Metamodel-based regional vulnerability estimate of irregular steel moment-frame structures subjected to earthquake events

Rapid seismic vulnerability assessment tools for use with existing structures not only help in quantifying their susceptibility to structural failure, but also aid decision makers with regional portfolio earthquake risk mitigation. Steel moment-frame structures are a common structure type in the United States, and most research to date on their regional assessment has focused on the fragility analysis of structures with regular configurations. Given the large number of irregular structures in use in seismically active zones, the effect of plan-form irregularity on the fragility of moment-frame structures should be examined. The focus of this study is to estimate structural fragilities for the class of L-shaped steel moment-frame (LSMF) structures in the Central United States. As part of the assessment process, L-shaped plan-forms that are most common in the region are first selected based upon input from structural and architectural experts. Significant parameters affecting the LSMF seismic responses are identified from sensitivity studies using finite element models and design-of-experiments methods to construct response surface metamodels (RSMs). Portfolio-level fragility curves for LSMF structures are generated from the RSMs joined with Monte Carlo Simulation (MCS) to treat regional uncertainty. RSM-based fragility curves are also compared with fragilities from HAzards US Multi-Hazard (HAZUS-MH). Furthermore, a fragility-based parametric study is performed to evaluate the effect of significant parameters on LSMF susceptibility. Findings indicate the extent to which different irregularity parameters such as first floor height and eccentricity impact regional LSMF vulnerability.