Aftershock Probabilistic Seismic Demand Model of Damaged Non-Ductile Reinforced Concrete Frames in California

Current seismic design practices and risk assessment methods have not included the effect of potential post-earthquakes on building structures. However, recent seismic events have demonstrated that even small magnitude aftershocks may cause severe damage or collapse on softened structures as a result of a mainshock. To account for the cumulative damage potential and increased vulnerability of reinforced concrete building frames under multiple earthquakes, this paper proposed an analytical tool, aftershock probabilistic seismic demand model required for computing aftershock fragility functions. The analytical models of non-ductile reinforced concrete frames are built in the nonlinear finite element platform of OpenSees. Incremental dynamic analysis approach is used to generate mainshock ground motions that can produce mainshock-damaged conditions in terms of maximum interstory drifts of interest. In the next step, back-to-back time history analyses for mainshock-aftershock sequences are performed in order to develop a probabilistic seismic demand model in an aftershock environment. The demand model can be characterized in terms of an aftershock intensity measure and an initial damage state associated with a mainshock response by using a suite of ground motions representative of the seismic hazard in the region. Furthermore, these demand models are compared with different levels of existing damage conditions (different mainshocks and same aftershocks).