Benchmarking FEMA P-58 repair costs and unsafe placards for the Northridge Earthquake: Implications for performance-based earthquake engineering

Performance-based earthquake engineering organizes the explicit quantification of building seismic performance and risk, facilitating risk-informed design and mitigation decisions. However, little work has been done to benchmark outcomes from these procedures with the available empirical evidence from past earthquakes. In this study, we benchmark the end-to-end outcomes of the FEMA P-58 performance-based engineering methodology against empirical data from California?s 1994 Northridge Earthquake. Specifically, we perform a regional scenario assessment for around 2.6 million buildings in the Los Angeles area at the time of the 1994 earthquake to hindcast repair costs and numbers of unsafe placards from the earthquake. Based on the initial comparison with losses from the Northridge earthquake, we find expected values from our FEMA P-58 regional assessment to overpredict repair costs and unsafe placards, especially for wood frame buildings at low-to-moderate levels of shaking. We use this comparison to investigate underlying methodological and modeling assumptions and propose procedures to improve the outcomes, including increasing elastic damping for wood buildings, updating the FEMA P-58 virtual inspection process for unsafe placarding, and adopting truncated fragility functions to define uncertainties in damage. Outcomes from the proposed methodological updates provide a close match to observed losses in terms of repair costs and numbers of unsafe placards from the event for most building types.