SEISMIC RETROFITTING OF RECTANGULAR BRIDGE COLUMNS FOR SHEAR

Retrofitting measures applied to 2/5-scale shear-deficient columns representative of existing rectangular bridge columns in the Puget Sound area of Washington state were investigated. The retrofit methods studied included external hoops applied over the height of the column and full-height rectangular steel jacketing. Test specimens consisted of a single column connected at the base to a rectangular footing. The specimens were subjected to increasing levels of cycled inelastic displacements under constant axial load. Performance of the specimens was evaluated in terms of load capacity and ductility. Tests on the column representing as-built conditions resulted in a brittle shear failure at the calculated yield displacement, that is, at a displacement ductility level of mu = 1. Both retrofit methods investigated improved the behavior of the deficient column. With the external hoop retrofit, performance of the retrofitted columns was only moderately improved over that of the as-built column. Brittle fracture of the retrofit hoops limited the load-carrying capability and ductility enhancement, with displacement ductility levels of mu = 2 and 4 being achieved. With the use of the rectangular steel jacket retrofit, performance was significantly improved over that of the as-built column. The jacket retrofit resulted in a ductile column response with good load-carrying capability through mu = 8. Application of this retrofit over the full height of the column enabled the steel jacket to increase the column shear strength so that a flexural failure mode resulted. Although buckling of the steel jacket and longitudinal reinforcement occurred near the maximum moment section, sufficient confinement to the hinging region was provided by the buckled steel jacket to maintain load-carrying capability.