The Continuing Challenge: Report on the Performance of State Bridges in the Northridge Earthquake

Abstract

Bridges affected by the Northridge earthquake were examined to evaluate the performance of Caltrans bridges, retrofit and peer review programs, and technical procedures. All structures in the region of strong shaking that had been retrofitted since 1989 performed adequately; if the seven bridges that collapsed had been retrofitted, they would be expected to have survived with little damage. The bridges subjected to strong shaking that had been constructed or retrofitted to current Caltrans criteria had, at most, minor damage; all remained in service. The Seismic Advisory Board concluded that the Caltrans seismic design procedures for new bridges and its retrofit procedures for existing hazardous bridges are technically sound. The Board found that the retrofit program is proceeding fairly well, but that the screening methods used to identify hazardous bridges could be improved as could the pace of retrofitting, particularly toll bridges. There were no construction projects underway in the Spring of 1994 for toll bridges, nor had preparation of retrofit designs begun. Twenty-one findings and seventeen recommendations are presented. Although much has been accomplished, much remains to be done. With some improvements, the Caltrans program should be continued with dispatch and determination. The major foreseeable impediments to a successful program are inadequate or fluctuating funding. The Seismic Advisory Board has confidence that the California highway system is progressing in an orderly fashion to one that is significantly more seismically safe.

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