Shock-Aftershock Effect Analysis for Seismic Performance Evaluation of RC moment Frames

Sequential quakes as shock-aftershocks result in nonlinear response of buildings and in many cases lead to severe destruction such as accumulative structural damages in compare to single shock quakes. In current study, the shock-aftershock sequence effect on the nonlinear seismic performance of reinforced concrete (RC) moment frames is studied in detail. In this way, nonlinear numerical method is selected as the study approach and preliminary models are calibrated based on existing shake-table experiments. In advance, four-story and eight-story frames are modeled using flexibility-based finite element code and are subjected to quake sequences. Three types of seismic sequences are assumed for study: (1) single shock quakes; (2) similar shock-aftershock quakes; (3) dissimilar far field-near fault shock-aftershock quakes. Discussions are based on the maximum and residual inter-story drift ratios. Results reveal that the residual drifts are increased in seismic sequences. In addition, four-story frames experience higher maximum drift ratio than the eight-story frames during the aftershocks. The increase of residual drift ratio in more apparent for four-story frames than eight-story frames in the case of dissimilar seismic sequences. For all the assumed cases, top stories experience the highest values of maximum and residual drift ratios which show the sensitivity of top stories to the seismic sequence. Thus, the collapse probability of top stories is high during shock-aftershock sequences and needs to be considered in further seismic design.