Evaluation of the Retrofitting Effect of a Building Based on FEMA P-58’s Quantitative Method and EPRS Rating Criteria

Structural retrofitting targets to improve seismic performance of a building, however, it might be difficult for structural engineers to demonstrate and persuade building owners that the retrofitting is cost efficient without experiencing or at least expecting a real earthquake. There are three main reasons that contribute to this. First, earthquakes, as well as structure seismic responses, are random process in both time-wise and intensity-wise. It is difficult for engineers to explain the deterministic structural design or analysis results to non-engineering people, given the uncertainty nature of earthquakes. Second, owners are more interested in the fiscal loss or fiscally related issues, such as injury or usage down time, while engineers only focus on structural behavior. Third, once the minimum requirement in building code is met, there is no more incentive for owners to spend money in their structures. In recent years, there are great efforts to advocate performance based earthquake engineering (PBEE) and more resilient structures. Two of them are the FEMA P-58 project and SEAONC’s EPRS. FEMA P-58 (by FEMA and ATC) provides methodology for probabilistic structure seismic analysis and tools for estimating the monetary loss and down time. EPRS is a rating system of building seismic safety, repair and recovery, and it has already been adopted by Los Angeles City. Predictably, it assists local authorities to request retrofit on buildings and it may impact building seismic insurances rates. This study utilizes FEMA P-58 and EPRS to evaluate retrofit of a building selected from SAC Steel project. It demonstrates that FEMA P-58 is helpful for incorporating probability into the structural analysis and correlating the structure’s performance and fiscal loss. The benefit of retrofit can be demonstrated by the criteria either in FEMA P-58 or EPRS.