Center for Railway Engineering

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Browsing Center for Railway Engineering by Subject "AAHSTO LRFD Bridge specification"

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    Computer Program for Deflection Chart of Simply Supported Prestressed Railway Girder
    (Addis Ababa University, 2016-01) Fiseha, Nega; Esayas, Gebreyouhannes (PhD)
    Light rail transit has been under construction in the city for the last two years and it crosses many intersection and roundabouts. Most of the time the rail crosses the road with elevated bridge using a prestressed girder but due to design limitation the span of the bridge is limited and this leads to a number of closely spaced piers in the city centers which interferes with the traffic flow and causes more traffic congestion to the ever growing city of Addis Ababa. Traffic congestion around intersection and round about is the major problem in big cities like Addis Ababa. Therefore when other infrastructure interferes with the existing flow the problem is worse. And one of the main factors that limit the span of the structure is deflection requirement. Therefore being able to assess and know the deflection of prestressed girder as precisely as possible will indeed help in designing an economical large span girders. In designing prestressed girder, calculating deflection the necessary and rigorous step which one has to calculate at the end of the design process and tell whether the design girder is within the allowable limit or not. If it is not the designer has to change the cross sectional dimension and repeat the whole step once again. But if the designer can certainly know the deflection of that structure in advance of those steps he/she can eliminate such iteration. Therefore this thesis intended to develop a program that plot a deflection chart for simply supported prestressed railway girder. MATLAB programing language has been used to develop the program of deflection calculation and to plot the chart. Microsoft excel has also been used to develop a deflection calculation template for checking purpose. Mainly AAHSTO LRFD Bridge specification, American Concrete Institute (ACI) publications and American Railway Engineering and Maintenance-of-way Association (AREMA) has been used in this thesis but other important material has also been referred when needed. The findings were one can control the deflection or camber of the prestressed member with the magnitude of the applied load and varying the eccentricity of the tendon profile both at the support and at the mid-span. However the deflection vs. span length chart will show some unexpected behavior after a certain span length. It suddenly changes is dimension and direction in unanticipated manner. And this leads to the development of another chart “the design chart” which tells the minimum prestressing force needed and the working range of a certain geometric section for a given load. And from this we notice that for a given load and a given cross-sectional geometry a prestressed member has not only a maximum span length limit but also a minimum span length limit in order to serve the intended function without failure.