Impact of earthquake ground motion characteristics on collapse risk of post-mainshock buildings considering aftershocks

This paper investigates the influence of duration and frequency content of earthquakes on the collapse risk of post-mainshock buildings accounting for four damage states. The 5-95% significant duration Ds and the mean period Tm are selected as the index parameters to represent the duration and frequency content of ground motions, respectively. The modified Ibarra-Krawinkler hysteretic model is used in the structural models to capture strength and stiffness degradation associated with structural damages. The ground motion intensity is measured by inelastic spectral displacement (Sdi) to implicitly capture the spectral shape effect. Structural collapse capacities are determined using a suite of 62 records with a broad range of earthquake ground motion characteristics. The results demonstrate that both the duration and frequency content of ground motion play a significant role in structural collapse capacity. The degree of influence of aftershock characteristics on post-mainshock building collapse capacities becomes more significant as the structural damage level from the mainshock increases. As a result, post-mainshock structures with more serious damage states may be more fragile when subjected to the aftershocks with longer duration and lower frequency. Aftershocks are usually characterized by shorter duration and higher frequency than those of the corresponding mainshocks, thus the collapse risk of post-mainshock buildings may not be properly estimated using seeding scaled mainshock record as an aftershock compared to those using as-recorded mainshock-aftershock sequences.