Performance of RC Frames with Stiffness Irregularity Under Sequential Ground Motion

Quite often buildings in high seismic zone are subjected to mainshock and subsequent aftershocks with little time to retrofit/repair the buildings. In this work, a G + 10 storey 2D regular frame in zone V (IS1893) has been designed using the response spectrum method. Nonlinear dynamic analysis has been done on the designed frame subjected to time history compatible with IS1893:2016. The frame is further loaded with six aftershocks of 66% peak ground acceleration of mainshock with a time lapse of 100 s after every shock. SAP2000 has been used to model the frame and its analysis. Stiffness irregularity is introduced in the ground, first, fifth, and top storey one at a time, and each of the frames with the irregularity has been analyzed for the mainshock, and subsequent aftershocks. The maximum top displacement, location of plastic hinges formation, residual displacement after each shock, and maximum storey drift are found out to investigate the response of a regular/irregular four-bay, ten-storey RC frame. Response of the considered regular/irregular frames have been compared. Residual drift and top residual displacements are found to be accumulating with each aftershock. 0.4 g and 0.45 g PGA with aftershocks lead to failure of the frame.