Aftershock fragility assessment of steel gabled frames consisting of web-tapered members

Abstract

Due to the widespread construction of steel gabled frame systems throughout the world, many of them are located in regions with high seismicity and experience sequential strong events in the future. Previous studies have clearly shown that the damage caused by the mainshock modifies the overall strength and stiffness and consequently dynamic response to the aftershock. However, the current structural design process only considers the main seismic event, and the post-mainshock scenarios and their effects are generally ignored. In order to address this issue, in the present study, the mainshock incremental dynamic analysis (IDA) was first conducted on four SGFs. Then mainshock damage states based on the transient absolute maximum drift angle were considered, and aftershock incremental dynamic analysis analysis was performed on the mainshock-damaged structures. Aftershock fragility curves using probabilistic seismic demand models for transient absolute maximum drift angle and median IDA curves for residual absolute maximum drift angle were developed to compare intact and pre-damaged SGFs. The results showed that aftershocks significantly increase the vulnerability of short-period SGFs when higher damages are induced during mainshock, where the aftershock collapse capacity is reduced by up to 13% for the largest mainshock damage state. It was also found that in terms of aftershock collapse capacity associated with the residual absolute maximum drift angle, long-period SGFs require major realignment while short-period SGFs cannot be repaired.