Assessment of current nonlinear static procedures for seismic evaluation of buildings

An essential and critical component of evolving performance-based design methodologies is the accurate estimation of seismic demand parameters. Nonlinear static procedures (NSPs) are now widely used in engineering practice to predict seismic demands in building structures. While seismic demands using NSPs can be computed directly from a site-specific hazard spectrum, nonlinear time-history (NTH) analyses require an ensemble of ground motions and an associated probabilistic assessment to account for aleatoric variability in earthquake recordings. Despite this advantage, simplified versions of NSP based on invariant load patterns such as those recommended in ATC-40 and FEMA-356 have well-documented limitations in terms of their inability to account for higher mode effects and the modal variations resulting from inelastic behavior. Consequently, a number of enhanced pushover procedures that overcome many of these drawbacks have also been proposed. This paper investigates the effectiveness of several NSPs in predicting the salient response characteristics of typical steel and reinforced concrete (RC) buildings through comparison with benchmark responses obtained from a comprehensive set of NTH analyses. More importantly, to consider diverse ground motion characteristics, an array of time-series from ordinary far-fault records to near-fault motions having fling and forward directivity effects was employed. Results from the analytical study indicate that the Adaptive Modal Combination procedure predicted peak response measures such as inter-story drift and component plastic rotations more consistently than the other NSPs investigated in the study.