Seismic response of RC frames under far field mainshock and near fault aftershock sequences
Engineered structures built in seismic prone areas are affected by aftershocks in addition to mainshocks. Although aftershocks generally are lower in magnitude than that of the mainshocks, some aftershocks may have higher intensities; thus, structures should be able to withstand the effect of strong aftershocks as well. This seismic scenario arises for far field mainshock along with near field aftershocks. In this study, four 2D reinforced concrete (RC) frames with different numbers of stories were designed in accordance with the current Iranian seismic design code. As a way to evaluate the seismic response of the case study RC frames, the inter story drift ratio (IDR) demand, the residual inter story drift ratio (RIDR) demand, the Park Ang damage index, and the period elongation ratio can be useful engineering demand parameters for evaluating their seismic performance under mainshock aftershock sequences. The frame models were analyzed under a set of far field mainshock, near fault aftershocks seismic sequences using nonlinear dynamic time history analysis to investigate the relationship among IDR, RIDR, Park Ang damage index and period ratio experienced by the frames. The results indicate that the growth of IDR, RIDR, Park Ang damage index, and period ratio in high rise and short structures under near fault aftershocks were significant. It is evident that engineers should consider the effects of near fault aftershocks on damaged frames that experience far field mainshocks as well.