Inadequate flexural strength and ductility of shear strength of concrete bridge columns has resulted in collapse or severe damage ofa number of california bridges in recent moderate earthquakes. In general these bridges were designed prior to the new seismic design methods which were implemented in the mid-seventies. Bridges constructed in accordance with the new design methods have performed well in recent earthquakes. However, the large number of older bridges that are in service, particularly freeway overpasses designed and constructed in the 1950's to 1970's, are now recognized to have substandard design details and are presenting a cause for major concern. Thispaper reports the results of a theoretical and experimental programinvestigating retrofit techniques for circular columns by encasing the critical regions with a steel jacket. The jacket is bonded to the column using grout. Results from six large-scale column tests showthat the casing acts efficiently as confinement reinforcement enabling displacement ductility factor of greater than 6 to be achieved. The casing also inhibits bond failures at the laps of longitudinal reinforcement in the critical regions of the column by restraining the dilation and spalling of the cover concrete which degenerates intobond failure. Coparisons of "as-built" and retrofitted columns arepresented, and experimental strengths and ductilities are compared with analytical predictions. This paper appears in transportation research record no. 1290, Third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 2.
Abstract