Shear Strengthening of Reinforced Concrete T-Beams with Anchored CFRP Laminates

Abstract

Strengthening of existing reinforced concrete (RC) structures by externally bonding carbon fiber–reinforced polymers (CFRP) applied to the concrete substrate has proven to be effective in enhancing the shear capacity of RC beams. However, a premature debonding of CFRP laminates does not allow a full utilization of the strength of laminates. This paper reports on a research program that aimed at studying the effect of anchoring CFRP sheets used for shear strengthening using CFRP splay anchors. The anchors were used to further improve the shear strength contribution of FRP by delaying debonding and achieving a higher strain in the external CFRP reinforcement. A total of nine shear-deficient T-beams were cast and externally strengthened with high-modulus CFRP laminates in the form of U-wraps and anchored with different configurations of high-modulus CFRP splay anchors. The variables considered for the experimental program included anchor embedment depth and anchor splay length. In addition, the effect of installing the anchors directly on the concrete substrate prior to installing the U-wraps was investigated. The performance of the anchored U-wrapped specimens in terms of failure modes, load–deflection responses, and shear strength and strain in CFRP laminates was compared with that of unstrengthened and unanchored strengthened control specimens. The test results showed that high-modulus CFRP anchors delayed the debonding of the U-wraps and significantly improved the shear strength and ductility of the beam specimens. It was also concluded that anchoring CFRP U-wrap shear reinforcement by properly designed CFRP anchors allows for a higher strain to be attained in the CFRP laminates. A comparison between the experimental capacities of the tested specimens with the theoretical values predicted using current standards provides reasonable predictions on the shear capacity of anchored specimens.