Aftershock Fragility Curves and Tagging Assessments for a Mainshock-Damaged Building

When multiple earthquakes occur within a short period of time, damage may accumulate in a building, affecting its ability to withstand future ground shaking. This study aims to quantify the post-earthquake capacity of a nonductile 4-story concrete building in New Zealand through incremental dynamic analysis of a nonlinear multipledegree-of-freedom simulation model. Analysis results are used to compute fragility curves for the intact and damaged buildings, showing that extensive damage reduces the structure’s capacity to resist seismic collapse by almost 30% percent. The damage experienced by the building in mainshock, can be compared with the ATC-20 building tagging criteria for post-earthquake inspections, the purpose of which is to ensure public safety. Extensively damaged buildings, which are likely be red tagged, pose a significant safety hazard due to decreased strength in future earthquakes. The effect of mainshock damage is also compared for multiple and simplified single-degree-of-freedom models of the same building.