Upgrading Bridge Outrigger Knee Joint Systems

摘要

A part of the joint Caltrans and University of California at Berkeley researchproject focused on the outrigger knee joint systems found in bents of elevated freeway bridges. Experiments on two half-scale as-built models confirmed the poor performance of existing outrigger knee joint systems observed after the 1989 Loma Prieta earthquake. Two seismic upgrading strategies, a 'ductile' and a 'strong' strategy, were proposed and tested on prototype specimens. The 'strong' strategy was chosen for the final seismic upgrade design. Two variations of the final design, one made using a post-tensioned reinforced concrete jacket, the other made using a steel jacket, were tested on three specimens. The seismic design guidelines, recommending the steel jacket upgrade, contain three parts: an upgrade design procedure based on capacity design principles; and energy balanced hysteresis model for dynamic analysis and tools for predicting or verifying the performance of the upgraded outrigger knee joints, developed in parallel with the experiments; and recommendations for detailing the steel jacket upgrade and a design example.