Directivity-Induced Pulse-Like Ground Motions and Fracture Risk of Pre-Northridge Welded Column Splices

Abstract

ABSTRACT Recent worldwide earthquakes have emphasized the severe damage potential of pulse-like ground motions caused by forward directivity close to a fault rupture. We investigate the effect of such directivity-induced pulse-like ground motions on the fracture fragility and fracture risk of pre-Northridge welded column splices (WCSs) in near-fault regions. To this aim, incremental dynamic analysis (IDA) is employed to explicitly quantify the pulse effects on WCS stress demands. Two case-study nonlinear welded-steel-moment-resisting-frame (WSMRF) models featuring WCSs (i.e., 4 and 20 story) are developed and subjected to (1) a set of pulse-like ground motions with varying pulse periods; and (2) a suite of ordinary (i.e., non-pulse-like) ground motions. Fracture fragility curves for both ordinary and pulse-like records are then derived from the IDA results. These are finally combined with state-of-the-art near-source probabilistic seismic hazard analysis (NS-PSHA) for a case-study scenario rupture and six representative near-fault sites to assess WCS fracture risk. Findings from the study highlight that directivity-induced pulse-like ground motions affect the estimated fracture fragility and potentially increase the fracture risk of pre-Northridge WCSs in near-fault regions. These findings can guide similar performance-based assessment exercises for WSMRFs to inform, for instance, the planning and design of retrofitting strategies for those vulnerable connections in near-fault regions.