Mainshock–aftershock Fragility Analysis of RC Structures Considering IP-OOP Interaction of Infill Masonry Walls

In this study, the three-dimensional numerical model of a reinforced concrete (RC) structure considering the in-plane and out-of-plane (IP-OOP) interactions of infill masonry wall was established using the OpenSees platform. The damage state-dependent aftershock fragility curve was obtained using the binary logistic-regression method. Finally, the seismic resistance was assessed based on the performance margin ratio. The results indicated that the fragility curves considering the IP-OOP interaction are lower than that without considering the infill wall interactions, and the variability of fragility curves is distinct as the damage state worsens. The vulnerability for damages from the aftershocks depends on the initial damage to the structure induced by the mainshock. As the mainshock damage increases, the probability of more severe damage under aftershock also increases. In addition, under mainshock-aftershock sequence, the intact structure may not attain the seismic prevention target of no damage during the frequent earthquakes. Similarly, the damaged structure might not meet the requirements of repairability under design-basis earthquakes and no collapse under maximum considered earthquakes when the initial damage of the structure is light and moderate under mainshock.