SEISMIC FRAGILITY ANALYSIS OF RC FRAME UNDER MAINSHOCK-AFTERSHOCK SEISMIC SEQUENCES USING INCREMENTAL DYNAMIC ANALYSIS

The reinforced concrete (RC) frame represents a major structure type for residential buildings in China. At the design stage, the seismic perfoiniance of RC frame is typically addressed by considering the attack of one major earthquake within a given return period. However, evidences from recent earthquake events demonstrate that a RC frame might be severely damaged by mainshock-aftershock seismic sequences due to the damage accumulation even though the frame might perform well under mainshock attack only. Therefore, it is imperative to learn the performance of RC frame under mainshock-aftershock seismic sequences. To this end, this paper investigates the seismic fragility of a 6-story RC frame model under mainshock-aftershock seismic sequences using the incremental dynamic analysis (IDA), which is a parametric analysis method widely used to estimate structural performance under seismic loads. Ten mainshock-aftershock seismic sequences records have been chosen from Pacific Earthquake Engineering Research Center (PEER) database. Each record was applied to the model to get an IDA curve resulting in total ten curves, from which an average IDA curve was obtained. Finally, the seismic fragility analysis is carried out on the basis of the results of IDA. The comparison of failure probabilities between mainshock and mainshock-aftershock shows that aftershock has the potential to increase the damage of the structure and the effects of aftershock should be considered at the design stage in order to ensure the safety of the structure. The results provide a basis for achieving cost-effective mitigation of risk from competing mainshock-aftershock seismic sequences and a policy-making decision for reinforcing and maintaining of existing RC frames in the future. Only RC frame structure is considered in this paper and more work need to be done to study the effects of aftershock on other structures.