Cyclic Evaluation of Severely Damaged RC Frames Repaired and Strengthened through FRP-Wrapped Coupler-Box Confinement

Abstract

The present study is focused on the retrofitting solution and its verification through experimental investigation for the two most common catastrophic modes of failure in reinforced concrete (RC) frame buildings, namely, buckling of reinforcing bars in the plastic hinge region of columns and shear failure of beam–column joints. The first mode of failure is retrofitted with interlinked coupler-box assemblies, while the second mode is repaired with external carbon fiber–reinforced polymer (CFRP) wrapping. The efficiency of the proposed retrofitting technique is evaluated by the hysteresis behavior, failure mechanism, and performance index parameters of the re-established frame, which are compared with the results of the initially tested bare frame. The recommended mechanism restricts the restored frame section against any possible movement or rotation and helps by a subsequent shift in yield location. The prime advantage of the proposed technique is that it prevents the possible slip of rebar from the sleeve, which is intercepted by the interlinking process, and eliminates the formation of inclined shear cracks at beam–column joints restricted by externally wrapped CFRP composites. The synergic effect of coupler-box and CFRP enhances the overall performance of the re-established frame by keeping the frame sections intact even after a lateral drift of 6%, which is relatively higher than the collapse prevention drift level, i.e., 4% as per FEMA guidelines. The obtained test results reveal the capability of CFRP and coupler-box assemblage as a possible futuristic approach for retrofitting outmoded RC building frames, in which buckling in longitudinal rebars of columns at their respective plastic hinge locations is inevitable.