Experimental Investigation on Shear Strengthening of RC Cantilever Beams with External Steel Plates

Abstract

Shear strengthening of reinforced concrete (RC) beams has been widely investigated using simply supported beams; however, such tests may not be fully representative of real structural elements such as cantilever beams. Therefore, this study experimentally evaluates the effectiveness of externally bonded steel plates for shear strengthening of RC cantilever beams. Three reinforced concrete double-overhanging beams with identical geometry, the same shear span-to-effective depth ratio (a/d = 2.45), and the same longitudinal top reinforcement ratio (ρ = 1.28%) were tested without stirrups, providing six shear tests (two per beam). One test served as a control, while the remaining tests were strengthened using externally bonded steel plates with a thickness of 1.50 mm. The variables included the steel-plate shape (vertical strips, 45° inclined strips, and a continuous horizontal plate covering the shear span), and the method of fixing the steel plates to the concrete surface (Sikadur 31-CF epoxy adhesive, with or without mechanical anchorage). All beams were loaded by a single concentrated load applied at the cantilever tip, and crack propagation, deflections, and steel strains were recorded to establish load-deflection and load-strain relationships. The results showed that all strengthening techniques enhanced the shear capacity and, in some cases, shifted the failure mode from shear to shear-tension; the most effective technique was the continuous steel plate bonded using adhesive only, achieving a 68% increase in shear strength compared with the control beam. The experimental results were compared with analytical formulas and design code provisions. The comparison indicated that the formula proposed by Alam and Al-Amin provided the best predictions for steel strip-strengthened beams, while the formulas by Sharif et al. and Barnes and Mays showed the closest agreement for steel plate-strengthened beams.