Scaling Earthquake Ground Motion Records for Performance-Based Assessment of Buildings

摘要

The ATC-58 project is developing next-generation tools and guidelines for performance assessment of buildings, with a focus on measuring performance in terms of direct economic loss, casualties and downtime. The 35% draft of the Guidelines for Seismic Performance Assessment of Buildings presents procedures for intensity-, scenario- and time-based assessment using nonlinear dynamic analysis. Each assessment type requires the user to select and scale earthquake ground motions using procedures that are substantially different from those presented in current guidelines and codes of practice. For intensity-based assessment, a suite of ground motions is selected from bins of near-fault and far-field records (provided with the Guidelines) and scaled to a user-specified first mode period spectral acceleration. A suite of at least eleven ground motions is recommended to ensure that the median structural responses calculated by analysis are within 20% of the true median with approximately 75% confidence. For scenario-based assessment, a minimum of 11 target values of spectral acceleration are established using an attenuation relationship and a user-specified combination of earthquake moment magnitude and site-to-source distance. Seed ground motion records, consistent with the chosen magnitude and distance pair are selected and scaled to the target values, one seed ground motion for each target value. Two procedures are provided for time-based assessment, one that requires only the mean seismic hazard curve and another that uses the results of probabilistic seismic hazard analysis. Both procedures require the user to select and scale at least 11 earthquake ground motions at a minimum of 8 different intensities, each having an annual frequency of exceedance.