Deaggregation of Collapse Risk

Avoidance of collapse is one of the most important objectives when designing structures in seismic regions. This study focuses on collapse risk quantification and, in particular, deaggregation of the mean annual frequency of collapse. Similar to the deaggregation used in probabilistic seismic hazard analysis, which provides information about the magnitudes, distances, and epsilon values that primarily contribute to the seismic hazard, deaggregation of the mean annual frequency of collapse is a powerful tool that identifies the ground motion intensities that primarily contribute to the collapse risk of a given structure. A detailed description of how to conduct this deaggregation is presented, and the concept is illustrated using a 4-story steel special moment frame building designed according to the 2003 International Building Code. The collapse risk of this structure is evaluated for sites in the western, central, and eastern United States. Despite significant differences in the seismic hazards at each site, it is shown that intensities corresponding to the lower half of the collapse fragility curve dominate the collapse risk at all sites. It is concluded that emphasis should be placed on the lower half of the collapse fragility curve as opposed to focusing on the median collapse intensity as is currently done.