SEISMIC DESIGN OF A STEEL TRUSS RAIL-CUM-ROAD BRIDGE USING CONVENTIONAL AND BUCKLING-RESTRAINED BRACES

Among different types of bridges, two-tier rail-cum-road bridges are particularly susceptible to seismic loading because of loading at two different levels. This paper, based on the seismic design of such an existing steel truss bridge in India, reduces the design base shear for the bridge with respect to the traditional design practice by utilising the ductility of the steel superstructure. Non-linear static analysis (NLSA) is conducted to evaluate the response reduction factor (R) for two models, one having only conventional braces and the other one with Buckling-Restrained Braces (BRBs), installed judiciously so as to decrease the design base shear even further. Although the latter is observed to have a higher R value, it is achieved at the cost of higher deformations. Certain performance criteria are defined to judge the operability of the bridge following an earthquake. Pushover analysis is conducted on each model to assess its performance at different levels of earthquake and the results are compared to conclude the advantages and disadvantages of the second model with respect to the former.