and Challenges of BIM Implementation: Case Studies
The following case studies document the implementation of BIM in two different
types of commercial projects. Specific examples of using BIM facilitating MEP
coordination in Modular Construction are discussed as well. The project and owners
name are anonymous for confidentiality purpose. The construction manager was
Rogers Builders, headquartered at Charlotte, NC. The company has over 350
associates and nationally ranked among Top 100 CM-at-Risk firm by Engineering
News Record (ENR) and Top 10 Healthcare General Contractors by Modern
Healthcare for the last 10 Consecutive years. The company has implemented BIM
system for every project they have built since 2007, with no premium cost to the
owner side. Rogers Builders maintain that the cost for development and maintenance
of BIM model with in-house resources is controlled at 0.1% of total project cost.
Case Study 1: Healthcare Expansion Project, Charlotte, North Carolina, USA
Project Scope: $44Million, 110,000 SF healthcare expansion project
Modular Construction: prefabricated concrete panels are used for floor slab
Delivery Methods: CM @ Risk
Contract Type: Cost Plus with Guaranteed Maximum Price
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Design Assistant: No Design Involvement
BIM Implementation Cost: $44000
BIM Implementation Saving: $220,000
BIM Platform: NavisworkTM
(a) Structural BIM Model (b) Architecture BIM Model (C) MEP BIM Model
Figure 3 BIM Models in Healthcare Expansion Project
(Courtesy of: Rogers Builders, Charlotte, NC, USA)
For this project, the BIM model produced architecture, structural systems and MEP
systems. It was developed to provide a dynamic platform for inter-disciplinary
collaborations as presented in Figure 3. Through the entire project management phase,
Roger Builders used the BIM models for cost engineering, subcontractor buyout, MEP
coordination and clash detection. The specific benefits have been identified by using
BIM model in this project includes:
Clearly defined subcontractor’s work scope
Automatic quantity extraction of structural steel and major MEP systems
Facilitate shop drawing of structural steel and MEP systems
560 clash conflicts between MEP systems and the structural systems were
identified prior to the fabrication of the MEP and structural systems
Case Study 2: High School Project, Gastonia, North Carolina, US
Project Scope: $38 Million, 220,000 SF High School Project
Modular Construction: Prefabricated classroom with rough-in MEP installation
Delivery Methods: Design- Build
Contract Type: Cost Plus with Guaranteed Maximum Price
Design Assistant: Extensive Design Involvement
BIM Implementation Cost: $38000
BIM Implementation Saving: N/A
BIM Platform: NavisworkTM
A comprehensive BIM model with overlapped architecture, structural, MEP model has
been created by Rogers Builders BIM specialists at the design phase of the project, as
presented in Figure 4.The BIM model was used extensively for design coordination,
subcontractor work scope clarifications, cost engineering, MEP coordination and
project sequencing.
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(a) 1st Floor BIM Model (b) 2nd Floor BIM Model
Figure 4 High School B Project BIM Model
(Courtesy of: Rogers Builders, Charlotte, NC, USA)
All MEP coordination was conducted through the BIM platform. It is very beneficial
to have fully integrated architecture, structural systems, and MEP systems in single 3D
file, which reduces change for human error and provides a visual check for
interferences for clash detections. By using the BIM model for this project, 258
conflicts were identified and eliminated during the design phase, as presented in
Figure 5 and Figure 6. Each classroom module was accurately manufactured offsite
with rough-in plumbing pipes and electrical conduits installed. The finishing MEP and
furnishing process began after the installation of each classroom module.
Figure 5 Ductwork Conflicts Structural Steels Figure 6 Ductwork conflicts with Bar Joists
(Picture Courtesy: Rogers Builders, Charlotte, NC, USA)
Through these case studies, the researchers identified that the most effective use of
BIM models was for design coordination, walk-through animation and clash
detections. This was more so for modular construction project which requires
extensive design coordination especially for MEP systems.
The greatest challenge of using BIM in construction project is the implementation
process itself, regardless of the software capabilities. Development of accurate BIM
model requires extensive resources and in-depth knowledge of construction methods
and process. Most small or medium firm could not afford the special team and man-
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hours to aligning BIM, as Rogers Builders employs several in-house BIM specialists
to develop, maintain and operate BIM models for each project. A dual system of
AutoCADTM and BIM system functioning at same project is another major challenge
of BIM implementation. Construction managers normally need to spend tremendous
time and man hours to educate major subcontractors, materials suppliers and even
some architecture firms to integrate BIM systems into their work platform.
Other than finance and organizational issues, the project team has experienced legal
challenges as well. The use of BIM technology encourages multi-disciplinary
collaboration, which contrasts to defining responsibility to each party and then
assigning liability issues among the parties. In addition, using BIM models instead of
traditional contract documents raises questions on insurance coverage and
confidentiality exposure. Ownership and control of the model, use and distribution of
the model, and intellectual property rights are some of the issues that need to be
addressed while BIM implementation being adopted in construction industry.
Conclusion
The current construction delivery model does not support modular construction
techniques due to extensive project planning and MEP coordination involved, even
though modular building technologies offer tremendous advantages to the construction
industry. With the increased integration of BIM in construction project, incorporating
modular building technologies into project becomes more effective and desirable
because the entire planning, design, shop drawings development, manufacturing and
construction process could be streamlined. Physical conflicts between the structure,
mechanical, electrical and plumbing systems can be easily identified early in the
design process and resolution is expedited and the building trades are not restricted to
only relying on paper plans and written specifications. Further research is suggested to
focus on the organizational and legal issues evolved with implementing BIM models
in construction projects.
Acknowledgements
The authors deeply appreciate Mr. Alistair Lowe and Mr. Geoffrey Brown, with
Rodgers Builders Construction Companies, Charlotte, NC, for their generous sharing
project data and BIM modeling systems.
References
Barton (1983) Building Services Integration, E. & F. N. Spoon Ltd., London, 1983.
CRC Construction Innovation (2007) Adopting BIM for Facilities Management:
Solutions for Managing the Sydney Opera House, Cooperative Research Center for
Construction Innovation, Brisbane, Australia.
Eastman, C; et al (2008) BIM handbook: A Guide to Building Information Modeling
for Owners, Managers, Designers, Engineers and Contractors, John Wiley and Sons,
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Edge, M, et al (2002) Overcoming client and market resistance to prefabrication and
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Gann, D. M. (1996) Construction as a manufacturing process, Construction
Management & Economics, 14(6) 437-450.
Gibb, A. G. F. (2001) Offsite fabrication: prefabrication, preassembly and
modularization. Whittles Publishing, UK.
Hsish, T. Y. (1997) The economic implication of subcontracting practice on building
prefabrications. Automation in Construction
KBS, 2009, www.bimx.com/2009/10/modular-construction-bim.html
Korman, T. M. (2001) Integrating Multiple Products over their Life Cycle: An
Investigation of Mechanical, Electrical, and Plumbing Coordination. Ph.D. Thesis,
Stanford University, Stanford, CA, June 2001.
Lu, N (2007) Investigation of the designers’ and general contractors’ perceptions of
offsite construction techniques in the United States construction industry, Doctor
Dissertation, Clemson University, Clemson, SC, May 2007.
Lu, N (2008) Designers’ and general contractors’ perceptions of offsite construction
techniques in the United State construction industry, International Journal of
Construction Education and Research, V (4) 3, pp177-188.
O’Brien M, Wakefield, R., and Beliveau, Y. (2000) Industrial the residential
construction site, U.S. Department of Housing and Urban Development Office of
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Pasquire, C.L., and Gibb, A.G.F. (2002) Considerations for assessing the benefits of
standardization and pre-assembly in construction. Journal of Financial Management
of Property and Construction, 7(3), 151-161.
Tao (2001) Mechanical and Electrical Systems in Buildings, Prentice Hall, Colum-
bus, 2001.
Tatum, C.B., and Korman, T. M (2000) Coordinating Building Systems: Process and
Knowledge. ASCE Journal of Architectural Engineering, Volume 6, No. 4, December
2000, pp. 116-121.
Vebables, T. et al (2004) Modern methods of construction in Germany. Report of a
DTI global watch mission.
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View publication statsView publication stats
https://www.researchgate.net/publication/269142172
Implementation of Building Information Modeling (BIM)
in Modular Construction: Benefits and Challenges
Na Lu1 and Thomas Korman2
1. Assistant Professor, Department of Construction Management and Engineering
Technology, University of North Carolina at Charlotte, Charlotte, NC, USA (704)
687-2718, Email: na.lu@uncc.edu
2. Assistant Professor, Construction Management Department, California State
University, San Luis Obispo, CA, USA (805)756-5612, Email:
tkorman@calpoly.edu
Modular Construction consists of one or more structure units fabricated in a
manufacturing plant away from the jobsite. In the building industry, prefabricated
modules are normally completed with trim work, electrical, mechanical and plumbing
installed. Previous studies have proved that Modular Construction provided many
advantages to the built environment, including the reduction of need for workforce,
the reduction of onsite Green House Gas (GHG) emissions, and the improvement of
construction schedule and product quality; however the extensive demand of pre-
project planning and coordination among members of cross-interdisciplinary
professionals have significantly impeded the application of this technique. With the
recent development of Building Information Modeling (BIM), these challenges could
be overcome through the BIM platform. Through case studies the benefits and
challenges of implementing BIM in modular construction are clearly identified.
Keywords: Building Information Modeling, Coordination, Prefabrication,
Building Systems.
Introduction
Modular construction refers to factory-built building units completely assembled or
fabricated in a manufacturing plant away from the jobsite, then transported and
assembled on site (Pasquire, 2002). Modular building normally consists of multiple
rooms with three-dimensional units, which are constructed and pre-assembled
complete with trim work, mechanical, electrical and plumbing components installed
(O’Brien, 2000). A large portion of construction research conducted in the United
States and globally discusses that the use of modular construction provides many
significant advantages, including: 1) the reduction of overall project schedules, 2) the
improvement of product quality, 3) increased onsite safety performance, 4) a
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reduction in the need for onsite skilled workers, and 5) a decrease in the negative
environmental impact caused by construction operations (Gann, 1996; Hsieh, 1997;
Edge, 2002; Gibb, 2001; Venables, 2004; Lu, 2007). However, the coordination and
fabrication of the Mechanical, Electrical and Plumbing (MEP) systems in modular
construction has always being one of the most challenging tasks encountered in the
delivery process of modular constructions (Tatum, 2000; Korman, 2001; Lu, 2008).
The MEP coordination and fabrication process involves defining the locations for
components of building systems, in where are often congested spaces, to avoid
interferences and to comply with diverse design and operations criteria. There are
three primary reasons contributing to the challenges of MEP fabrication in modular
construction. First, the process is highly fragmented between design and construction
firms. Second, the level of technology used in different coordination scenarios has
historically varied significantly between engineers and construction contractors.
Third, historically the process did not provide a model for use by specialty contractors
plan prefabrication (Korman, 2001).
Using Building Information Modeling (BIM) to coordinate, document and fabricate
MEP systems in modular constructions appears to be an effective approach to
overcome these challenges. In 2009, Maine based Modular Construction Company
KBS has successfully delivered their recently awarded modular project by integrating
BIM technology into the design and construction process for the New Street Project,
Cambridge, MA, as presented in Figure 1 (KBS, 2009).
(a) Architecture BIM Model to present modular wall details
(b) Installation prefabricated Roofs (c) Prefabricated Wall Panels
Figure 1: BIM application in Modular Construction Projects (Tocci & KBS)
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BIM Background and Applications
BIM is commonly defined as the process of creating an intelligent and computable
three-dimensional (3D) data set and sharing the data among the various types of
professionals within the design and construction team. With BIM technology, an
accurate virtual model of a building is constructed with precise geometry and relevant
data needed to support the procurement, fabrication, on-site installation activities, as
presented in Figure 2 (Eastman et al, 2008).
(a) Structural Steel BIM Model (b) Automatic Quantity Takeoff from BIM Model
Figure 2 BIM Model Applications in Cost Engineering
(Courtesy of: Holder Construction Co, Atlanta, Georgia, USA)
The use of BIM technology allows for the creation of intelligent contextual semantic
digital models in terms of building elements and systems, such as spaces, walls,
beams, columns and MEP systems, whereas 3D CAD technology is limited to
generating drawings in graphical entities in terms of lines, arcs and circles. In addition,
BIM technology allows for a creation of a model that contains information related to
the building physical, functional and procurement information. For instance, the BIM
model would contain data about the geometry, location, its supplier, operation and
maintenance schedule, flow rates, and clearance requirements for an air-handling unit
(CRC Construction Innovation, 2007).
Using BIM technology allows designers, engineers, and construction contractors to
visualize the entire scope of a building project in three dimensions. Therefore, BIM
technology is not only defined by simply creating a 3-D data set for internal analysis.
When most professionals refer to a 3-D model today, they are only referring to a
digital 3-D data set that contains geographical representations of objects placed in
relation to each other. BIM technology is also known as the process of using a 3-D
model and associated data set to improve collaboration among project participants.
Using this collaborative approach, designers and builders can plan, in precise detail,
the location and clearances required for a complete and successful project.
The implementation of BIM systems in modular construction normally involves in the
following process:
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Visualization: ability to create a 3D presentation of building modules
geometry, location, space, contained systems in relation to each other
Modeling: ability to generate a 3D rendering tool to present the final product
and finishes to owners, designers and constructors
Code reviews: allows for building officials and fire officials could use the 3D
models with related data for code compliance reviews
Fabrication/ shop drawings: facilitates for the generation of detailed shop
drawings could be easily produced once the BIM model is completed
Communication: facilitates simultaneously creation of construction documents,
product imagery, rapid prototypes, exterior envelope, interior finishing, and
MEP fixtures of building modules. Through this single information platform,
BIM promote collaborations among the design team, consultant, constructors
and the clients
Cost estimating: provides for cost estimating, material quantifications, and
pricing to be automatically generated and modified while changes are applied
for each building module
Construction sequences: provides a complete construction schedule for
material ordering, fabrication, delivery and onsite installation of each building
systems. With the integration of 3D rendering, 4 D (3D model + scheduling
information) could be easily generated during the project design and
construction phase
Conflict, interference and collision detection: ability to determine building
system interferences which can be visually presented. For instance, an air
distribution duct for the HVAC system physically interfering with a concrete
beam
Today, there are many examples of BIM software. NavisWorksTM is a software
program that interprets all of the other software programs used by various specialty
contractors and design engineers. NavisWorksTM is to software what the Rosetta Stone
was to interpreting languages. This software has the potential to unlock and or
interpret the other 2-D CAD drawings. This program only identifies the clashes and
the individual specialty contractors need to revisit their own software programs and
revise them in order to resubmit. NavisWorksTM will then reanalyze the new shop
drawings and hopefully there are fewer or no clashes. Obviously, when there are
multiple specialty contractors involved in a project, the challenge is to create an
environment whereby everyone has worked out the details successfully.
There are many3-D graphical representation software programs available for architects
and engineers to model their project in BIM platform as well. Graphisoft’s
ArchiCADTM allows one to draw in 3-D or import a 2-D drawing and create a 3-D
model. This program allows you to toggle back and forth from 2-D to 3-D with the
click of a mouse. AutoDeskTM is a 2-D drafting program coupled with RevitTM
creating the 3-D model.
MEP Coordination in Modular Construction prior to BIM technology
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Without the use of BIM system MEP coordination, prefabrication phase in modular
construction begins after the design and preliminary routing of all building systems
(mechanical, plumbing, electrical, etc.) is complete. The design is considered complete
when engineers have sized all components (e.g., HVAC duct, pipe, conduits),
completed the engineering calculations, and produced the diagrammatic drawings.
Representatives from each of the specialty contractors (primarily HVAC wet and dry,
plumbing, electrical, and fire protection) meet to discuss their particular designs and
drawings, which indicate the proposed routing for each system to follow to service
each required location. Most specialty contractors refer to these contract drawings as
schematic design drawings. The engineers’ stamp that the engineer provides only
insures that the design of the systems will work functionally. It does not ensure that
the system will actually fit within building.
In this scenario, the design consultant remains the engineer of record (EOR) and
retains liability for the system functionality; however, these drawings are not detailed
enough to either fabricate components or construct the systems. The required size of
components, such as conductor wire, duct dimensions, and pipe diameter are called
out on the drawings, but no scaling of the components is shown in the drawings. It is
the specialty contractor’s responsibility to build the particular building system from
these design documents. This requires that the contractor produce shop drawings, also
known as fabrication drawings. The shop drawings include the detailed information
required by the specialty contractor to fabricate and install a particular building
system.
During coordination meetings, the participating specialty contractors compare
preliminary routing for their systems to identify and resolve conflicts. The MEP trades
use a sequential comparison overlay process to compare their design drawings until
they resolve all interferences. This often requires preparing section views for highly
congested areas to identify interferences. The preliminary shop drawings that each
specialty contractor brings to the meeting indicate the path preferred for each branch
of the system to reach the required locations and perform essential functions.
Architectural, structural, and diagrammatic drawings constrain this routing. Within
these constraints, specialty contractors route systems based on the lowest cost;
however, they generally do not consider the other systems. They also decide which
specialty contractor(s) will revise their design and submit requests for information
regarding problems that require an engineering resolution. The product of this process
is a set of coordinated shop drawings that the specialty contractors submit to the
design engineer for approval that the system functionality has not been compromised.
Using BIM for MEP Coordination in Modular Construction
Historically, there has been a wide variation in the level of technology used in the
MEP coordination process. At the low-tech end of the spectrum, specialty contractors
drafted plan-views on translucent media and prepare section-views when necessary. At
the other extreme, progressive contractors have used 3D CAD to improve the process.
With the recent development of BIM, the process has gravitated toward the use of
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BIM software.
There are many locations in buildings that repeatedly cause coordination problems.
These include building corridors, points of entry and exit, openings in shear walls, and
vertical utility chases. Reserving space for access is more easily accomplished using
BIM models. However, often times resolving interferences most frequently entails
determining which building system has priority. In these cases priority is typically
determined by evaluating the functionality of each system. In the event of
interferences or clashes, the newly proposed route must be evaluated to determine if
the new route changes the systems’ functionality. If it is determined that the new route
affects the functionality of the system performance, it is given priority over another
system.
The need for MEP coordination grows out of the lack of detailed design provided for
fabrication and installation of building systems, and exists regard-less of the project
delivery process used. The current conditions in the design and construction industry
drive current practice for MEP coordination. The use of BIM technology has created
an opportunity to improve the current process by changing the way design engineers
and construction contractors interact with each other during the coordination process.
BIM offers parties involved in MEP coordination to take the opportunity to align goals
and define requirements during the construction of the model. In addition, when
historically MEP design consultants have not considered constructability issues and
made assumptions about constructability or ignore the issue totally, the use of BIM
allows a mechanism for dialogue between specialty contractors who install the system
and design engineers who design the system.
Benefits and Challenges of BIM Implementation: Case Studies
The following case studies document the implementation of BIM in two different
types of commercial projects. Specific examples of using BIM facilitating MEP
coordination in Modular Construction are discussed as well. The project and owners
name are anonymous for confidentiality purpose. The construction manager was
Rogers Builders, headquartered at Charlotte, NC. The company has over 350
associates and nationally ranked among Top 100 CM-at-Risk firm by Engineering
News Record (ENR) and Top 10 Healthcare General Contractors by Modern
Healthcare for the last 10 Consecutive years. The company has implemented BIM
system for every project they have built since 2007, with no premium cost to the
owner side. Rogers Builders maintain that the cost for development and maintenance
of BIM model with in-house resources is controlled at 0.1% of total project cost.
Case Study 1: Healthcare Expansion Project, Charlotte, North Carolina, USA
Project Scope: $44Million, 110,000 SF healthcare expansion project
Modular Construction: prefabricated concrete panels are used for floor slab
Delivery Methods: CM @ Risk
Contract Type: Cost Plus with Guaranteed Maximum Price
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Design Assistant: No Design Involvement
BIM Implementation Cost: $44000
BIM Implementation Saving: $220,000
BIM Platform: NavisworkTM
(a) Structural BIM Model (b) Architecture BIM Model (C) MEP BIM Model
Figure 3 BIM Models in Healthcare Expansion Project
(Courtesy of: Rogers Builders, Charlotte, NC, USA)
For this project, the BIM model produced architecture, structural systems and MEP
systems. It was developed to provide a dynamic platform for inter-disciplinary
collaborations as presented in Figure 3. Through the entire project management phase,
Roger Builders used the BIM models for cost engineering, subcontractor buyout, MEP
coordination and clash detection. The specific benefits have been identified by using
BIM model in this project includes:
Clearly defined subcontractor’s work scope
Automatic quantity extraction of structural steel and major MEP systems
Facilitate shop drawing of structural steel and MEP systems
560 clash conflicts between MEP systems and the structural systems were
identified prior to the fabrication of the MEP and structural systems
Case Study 2: High School Project, Gastonia, North Carolina, US
Project Scope: $38 Million, 220,000 SF High School Project
Modular Construction: Prefabricated classroom with rough-in MEP installation
Delivery Methods: Design- Build
Contract Type: Cost Plus with Guaranteed Maximum Price
Design Assistant: Extensive Design Involvement
BIM Implementation Cost: $38000
BIM Implementation Saving: N/A
BIM Platform: NavisworkTM
A comprehensive BIM model with overlapped architecture, structural, MEP model has
been created by Rogers Builders BIM specialists at the design phase of the project, as
presented in Figure 4.The BIM model was used extensively for design coordination,
subcontractor work scope clarifications, cost engineering, MEP coordination and
project sequencing.
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(a) 1st Floor BIM Model (b) 2nd Floor BIM Model
Figure 4 High School B Project BIM Model
(Courtesy of: Rogers Builders, Charlotte, NC, USA)
All MEP coordination was conducted through the BIM platform. It is very beneficial
to have fully integrated architecture, structural systems, and MEP systems in single 3D
file, which reduces change for human error and provides a visual check for
interferences for clash detections. By using the BIM model for this project, 258
conflicts were identified and eliminated during the design phase, as presented in
Figure 5 and Figure 6. Each classroom module was accurately manufactured offsite
with rough-in plumbing pipes and electrical conduits installed. The finishing MEP and
furnishing process began after the installation of each classroom module.
Figure 5 Ductwork Conflicts Structural Steels Figure 6 Ductwork conflicts with Bar Joists
(Picture Courtesy: Rogers Builders, Charlotte, NC, USA)
Through these case studies, the researchers identified that the most effective use of
BIM models was for design coordination, walk-through animation and clash
detections. This was more so for modular construction project which requires
extensive design coordination especially for MEP systems.
The greatest challenge of using BIM in construction project is the implementation
process itself, regardless of the software capabilities. Development of accurate BIM
model requires extensive resources and in-depth knowledge of construction methods
and process. Most small or medium firm could not afford the special team and man-
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hours to aligning BIM, as Rogers Builders employs several in-house BIM specialists
to develop, maintain and operate BIM models for each project. A dual system of
AutoCADTM and BIM system functioning at same project is another major challenge
of BIM implementation. Construction managers normally need to spend tremendous
time and man hours to educate major subcontractors, materials suppliers and even
some architecture firms to integrate BIM systems into their work platform.
Other than finance and organizational issues, the project team has experienced legal
challenges as well. The use of BIM technology encourages multi-disciplinary
collaboration, which contrasts to defining responsibility to each party and then
assigning liability issues among the parties. In addition, using BIM models instead of
traditional contract documents raises questions on insurance coverage and
confidentiality exposure. Ownership and control of the model, use and distribution of
the model, and intellectual property rights are some of the issues that need to be
addressed while BIM implementation being adopted in construction industry.
Conclusion
The current construction delivery model does not support modular construction
techniques due to extensive project planning and MEP coordination involved, even
though modular building technologies offer tremendous advantages to the construction
industry. With the increased integration of BIM in construction project, incorporating
modular building technologies into project becomes more effective and desirable
because the entire planning, design, shop drawings development, manufacturing and
construction process could be streamlined. Physical conflicts between the structure,
mechanical, electrical and plumbing systems can be easily identified early in the
design process and resolution is expedited and the building trades are not restricted to
only relying on paper plans and written specifications. Further research is suggested to
focus on the organizational and legal issues evolved with implementing BIM models
in construction projects.
Acknowledgements
The authors deeply appreciate Mr. Alistair Lowe and Mr. Geoffrey Brown, with
Rodgers Builders Construction Companies, Charlotte, NC, for their generous sharing
project data and BIM modeling systems.
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What you have:
1) Draft word file
2) Feedbacks and comments
3) 1 thru 14 pdf files that were used for draft section. You can go back skim and check it if you need it.
Initially I started to design, thesis topic was. Affordable student housing with modular construction. Right now we change it. It will be Housing for Young professionals and Students with modular construction.
It should not be affordable. It should be economical build. If you read the project statement and objective, it will help you.
You can extend problem statement and objectives.
You can find any other sources about the modular construction to expand the BACKGROUND!
PLEASE CHECK AND GET BACK TO ME WITH YOUR QUESTIONS…