Behavior of carbon FRP strengthened T-connections under cyclic loading

This study is an investigation into the efficacy of using carbon fiber reinforced polymer sheets as a strengthening technique for reinforced concrete beam-column connections after circularizing the columns in the vicinity of the beams. Moreover, the consequences of applying multiple carbon fiber reinforced polymer layers rather than a single layer as external reinforcement for beam-column connections are explored. In this study, three identical beam-column connections were cast. One specimen was used as the control specimen while the other two were externally reinforced in the joint area with CFRP sheets. Prior to the application of CFRP sheets to the joints, the cross sections of the columns in the vicinity of the joints for two of the specimens were circularized by attaching concrete segments in order to eliminate sharp corners in the crosssection in order to put to the test the theory that the presence of sharp corners increases the concentration of stress in the CFRP reinforcement which in turn triggers early debonding of CFRP sheets. One of the strengthened specimens was reinforced with six times the number of CFRP layers used for the other strengthened specimen to investigate the effects of composite density on the final strength. The specimens were then placed under displacement control cyclic loading. The results of the tests confirmed the hypothesis that using CFRP composites as an external reinforcement technique for beam-column connections, significantly improves the performance of the joint under cyclic loading conditions. The ultimate strengths of the reinforced specimens were much higher than that of the control specimen and the strengthened specimens exhibited higher ductility than the control specimen. The results also suggested that the application of multiple CFRP layers enhanced joint ductility, ultimate strength and the overall performance of the specimens.