Forensic Investigation of Fire-Induced Collapse of a Steel Building

On May 23, 2020, a severe fire in a processing and storage steel structure located at Pier 45, Fisherman’s Wharf, in San Francisco, California, resulted in complete collapse of the single-story building. Accordingly, a post-fire forensic investigation was conducted to collect pre-fire and trans-fire event data, information regarding design of the structural system, and site observations of fire severity and structural failure. The collected information and engineering judgment was used to hypothesize a simplistic sequence of events leading to the fire-induced collapse of the building. To verify the hypothesized sequence of events, two distinct approaches were used to estimate gas temperature-time relations in a representative portion of the building, namely, standard fire exposure and zone-based compartment model. The generated gas temperature-time relations were utilized to predict temperature evolution in the column cross-sections using SAFIR software and then estimate failure time based on a critical temperature criterion. Material tests on steel coupons extracted from fire damaged members and thermo-mechanical modeling are planned in the future to further validate the hypothesized collapse mechanism.