Cyclic Response of Rectangular RC Columns with Bond-Damaged Zones Repaired Using Steel or CFRP Confinement

Abstract

The results of an experimental investigation that was under taken for evaluating the cyclic lateral load-drift response of rectangular reinforced concrete (RC) columns that were damaged due to large drift reversals, but then repaired for upgrading the bond strength of the spliced reinforcement within the critical hinging region are presented in this paper. The original specimens consisted of full-scale unconfined and fiber-reinforced polymer (FRP) confined columns having a relatively high section aspect ratio of 2.0. These original specimens were subjected to large drift reversals until complete bond degradation of the spliced reinforcement within the hinging zone and complete loss of flexural strength of the columns. The repair procedure consisted of removing the deteriorated concrete within the damaged/splice zone and casting new concrete. Two types of concrete confinement for improving the bond strength and flexural capacity were investigated and compared, namely, internal confinement by transverse steel ties and external confinement using carbon fiber-reinforced polymer (CFRP) jackets. It was found that repairing the bond-damaged zone through concrete confinement leads to substantial regain of flexural strength up to or exceeding the strength of the original specimens, lower structural damage associated with concrete fracturing and bond degradation, and considerable improvement of the energy dissipation capacity under cyclic loading. Confinement by external FRP jackets was relatively more effective than confinement by internal steel ties. However, unlike columns with continuous reinforcement, columns with spliced reinforcement within the hinging region experienced significant bond and strength degradation beyond drift ratios between 3 and 4%, irrespective of the type and amount of confinement used. The experimental results are discussed, and a design expression for estimating the thickness of the FRP jacket required for seismic bond strengthening is presented and compared with the test data.