Probabilistic Evaluation of Seismic Performance of Vincent Thomas Bridge under Spatially Variable Ground Motions

The Vincent Thomas Bridge, a long span suspension bridge connecting the city of San Pedro and Terminal Island of Los Angeles Port, carries an overwhelming number of port traffic. Concerns regarding the seismic safety of the bridge have gained significant attention after the finding that the main span of the bridge lies directly over the Palos Verdes Fault, which has the capacity to produce an earthquake of magnitude 7.25 (M_w) with a return period of 1000 years. The bridge was thus retrofitted in spring 2000. In this study, a three dimensional finite element (FE) model of the Vincent Thomas Bridge are developed using a widely used software. In order to show the appropriateness of the model, eigenproperties of the bridge model are evaluated and compared with the results of system identification from ambient vibration and the 2008 Chino Hills earthquake response data. A new simulation technique is developed to generate spectrum-compatible spatial variable ground motions. The response of Vincent Thomas Bridge under spatially varying ground motion is evaluated by nonlinear time history analysis. Using spatially variable motions, it is found out that the response in some locations on the bridge deck, may be under predicted even if the motion with maximum intensity is uniformly applied at all supports. Therefore, to be more realistic in assessing the seismic performance of long span suspension bridge, the spatial variability of the ground motions should be considered in the analysis.