Performance-based earthquake engineering applied to a bridge in liquefied and laterally spreading ground.

P ERFORMANCE -B ASED E ARTHQUAKE E NGINEERING A PPLIED TO A B RIDGE IN L IQUEFIED AND L ATERALLY S PREADING G ROUND Scott J. Brandenberg 1) , and Pirooz Kashighandi 2) 1) Assistant Professor, Dept. of Civil and Env. Engineering, University of California, Los Angeles, United States 2) Graduate Student, Dept. of Civil and Env. Engineering, University of California, Los Angeles, United States sjbrandenberg@ucla.edu, pirooz@ucla.edu Abstract: Fragility functions developed for liquefaction and lateral spreading against typical classes of bridges are integrated with a probabilistic lateral spreading ground displacement methodology in a performance-based earthquake engineering example problem. A site near UCLA is selected and a probabilistic seismic hazard analysis is performed to obtain a hazard curve expressing mean annual rate of exceedance of peak ground acceleration. The disaggregation of the seismic hazard curve is also computed. A liquefiable soil profile is selected, and hazard curve expressing mean annual rate of non-exceedance of factor of safety against liquefaction is computed from the seismic hazard curve and disaggregation. A hazard curve expressing mean annual rate of exceedance of lateral spreading ground displacement is then computed using a semi-empirical probabilistic framework. The ground displacement hazard curve is compared with a typical approach wherein a probabilistic ground motion is selected and the engineering calculations are performed deterministically. Finally, the fragility functions are applied and a hazard curve is computed that expresses the mean annual rate of exceedance of various engineering demand parameters. This example problem shows how performance-based earthquake engineering can be applied to liquefaction problems to better communicate uncertainty and risk to decision- and policy- makers. 1. INTRODUCTION As of 2008, more than half of the earth's population lives in cities. Growth of our urban centers has placed a premium on sites with marginal or poor quality soils that had previously been considered inappropriate for development. This problem is particularly pertinent to geotechnical earthquake engineering because (1) a large fraction of the world's urban centers are in seismically active regions, (2) loose or soft soils have exhibited poor behavior due to cyclic failure and liquefaction in past earthquakes, causing death and billions of dollars in economic damages, and (3) our understanding of the seismic behavior of these soils is not well calibrated with meaningful experience because (thankfully) earthquakes are rare occurrences and few designers live to see how design-level shaking affects their projects. Geotechnical engineers strive to learn as much as possible from earthquakes as they occur around the world, but our evaluation procedures remain fraught with uncertainty. Considering how much uncertainty