Seismic performance of RC frames under sequential ground motion

The current practice of the seismic design of buildings relies on a single event of earthquake having a specified intensity measure. Two-level earthquakes are used along with the specified design response spectrum for arriving at the seismic design forces. The seismic performance of the designed structure is evaluated using non-linear time history analysis for some specified ground motion or synthetically generated ground motion from the response spectrum. No consideration is paid to the aftershock event, which is commonly associated with any major shock. The present study investigates the adequacy of the current design practice to cater to the aftershock events using 11-storey RC frame subjected to a sequence of main- and aftershocks synthetically generated from the design response spectrum as specified in the IS code. Several seismic demand parameters, namely, transient and residual top displacements, maximum inter-storey drift, residual storey drift, base shear and a number of plastic hinges, are used to evaluate the seismic performance of the frame for each earthquake shock. The result of the study indicates that with the increase in the number of aftershocks, significant deterioration of strength and stiffness takes place, resulting in the residual demand parameters exceeding the permissible limit.