Experimental Evaluation of Steel Bracings and Metallic Yield Damper as Retrofit Techniques for Severely Damaged RC Building Frames

Abstract

ABSTRACT The concentrically placed hollow circular steel bracings and hybrid metallic yield dampers as structural retrofitting techniques for severely damaged reinforced concrete (RC) portal frames are evaluated under reverse-cyclic load conditions. In addition, the efficiency of a specially designed coupler-box assembly to retrofit severely damaged columns of the model frame by reconnecting the buckled or ruptured longitudinal reinforcing bars at the plastic hinge locations is evaluated under similar load conditions. Competency of the proposed techniques is assessed by comparing the hysteresis behavior, performance index parameters, and failure mechanism of the retrofitted frames with the native-tested conventional bare frame. The lateral load and deformation capacities are significantly enhanced in the retrofitted frames with a comprehensive increase of 2.0 times in the braced frame and 2.5 times in the damper-equipped frame compared to the conventional bare frame. A stable and symmetric post-yield behavior is noticed in the retrofitted frames until a lateral drift of 3.5% and 6% in braced and damper-fit frames, respectively, which is even higher than the collapse prevention drift level specified in FEMA codal guidelines.