Seismic Loss Assessment of Existing Tall Stell Buildings in Los Angeles

There is a renewed and growing interest on seismic performance of the existing tall- building stock in Los Angeles during a major seismic event. Of particular interest is the seismic performance of existing high-rise buildings constructed before the 1994 Northridge Earthquake. These buildings have been designed without the help of the state-of-the-art nonlinear analysis methodologies and recently published performance based seismic design guidelines (PEER, 2010; LATBSDC, 2014), and have been known to contain defects in the welded beam-to-column connections rendering them susceptible to large earthquakes

This study involves nonlinear modeling of a 24-story existing steel building in Los Angeles. The building has been analysed under 7 two-component horizontal ground motions and a retrofit scheme is proposed based on the observed deficiencies. Seismic performances of the existing and the retrofitted buildings are compared, and loss estimation analyses are conducted using FEMA P-58 methodology and the PACT (Performance Assessment Calculation Tool) (Naeim et. al., 2007) software. Results indicate that repair cost, downtime and probability of getting unsafe placard after an earthquake can substantially be reduced by the proposed retrofit scheme. Further analyses results and the accompanying seismic strengthening studies will provide a wider picture of the region-wide impact of the next major earthquake and aid in reinforcing city of Los Angeles’s vision of increasing seismic resiliency in its disaster mitigation plans.