Assignment 225
Running head:
DESIGN OF STEEL TRUSS BRIDGE
1
DESIGN OF STEEL TRUSS BRIDGE 10
DESIGN OF STEEL TRUSS BRIDGE 9
DESIGN OF STEEL TRUSS BRIDGE
STUDENT NAME
INSTITUTION
DATE
Abstract
This project is mean to design a steel truss bridge which will be located in one of the highways, still, unspecified. The bridge will have the following specifics, it will be arch type steel truss bridge, the bridge span will be 40m, no peers or cables will be used. The bridge will be designed in such way that it will be robust enough to support a minimum truck weight of 225kN, it will also have two lanes which are reversible to allow for easy traffic control. To ensure that the bridge will be robust enough as per the design requirements, analysis of the two most critical elements shall be done using the West Point Bridge Designer Software. After that, hand calculations shall be done, then compared with the results gotten from the West Point Bridge Designer Software. In case of any discrepancies, both calculations, in the software and hand calculations shall be repeated. If the discrepancies arise again, then replacement of the element shall be considered. It should be noted that arch type steel truss bridge has been selected after analysis of the conditions of use such as the maximum load per unit area expected and analysis of types of bridges including: Beam Bridge, truss bridge, Cantilever Bridge, arch bridge, tied arch bridge, suspension bridge and cable-stayed bridge. After analysis of all these types, it was found that the best bridge type was arch type steel truss bridge
Introduction
Bridges normally exist in different types of designs depending on the condition of use and load to be supported. Each type has its own design specification suited to for area or condition of use. To select a bridge type, analysis of the condition of use must full be done before the selection. The bridge types vary in terms of load they can support, cost, design and the areas of use. Some of the commonly known bridge types are:
1. Beam Bridge
2. Truss Bridge
3. Cantilever Bridge
4. Arch Bridge
5. Tied Arch Bridge
6. Suspension Bridge
7. Cable-Stayed Bridge
Beam Bridge
A beam bridge is one of the common bridges because it is the easiest bridge type to construct. An example of a beam bridge is the basic log bridge which is easy, simple and cheap to design. Traditionally, the area which support the load was either made of stone or wood. They were then supported on both sides by two beams located between the abutments. At times, it becomes necessary to add additional beams between the main beans to offer more support and make the bridge more stable. The area which is expected to support the load is normally a simple deck which is situated across the underlying beams vertically(Jiang, Feng et al. 2019). Example of Beam Bridge is shown in the figure 1 below.
Fig 1: A beam bridge at Lowa River (Mark 2019).
Truss Bridge
This type of bridge has been there for many centuries. It has a simple load carrying structure design that integrates a truss which is very reliable. There might be different in the design of the truss bridges but all of them involve the use of triangular sections as shown below in figure 2(Ryall, Hewson et al. 2000).
Triangular section
Fig: Triangular sections in a truss bridge
In this type of bridge, the tension and the compression forces are absorbed by the triangular section, hence making the structure to be robust enough to accommodate any dynamic loads. On the other hand, a combination of the tension and the compression forces ensure that the bridge structure is maintained accurately and that the load carrying area is not compromised by any dynamic load such as strong blowing winds. The figure 3 below shows this type of bridge.
Fig 3: A truss bridge at Francis Scott Key Bridge, Baltimore (Dharrah87 2018).
Cantilever Bridge
The working principle of this type of bridge is based on applying cantilevers that can be either beams or trusses. In this type of beam, the horizontal beams which are forming the cantilever arm are supported from one side only which might make them look somehow dangerous. The two cantilever arms however are supported a suspended span which is effective and located at the center(Natário, Ruiz et al. 2015). This suspended span has no direct support coming from beneath. As opposed to other bridge types which use vertical bracing, this type of bridge uses a diagonal bracing with horizontal beams to support the load.
A cantilever bridge is shown in figure 4 below.
Fig 4: Cantilever bridge at Forth Bridge, Scotland (Andrew 2016).
Arch Bridges
This type of bridge also has its types on its own. But what makes all those types to be common is the abutment which is very vital in supporting the arch structure which is curved and located beneath the bridge. In this case, the laterally acting pressure due to the arch span is transmitted to the abutments which are the core supports(Liu, Guo et al. 2014). Therefore, abutments are very important parts which at all times must be intact and well founded. Many arch bridges normally have well decorated brickworks which play a very crucial role in the bridge design. An example of the arch bridge is shown in figure 5 below.
Fig 5: An arch bridge at Gaolaing Bridge of the summer palace (Hennessy 2015).
Tied Arch Bridge
This type of bridge involves use of a metal arch structure which is supported by the vertical tiers which are located in the middle of the arch and the deck. The arch structure tips are then joined together using the bottom chord. The arch structure generates a downward pressure which is directed to the deck, but this pressure is converted to tensional force by the vertical ties(De Backer, Outtier et al. 2014). In this type of bridge, the bottom chord connecting the ach structure tips puts in place the arch structure and the tied arch bridge as opposed to abutments as majority of the people think. The figure 6 below shows an example of a tied arch bridge.
Fig 6: Tied arch bridge at Infinity Bridge in Stockton-on-Tees (Logic 11)
Suspension Bridge
In its design, this type of bridge might seem to be simple, but in reality under working condition, this type of bridge is very reliable(Fenerci, Øiseth et al. 2017). Its deck being the element carrying the load for the whole structure. This deck is positioned by several vertical suspenders that aids the cable also. These suspension cables are firmly anchored into the ground and then extend out past each side of the bridge. For the suspension cables to be in place, some towers must be constructed to hold them up. The number of towers to be constructed will be determined by the load size which the bridge will carry and the bridge size itself. In this type of bridge, these cables are very vital as they transforms any load which exerted in the bridge into tension force. It’s common at some point to experience slight movement of the cable due to the expansion and contraction of the suspension cables depending on the weather condition. An example of the suspension bridge is shown in figure 7 below.
Fig 7: Suspension bridge at Chromolithograph of the Great East River (Currier and Ives 1883)
Cable-stayed bridge
This bridge type is fully dependent on its towers or the pylons. The towers are the load-bearing elements in the bridge. In this case, the suspension cables are joined from the towers to the deck below or from the column of the tower to the deck.(Ren, Peng et al. 2005). This type of bridge is majorly applied in cases where a longer bridge is to be constructed and it cannot be achieved by either the suspension bridge or the cantilever bridge. An example of this types of bridge is shown in figure 8 below.
Fig 8: A cable-stayed Bridge at the Rio Antirrio Bridge in Greece (David 2013).
West Point Bridge Designer Software
The West Point Bridge Designer Software is a software which have tools which can be used to model, test and optimize the steel highway bridge depending on the specifications that it has been given (Engineering Encounters 2016). This software provides a flexible platform for the user to create many designed with varied shapes and configuration hence allowing the user to experiment various designs until he/she gets the best possible solution at a low cost.
References
Andrew, S. (2016). Aerial view of the Forth Bridge, Edinburgh, Scotland. Retrieved from
https://commons.wikimedia.org/w/index.php?curid=51291330
Currier and Ives. (1883). Example of a suspension bridge. Chromolithograph of the Great East River Suspension Bridge
David, R, S. (2013). Rio-Antirrior Bridge: The World,s Longest Mult-Span Cable-System. Retrieved from: https://www.industrytap.com/rio-antirrio-bridge-the-worlds-longest-multi-span-cable-system/3756
De Backer, H., et al. (2014). Buckling design of steel tied-arch bridges. Journal of Constructional Steel Research 103: 159-167.
Dharrah87. (2018). View of the Key Bridge from the air, looking east towards Sparrows Point. Retrieved from:
https://commons.wikimedia.org/w/index.php?curid=66155538
Engineering Encounters. (2016). West Point Bridge Designer. Retrieved from https://www.cesdb.com/west-point-bridge-designer.html
Fenerci, A., et al. (2017). Long-term monitoring of wind field characteristics and dynamic response of a long-span suspension bridge in complex terrain. Engineering structures 147: 269-284.
Hennessy. (2015). Gaoliang Bridge of The Summer Palace. Retrieved from https://commons.wikimedia.org/w/index.php?curid=601984
Jiang, L., et al. (2019). Vibration characteristic analysis of high-speed railway simply supported beam bridge-track structure system. Steel and Composite Structures 31(6): 591-600.
Mark, B. (2019). The 7 types of Bridges. Retrieved from:
Liu, W., et al. (2014). Retracted: using BIM to improve the design and construction of bridge projects: a case study of a long-span steel-box arch bridge project, SAGE Publications Sage UK: London, England.
Logic. (2011). Calm before the storm, Infinity Bridge. Retrieved from https://commons.wikimedia.org/w/index.php?curid=24708545
Natário, F., et al. (2015). Experimental investigation on fatigue of concrete cantilever bridge deck slabs subjected to concentrated loads. Engineering structures 89: 191-203.
Ren, W.-X., et al. (2005). Experimental and analytical studies on dynamic characteristics of a large span cable-stayed bridge. Engineering structures 27(4): 535-548.
Ryall, M. J., et al. (2000). The manual of bridge engineering, Thomas Telford.