Accounting for Ground-Motion Spectral Shape Characteristics in Structural Collapse Assessment through an Adjustment for Epsilon

Abstract

One of the challenges of assessing structural collapse performance is the appropriate selection of ground motions for use in the nonlinear dynamic collapse simulation. The ground motions should represent characteristics of extreme ground motions that exceed the ground-motion intensities considered in the original building design. For modern buildings in the western United States, ground motions that cause collapse are expected to be rare high-intensity motions associated with a large magnitude earthquake. Recent research has shown that rare high-intensity ground motions have a peaked spectral shape that should be considered in ground-motion selection and scaling. One method to account for this spectral shape effect is through the selection of a set of ground motions that is specific to the building’s fundamental period and the site hazard characteristics. This selection presents a significant challenge when assessing the collapse capacity of a large number of buildings or for developing systematic procedures because it implies the need to assemble specific ground-motion sets for each building. This paper proposes an alternative method, whereby a general set of far-field ground motions is used for collapse simulation, and the resulting collapse capacity is adjusted to account for the spectral shape effects that are not reflected in the ground-motion selection. The simplified method is compared with the more direct record selection strategy, and results of the two approaches show good agreement.