This paper describes the seismic retrofit program implemented bythe california department of transportation after the 1971 san fernando earthquake and accelerated after the 1989 loma prieta earthquake. The goal of the program is to reinforce most of the bridges designed and constructed prior to acquiring the current levels of knowledge of seismic loading and structure response (about 1978) to improvetheir structural ductility and resistance to the major factors which contributed to damage and collapse in the san fernando and loma prieta events. The program has been executed in two phases. The initial phase, completed in 1988, provided reinforcement to superstructures of 1260 bridges by connecting all narrow expansion joint seats with hinge restrainers and anchoring girders and other superstructure elements to the substructure. The single and multiple column retrofitphase, now under active implementation, is designed to reinforce substructure elements and create ductile members by increasing confinement. A risk analysis procedure was developed to prioritize the bridges for seismic upgrading so that highest risk bridges are retrofitted first. Legislation was recently enacted to require the departmentof transportation to also take the lead role in seismically retrofitting all locally owned bridges in the state. Research has been conducted, and is currently underway, at the university of california, san diego to test and confirm the validity of several proposed designsolutions for seismic retrofitting of existing bridge single columnbent substructure elements. Since the loma prieta earthquake additional research is being conducted at the university of california at berkeley, irvine and davis to develop and test retrofit techniques for multiple column bents and double level structures, including abutment and footing details. Some full scale testing was completed on astanding portion of the cypress street viaduct in oakland to determine its fundamental response characteristics and to test some techniques which may be applied to the double deck structures in san francisco and on complex structures with outrigger supports and other nonstandard support configurations throughout the state. This paper appears in transportation research record no. 1290, Third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 2.
Samenvatting