OPTIMIZATION OF TRUSS TYPE STEEL BRIDGES

This work aims towards analyzing truss type steel bridges by 3-D finite element modelling using SAP2000. Details of different truss type steel bridges are discussed together with gathered information on such bridges found in Sri Lanka. State of the art, regarding design and assessment of truss type steel bridges were also reviewed. Scale-down model bridges were tested in the Structural Laboratory (UOM) and the test results were used to validate the SAP models and observe the overall behaviour. The actual failure loads and failure patterns were observed and compared with SAP analysis results. 3-D [mite element modelling gives a clear image in modelling of truss type bridges, than 2-D finite element counterparts due to the facilities available to check the lateral stability of the bridges. This research contains some methods to improve the lateral stability of truss type steel bridges too. Failure study and analysis were done for some failed bridges in Sri Lanka using SAP 2000. Results predicted by SAP 2000 are compared with actual failure modes, loads and deflections. Span vs. tonnage graphs were obtained with optimum steel usage, for the selected truss type steel bridges which include common truss types used in the country and some of other efficient truss types. It contains span vs. tonnage graphs which were obtained for Modified Warren, Parker, Inverted Arch, Pratt and Tied Arch bridges which are used for pedestrians and light vehicles. The weights of the actual existing bridges are presented in the same graph (if applicable) and the reasons for deviation from the graph are also discussed. Set of span vs. tonnage curves were plotted for different truss types in same graph, for comparison purpose which shows tonnage required for each selected truss type, for given range of spans. Finally, some guidelines for local bridge designers, and some suitable truss types are recommended by considering minimum steel usage