Caltrans Seismic Retrofit Program after the 1971 San Fernando Earthquake

Prior to the February 9, 1971, California’s Department of Transportation (Caltrans) bridges were designed with very limited seismic design criteria. Consequently, several bridges and interchanges were severely damaged during the San Fernando earthquake. Within a few days after the earthquake, Caltrans managers had written change orders that all bridges under construction were required to have much more transverse reinforcement in the columns, end the practice of using undeveloped starter bars between foundations and columns, and increase seat lengths to at least 18 in.; all to prevent the types of damage that was observed after the earthquake. However, at that time the interstate highway system was almost completely built. Consequently, most of California’s bridge inventory had been designed with little resistance to large earthquakes. Caltrans has been playing catch-up ever since, retrofitting and re-retrofitting vulnerable bridges as new lessons were learned after every earthquake.