Independent seismic evaluation of the 24-580-980 south connector ramps response to the south connector ramps to a magnitude 7.25 Hayward Fault earthquake. Volume 3

The 24/580/980 interchange is located near Oakland California on the Eastern perimeter of the San Francisco Bay (Fig. 1 and Fig. 2). This interchange is a major artery in the Eastern San Francisco Bay area and provides a critical link between major bay area highways. The main Concord line of the Bay Area Rapid Transit System (BART), with ridership of approximately 270,000 per day, runs underneath the interchange. The interchange site is approximately 4 Km from the Hayward fault and 16 Km from the San Andreas fault. The reinforced concrete interchange was designed and constructed in the mid 1960`s and thus the asphalt structure has many of the vulnerabilities associated with typical pre-1970`s concrete structures (Roberts [1], Zefinski [2], Chai et. al. [3], Priestly and Seible [4]). In 1980 some of the seismic vulnerabilities were addressed as the interchange was retrofit with deck hinge restrainers as part of the California Department of Transportation (Caltrans) state-wide seismic retrofit of bridge expansion joints. The interchange was subjected to earthquake motion during the 1989 Loma Prieta earthquake and sustained minor damage in some of the concrete diaphragms which support the hinge restrainer forces [5]. Caltrans engineers, working together with their external consultants Imbsen and Associates, have recently completed a seismic retrofit design for portions of the interchange. The retrofit is primarily intended to fix inadequacies in many of the 1960`s vintage reinforced concrete elements which constitute the bridge superstructure and foundations.