Seismic Vulnerability Assessment of Steel Moment-Resisting Frames Based on Local Damage

This paper investigates the seismic vulnerability of steel moment-resisting frames (SMRFs) based on plasticity development in structural components. Pushover analyses with three different lateral load patterns are performed to identify the location of plastic hinges at the collapse state and IDA analysis is employed to find the seismic intensities causing the formation of the specified hinges. An ensemble of 30 near-fault pulse-like motions classified into three groups of short, medium and long period motions and ten ordinary ground motions are used for seismic loading on five sample frames with 3 to 15 stories. Employing this method, the interstory drift ratio coincident to the seismic collapse is evaluated. Then, the critical pulse period producing the most damage to the structures is estimated. Finally, fragility curves are developed for near- and far-fault excitations. The results indicate that maximum interstory drift ratio at the collapse state of the frames ranges from 1.5% to 10%. It is also found that the ratio of critical pulse period to natural period of SMRF structures is between 2.3 and 2.9. Moreover, the fragility analysis reveals that collapse intensity equivalent to 10% of exceedence for near-fault motions is 70% to 85% less than far-fault records.