An Ounce of Prevention: Probabilistic Loss Estimation for Performance-Based Earthquake Engineering

Abstract

Performance-based earthquake engineering (PBEE) is a methodology that incorporates desired performance levels into the design process. Performance in PBEE can be expressed in economic terms, or as elapsed downtime, or in terms of life and building safety objectives. These performance objectives are relevant to various types of stakeholders. They should be addressed in building loss estimation procedures because after an earthquake, the repair cost will not be the only "loss" suffered by building stakeholders. In a sizeable earthquake, there will likely also be some losses due to business interruption during the repair effort, building closure taken as a post-earthquake safety precaution, and human casualties caused by building failures during the seismic event. An analytical approach for PBEE is developed and implemented to evaluate the performance of a new reinforced-concrete moment-frame office building. The PBEE approach used is consistent with the Pacific Earthquake Engineering Research (PEER) center's modular framework, which is divided into four core analytical stages: hazard analysis, structural analysis, damage analysis, and loss analysis. Future losses of the building are uncertain because they depend on uncertain quantities, such as the shaking intensity of the earthquake, the mechanical properties of the facility, and the uncertain damageability and unit repair costs of the facility. An analytical approach is developed to propagate these uncertainties. This work presents the mathematical foundation for the damage and loss analyses, and a description of its implementation into software. The results from running this software on multiple design variants of the building are presented, viii including seismic vulnerabilities as a function of shaking intensity and corresponding expected annual losses. The methodology developed and implemented in this work estimates the direct economic losses due to repair costs as well as two types of indirect economic losses, those produced by building downtime and by human fatalities. A procedure for a virtual inspection is used to assess the safety of buildings, based on current damage assessment guidelines. Additionally, a model is established to estimate human fatalities caused by the partial and global collapse of buildings, using probabilities of fatality based on relevant empirical data and the results of the virtual inspection process. A simplified methodology is presented for estimating building downtime after seismic events, including mobilization delays before construction begins and the elapsed time needed to repair damaged building components. The losses due to downtime and human fatalities are then added to the building repair cost in order to estimate the total building loss, which is then used to perform a benefit-cost analysis of the benchmark building. The work presented, is to our knowledge, the most faithful attempt to estimate the main decision variables (termed the 3 Ds-dollars, deaths, and downtime), proposed by PEER and the ATC-58 Project for performance assessment of structures.