Using Collapse Risk Assessments to Inform Seismic Safety Policy for Older Concrete Buildings

Abstract

For many in the engineering community, nonductile concrete buildings are the next priority for seismic safety legislation in California. The history of such policies shows that implementation has been challenged by the high costs of seismic retrofit, opposition from building owners, and difficulty in defining and evaluating seismic safety standards. As a result, seismic legislation for existing buildings has developed in response to major earthquakes, rather than through proactive risk assessment. Advances in performance-based earthquake engineering provide a consistent framework for assessing building collapse risk using nonlinear dynamic analysis. These tools are applied to evaluate the risk of earthquake-induced collapse and fatalities in a representative set of older concrete frames. Results show that nonductile concrete frame buildings are about 35 times more likely to collapse in earthquakes than their modern counterparts. These assessments are used to investigate the impact of policy alternatives for seismic mitigation of nonductile concrete buildings.