SEISMIC RETROFIT OF CIRCULAR BRIDGE COLUMNS FOR ENHANCED FLEXURAL PERFORMANCE

Collapse or severe damage of a number of California bridges in recent moderate earthquakes has emphasized the need to develop retrofit measures to enhance flexural strength, ductility, and shear strength of bridge columns designed before current seismic design provisions were implemented. This paper reports results of a research program investigating the retrofit of circular columns by encasing plastic hinge regions with a bonded steel jacket. Results from six large-scale column tests showed that steel jacketing results in column ductilities as high as those available from confined columns designed to current codes, and inhibits bond failures in lap splices of longitudinal reinforcement in plastic hinge regions. A secondary result from the tests was the identification of joint shear failure at the footing/column junction as a potential failure mechanism for old and current footing designs.