Behavior of Bridge Outrigger Knee Joint Systems

The catastrophic collapse of the Cypress Street Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of older elevated freeway bridge structures. One part of a joint Caltrans/University of California at Berkeley research project is the investigation of outrigger knee joints found in elevated freeway bents. This project has two principal goals: to evaluate the behavior of the existing outrigger knee joint systems under a combined transverse and longitudinal loading, and to design and experimentally verify upgrading strategies and repair techniques suitable for application on the existing elevated freeways. The primary focus of this paper will be to present the behavior of the as-built and upgraded systems, but an overview of the design method and the analytical tools used in the upgrade will also be presented.