Amplitude-Scaled versus Spectrum-Matched Ground Motions for Seismic Performance Assessment

Abstract

The need to consider only a small number of ground motions combined with the complexities of response sensitivity to both modeling choices and ground motion variability calls for an assessment of current ground motion selection and modification methods used in seismic performance evaluation of structures. Since the largest source of uncertainty and variability arises from ground motion selection, this study examines the suitability of two ground motion modification (GMM) schemes: magnitude scaling (wherein the ground motion is uniformly scaled so that the resulting spectrum matches the amplitude of the design spectrum at the structural fundamental period) and spectrum matching. Comprehensive nonlinear time-history (NTH) simulations of two reinforced concrete moment frame buildings are carried out to evaluate the GMM approaches in the context of seismic demand prediction. Findings from the investigation indicate that spectrum matching is generally more stable than scaling both in terms of the bias as well as the resulting dispersion in the predicted demands. It is also concluded that seven ground motions are inadequate to establish median demands for taller frames where multiple modes influence structural response. Both methods are found to be sensitive to the choice of records for the cases investigated in this study.