Performance of Bridge Seismic Retrofits during Northridge Earthquake

After the 1989 Loma Prieta earthquake, California's Department of Transportation (Caltrans) began an ambitious program to screen, prioritize, and retrofit 2,000 seismically deficient California bridges. It was unfortunate that before this program was completed the Northridge, Calif., earthquake occurred. This paper summarizes how bridges with a post-1989 seismic retrofit performed during the 1994 Northridge earthquake. A description of typical retrofit details is given. A table provides data on all retrofitted bridges where ground motion exceeded 0.25g (where g= acceleration due to gravity) during the earthquake. Case studies of two retrofitted bridges that experienced ground motion of 0.50g are presented. There was no serious damage to any of these retrofitted bridges, although some were within 100 m of collapsed structures. Caltrans retrofits are designed to prevent collapse during the maximum credible earthquake. Bridge retrofit performance during the Northridge earthquake provides compelling evidence that these retrofits can achieve that goal.