Field evidence from recent earthquake indicates that strong aftershocks have the potential to cause severe damage or even collapse to structures. This paper aims to investigate the influence of aftershock on the seismic performance assessing results of bridge considering cumulative damage effect. For that purpose, a damage evaluating approach for continuous girder bridge is employed that includes two integral parts: deteriorating numerical modeling and a combined damage index that considers both large deformation and cyclic loading effects. To investigate the influence of aftershock, a continuous girder RC bridge was selected and nonlinear incremental dynamical analysis subjected to mainshocks and mainshock-aftershock sequences was conducted. The fragility curves were finally generated. Comparisons were also made to investigate the difference of the result due to whether the cumulative damage is considered or not. From the analysis results, it was found that, for continuous bridges, aftershocks can considerably increase the seismic demand as well as fragility. In addition, for moderate damage fragility, the influence of aftershock is greater when cumulative damage is considered.
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