Impact of hazard-consistent ground motion duration in structural collapse risk assessment
© 2016 John Wiley & Sons, Ltd. This study evaluates the effect of considering ground motion duration when selecting hazard-consistent ground motions for structural collapse risk assessment. A procedure to compute source-specific probability distributions of the durations of ground motions anticipated at a site, based on the generalized conditional intensity measure framework, is developed. Targets are computed for three sites in Western USA, located in distinct tectonic settings: Seattle, Eugene, and San Francisco. The effect of considering duration when estimating the collapse risk of a ductile reinforced concrete moment frame building, designed for a site in Seattle, is quantified by conducting multiple stripe analyses using groups of ground motions selected using different procedures. The mean annual frequency of collapse (λ collapse ) in Seattle is found to be underestimated by 29% when using typical-duration ground motions from the PEER NGA-West2 database. The effect of duration is even more important in sites like Eugene (λ collapse underestimated by 59%), where the seismic hazard is dominated by large magnitude interface earthquakes, and less important in sites like San Francisco (λ collapse underestimated by 7%), where the seismic hazard is dominated by crustal earthquakes. Ground motion selection procedures that employ causal parameters like magnitude, distance, and Vs 30 as surrogates for ground motion duration are also evaluated. These procedures are found to produce poor fits to the duration and response spectrum targets because of the limited number of records that satisfy typical constraints imposed on the ranges of the causal parameters. As a consequence, ground motions selected based on causal parameters are found to overestimate λ collapse by 53%.