Influence of Mass Irregularity on the Response of RC Frame with Stiffness Irregularity by Non-linear Time History Analysis

It is generally observed that the seismic design codes take only single seismic event into consideration ruling out the possibility of successive events. The buildings in earthquake-prone areas subjected to such loading are susceptible to collapse as they get little or no time to retrofit them. It is observed that the seismic demands go on incrementing after the occurrence of every aftershock that succeeds the mainshock. The damage caused during the aftershocks depends upon the damage produced by their preceding mainshocks. Plastic state/collapse of the structure subjected to sequential ground motion is governed by the degree of damage, i.e., residual displacements occurred during mainshock. The present study comprises of an 11-storey frame considered under the influence of a number of sequential ground motions obtained by increasing the peak ground acceleration of mainshock from 0.36g to 0.45g and aftershocks of two-third of their respective PGA. Mainshocks with increasing peak ground acceleration have been generated synthetically using the design response spectrum described in the IS code IS1893:2016 predicted on NDA with the help of SAP 2000 software. Irregularities are introduced in the first, sixth, and top storey of the frame to study the influence of mass irregularities on the response of the frame with stiffness irregularities. This study does an in-depth analysis on the inelastic response of the frame taking into account the maximum top displacement, location of plastic hinges, maximum storey drift, and residual displacement.