Experimental Investigation of an Appropriate Anchorage System for Flange-Bonded Carbon Fiber–Reinforced Polymers in Retrofitted RC Beam–Column Joints

Abstract

External application of fiber-reinforced polymers (FRPs) for the seismic retrofit/repair of reinforced concrete (RC) beam-column joints has been extensively investigated in the last decade. However, the majority of the suggested FRP schemes follow the application of the composite sheets on the webs of the beam and the joint core which would be impeded in real three-dimensional structures due to the presence of cross beams and slabs. In addition, upgrading code-compliant RC joints using a practical FRP scheme needs to be scrutinized in detail. A desirable retrofitting scheme for this type of joints may follow the application of composite sheets on the top and bottom sides (flanges) of the beam and columns aimed at increasing the flexural strength of beam-column joints. However, the major issue of concern for a flange-bonded FRP is providing adequate development length from the critical section to transfer the FRP tensile forces from beam to columns and vice versa. To overcome this concern, a novel anchorage system for flange-bonded carbon FRP (CFRP) is developed in this study and its efficiency is evaluated through a comprehensive experimental program. In total, nine small-scale (1/2.85) beam-column test specimens, including two control specimens, one damaged specimen, and six retrofitted specimens were considered. Both monotonic and cyclic loading regimes were implemented to estimate, albeit approximately, the seismic responses of the test specimens. The load-carrying capacity, initial stiffness, displacement ductility, and dissipated energy of beam-column joint subassemblies are compared before and after the application of the CFRP retrofits. The results showed a remarkable improvement in the load-carrying capacity and elastic stiffness of CFRP-retrofitted specimens, thus confirming the efficiency of the suggested anchorage system. In addition, and subject to specific circumstances, the plastic hinge can also be relocated away from the beam-column interface.