Modified seismic fragility analysis of reinforced concrete frame structures in consideration of collapse probability

A modified seismic fragility analysis method was presented to examine the effect of collapse probability on non-collapse limit states. This method, based on the total-probability theory, divided structural limit states into two categories as collapse limit states and non-collapse limit states. When the structure occurring collapse, the exceeding probability of non-collapse limit states were taken as 100%. Both a direct method and an indirect method were included in the presented method, where the direct one modified the parameters of fragility functions directly, while the indirect one only modified probabilistic seismic demand parameters. Four reinforced concrete frame structures designed for different heights and different earthquake fortification levels were taken as the study cases. A suite of 100 real ground motion records were selected as the earthquake inputs, and the modified seismic fragility analysis using the direct method and the indirect method was conducted. The results show that the collapse probability has ignorable effect on the limit states of slight damage and moderate damage, where it has a significant effect on the limit state of server damage. The two methods for modifying seismic fragility values result in similar results under small earthquake intensities. With increasing earthquake intensities, the seismic fragility values modified by different strategies are becoming significantly different.