Development of damage state-dependent fragility functions for a MDOF structure through dynamic analyses with successive un-scaled time-histories

Abstract : In the context of a seismic crisis where successive aftershocks threaten to bring down previously damaged structures, damage state-dependent fragility curves may constitute a useful tool to reassess the updated vulnerability of the exposed structures. This study builds on a methodology to derive state-dependent fragility curves without record-scaling and suggests some improvements. A set of natural ground-motion records is applied multiple times to a 2D model of a reinforced-concrete moment-resisting frame building with hysteretic degradation. The relationship between the aftershock intensity measure and the engineering demand parameter (here the maximum transient drift ratio) is obtained in two steps: A modified least-squares regression is first performed between the maximum additional transient drift ratio achieved during simulation and the intensity measure, and the results are then compounded with the distribution of the initial residual drift ratio. A comparison is finally made with fragility curves derived using an incremental dynamic analysis (IDA) approach.