Seismic Behaviour of a Typical Rail Bridge Using North-East India Specific Synthetic Ground Motions Under Multi-support Excitation

Abstract

Seismic excitations are time varying and spatially varying waveforms depending on the seismotectonics of a region. Analysis of a long structure like bridges, pipelines, dams using uniform seismic excitation is not a realistic approach as the seismic excitation does not remain stationary at every support location. Thus, multi-support seismic excitation is performed to obtain seismic responses of a structure under a realistic situation. In this paper, a replica of a five-span railway bridge (5 spans @ 26.24 m) located in the seismically active north-east zone of India has been studied. A finite element modelling of the total bridge has been created in the SAP2000 software. Synthetic ground motions of moment magnitude (Mw) 8.7 with wave velocity of 1200 m/s have been generated as per the geotechnical and geological conditions of this region considering Oldham and Dauki faults by Stochastic Model Simulation (SMSIM). The synthetic acceleration response has been used for performing nonlinear time-history analysis for both uniform and multi-support seismic excitation study. Nonlinear time-history analysis has been performed to obtain the dynamic response of the total structure due to seismic excitation. The study concludes that the absolute maximum displacement, shear force, bending moment at the total deck and the piers increase in case of multi-support seismic excitation than uniform seismic excitation. This study shows that the codal provisions should incorporate the effect of multi-support excitation and site-specific ground motion details in the design of important structures to keep them operational in extreme hazardous conditions.