Shear Retrofitting of Corner 3D-Reinforced Concrete Beam-Column Joints Using Externally Bonded CFRP Reinforcement on Grooves

Abstract

Beam-column joints are fundamental structural components to provide stability to a concrete frame. Compared to other types of joint, corner joints are more susceptible to failure due to their smaller size and inferior confinement; therefore, it is necessary to develop efficient techniques for strengthening three-dimensional (3D) corner deficient joints of reinforced concrete (RC) structures. However, most research has focused on two-dimensional (2D) joints due to the complexity of casting and testing 3D ones. Moreover, the effect of lateral beams on the confinement of the joint zone has been neglected in most cases. These shortcomings undermine the applicability of some of the retrofitting configurations proposed so far to real 3D structures. This study investigates the shear strengthening of nonseismic 3D corner joints, i.e., those lacking adequate transverse reinforcement in the joint zone, using carbon fiber reinforced polymer (CFRP) sheets. To delay the debonding of CFRP sheets off the concrete substrate, the externally bonded reinforcement on groove (EBROG) technique is used, and the hysteretic response of 3D corner joints strengthened via the EBROG method is analyzed. Five 3D joint specimens in half-scale size were manufactured and tested. The specimens consisted of one control specimen, one standard specimen conforming to code requirements, and three FRP-retrofitted specimens with L-shaped strengthening configurations. Results indicated that the adopted strengthening configurations prevented the shear failure of the joint. Furthermore, the EBROG method enhanced the load-carrying capacity and ductility of the RC joints by up to 38 and 69% respectively, compared with the control specimen. Comparison of the maximum loads achieved at a drift ratio of 4.5% revealed that the EBROG technique combined with CFRP fans prevented any load reduction up to the test termination.