Strengthening of Shear Deficient Reinforced Concrete Beams using Anchored CFRP sheets

Abstract

Fiber-reinforced polymer (FRP) composite materials have been widely implemented to strengthen existing reinforced concrete (RC) structures in the past three decades. Studies have shown that externally bonding FRP materials to concrete substrate has proven to be effective in enhancing the shear capacity of RC beams. However, premature debonding of FRP laminates prevents the beam’s ability to utilize the laminates’ strength, and typically fail in a brittle mode. For this purpose, the current research aims to study the effect of anchoring CFRP laminates with CFRP splay anchors to strengthen RC T-beams in shear. The CFRP anchors are expected to delay or prevent debonding of the CFRP laminates, especially when the web of T-beams is shallow. There is still a gap in the available literature directed to the effect of FRP anchors on the strength and ductility of RC beams externally strengthened in shear with CFRP laminates. In addition, there are no design guidelines in the current codes of practice for strengthening with FRP anchors. Accordingly, a total of fifteen shear deficient T-beams were cast and externally strengthened with CFRP sheets in the form of U-Wraps and anchored with different configurations of CFRP splay anchor systems. The variables of the experimental program are anchor embedment depth, dowel diameter, insertion angle, and fan length. In addition, placing of the anchors before the U-wraps is investigated. The performance of the anchored U-wrapped specimens in terms of failure modes, load-deflection responses, shear strength, strain in CFRP laminates, and ductility is compared to that of unstrengthened and unanchored strengthened control specimens. Test results showed that CFRP anchors delayed debonding of the U-wraps, improved the shear strength of unanchored U-wraps by 14- 52%, and significantly enhanced the ductility of the beam specimens. It was concluded that bonding CFRP laminates by well-designed CFRP anchors highly utilized the strain attained in CFRP laminates. In addition, the FRP shear contribution is predicted using the ACI440.2R-17, CSA-S806.12(R2017), fib-14, and ISIS-M04 guidelines. Based on comparison with the experimental results, the ACI440.2R-17 and CSAS806.12(R2017) shear provisions provide reasonable predictions provided that the effective strain in CFRP laminates is limited to a value of 0.004.