Impact of as-recorded mainshock-aftershock excitations on seismic fragility of corrosion-damaged RC frames

The experience from the past seismic events shows that the accumulated damage induced by the previous earthquakes increases the vulnerability of Reinforced Concrete (RC) structures. Moreover, RC structures constructed in aggressive environments such as those located in the coastal area suffer from the ageing and degradation phenomena. Therefore, the concurrent influence of successive seismic hazards and corrosion-induced degradation might result in undesired seismic failure of these RC structures. From this perspective, this paper investigates the seismic performance of RC frames affected by chloride-induced corrosion of reinforcements subject to as-recorded (real) mainshock-aftershock excitations. To this end, a prototype RC frame is analysed under real mainshock-aftershock ground motions at different times since corrosion initiation. First, a suite of mainshock-aftershock records is selected from a unique database using the Conditional Mean Spectrum (CMS) methodology. Then, an advanced numerical model capable of tracking the low-cycle fatigue degradation and inelastic buckling of reinforcements is used to simulate the nonlinear dynamic behaviour of the studied frames with different levels of corrosion. Finally, the seismic performance and fragility of the considered structures are evaluated using the outputs of nonlinear static and incremental dynamic analyses. The results show that the vulnerability of corroded reinforced concrete frames is significantly increased under successive earthquake events. Moreover, the results of this paper show that the probability of failure of corrosiondamaged RC frames depends crucially on the magnitude of the aftershocks.