This study examines the influence of ground motion duration on the collapse capacities of a modern five-story steel moment frame and a reinforced concrete bridge pier. The effect of duration is isolated from the effects of ground motion amplitude and response spectral shape by assembling sets of “spectrally equivalent” long and short duration records and employing them in comparative nonlinear dynamic analyses. For the modern steel moment frame, the estimated median collapse capacity is 29% lower when using the long duration set, as compared to the short duration set. For the concrete bridge pier, the collapse capacity is 17% lower. A comparison of commonly used duration metrics indicates that significant duration is the most suitable metric to characterize ground motion duration for structural analysis. Sensitivity analyses to structural model parameters indicate that structures with high deformation capacities and rapid rates of cyclic deterioration are the most sensitive to duration.

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