Quantifying the Reduction in Collapse Safety of Main Shock–Damaged Reinforced Concrete Frames with Infills

A performance-based methodology is presented to quantify the reduction in collapse safety of main shock–damaged reinforced concrete frame buildings with infills. After assessing their collapse safety in the intact state, the residual collapse capacity following main shock damage is evaluated by conducting incremental dynamic analysis to collapse using main shock–aftershock ground motion sequences. The median collapse capacity and conditional probability of collapse for the main shock–damaged building, normalized by that of the intact case are the metrics used to measure the reduction in collapse safety. Taller buildings with built-in soft and weak first stories have the highest reduction in collapse safety as a result of main shock damage. Among the engineering demand parameters recorded during the main shock analyses, story drift demands (peak transient and residual) and infill strut axial deformations have the highest correlation with the decline in collapse performance. The results of the main shock–aftershock incremental dynamic analysis to collapse are used to develop fragility functions for the limit state defined by the building being structurally unsafe to occupy.