The Earthquake Engineering Online Archive

Upgrading bridge outrigger knee joint systems

Stojadinovic, Bozidar; Thewalt, Christopher R.

UCB/EERC-95/03, Earthquake Engineering Research Center, University of California, Berkeley, 1995-06, 167 pages (630/S764/1995)

The collapse of the Cypress Street Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of elevated freeway bridge structures. A part of the joint Caltrans and University of California at Berkeley research project, initiated after the earthquake, focused on the outrigger knee joint systems found in bents of elevated freeway bridges. The investigation had two principal goals: to evaluate the behavior of the existing outrigger knee joint systems under a combined transverse and longitudinal loading and to devise and experimentally verify strategies for seismic upgrading of existing outrigger knee joints. Experiments were conducted on two half-scale as-built models. Two seismic upgrading strategies, a "ductile" and a "strong" strategy, were proposed and tested on prototype specimens. The ductile strategy improves the system by distributing the energy dissipation to plastic hinges in the beam and in the column. The strong strategy concentrates yielding in the column hinge. 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 upgrade design guidelines, recommending the steel jacket upgrade, are presented.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-95-03.pdf (16 MB)