Strengthening RC beams with circular post-opening in shear zone by externally bonded CFRP

An installation of post-drilled openings in existing reinforced concrete (RC) beams may result in an abrupt change in the beam’s cross-sectional dimensions, which could reduce the beam’s capacity and integrity of the beam. A variety of methods have been developed to adequately reinforce the area around the opening. This study investigates the efficacy of Carbon Fibre Reinforced Polymer (CFRP) sheets for strengthening RC beams with circular post-opening at shear zones. A total of five beams measuring 150 mm width, 300 mm depth and 1550 mm length were casted and tested under four-point load until failure. The beams were consisted of one solid beam used as a control beam, two beams having 100 mm diameter circular openings and another two beams were strengthened using externally bonded CFRP sheets around the openings. The ultimate load capacities, deflections, strain distributions, cracking propagation and failure modes of the tested beams were measured and compared. According to the test results, beams with openings had lower load capacity and less stiffness compared to solid beam. Increasing the number of openings significantly reduced the ultimate load of the beams up to 25%. There are also significant differences between beams without and with strengthening in terms of beam capacity, stiffness and strain distribution.