Current Seismic Soil-Foundation-Structure Interaction State of the Art and Practice on California Toll Bridge Program

California Department of Transportation (CALTRANS) initiated a seismic retrofit program in early 1990 following the Loma Prieta and Northridge Earthquakes to strengthen existing toll bridges and many regular bridges in California. Prior to the CALTRANS’ seismic retrofit program, there were very little guidelines and criteria available to undertake seismic retrofit of existing bridges and design of new structures to withstand potentially large magnitude future earthquakes. Significant advancements have been made since the beginning of the seismic retrofit program. This paper will discuss the author’s experience from the seismic retrofits of many existing toll bridges and designs of new toll bridges. The lessons learnt from the seismic retrofit program paved the way for the designs of new major bridges, including East Span San Francisco – Oakland Bay Bridge, New Carquinez Bridge, New Benicia – Martinez Bridge, and New Gerald Desmond Bridge. In the areas of seismology, many advances have been made following the measurements of strong motion earthquakes in Turkey and Taiwan, which have significant impact on establishment of ground motion criteria for recent major bridge projects. Site response and soil-foundation-structure interaction (SFSI) analyses have been improved over the last decade since the first seismic retrofit was undertaken