Evaluation of the contribution of flexural CFRP plates in shear strengthening RC beams

Abstract

Strengthening of RC beams for shear has been typically done by externally attaching strips of steel plates or carbon-fiber reinforced polymer (CFRP) sheets or plates on the sides of the beams. However, sides of beams deficient in shear may not be always accessible for such a strengthening technique. The objective of this pilot study is to investigate the effectiveness of externally bonded CFRP flexural reinforcement to improve the shear strength of beams and to quantify their contributions. A pilot test was conducted which included three beam specimens. All beams were reinforced with 2[phi]12 steel bars (approximately 1% reinforcement ratio) and were casted without transverse reinforcement in their shear span. Two beams were strengthened with one and two layers of CFRP plates as external flexural reinforcement while the third beam was left as the control specimen. The beams were tested under four-point loading. Load and mid-span deflection readings were recorded until failure. All specimens failed in shear as a result of a diagonal-tension crack. The strengthened specimens with one and two layers of CFRP plates showed an increase in their shear capacity of 55% and 76%, respectively, over the control specimen. It was concluded that CFRP plates, when externally bonded to the soffit of simply supported beams, enhance both flexural and shear capacity of such beams. As a result, a comprehensive testing program is now underway. Specimens will be tested by varying the steel reinforcement ratio, the CFRP reinforcement ratio, and CFRP plates vs. sheets, in an effort to quantify the contribution of flexural CFRP reinforcement in shear strengthening of RC beams.