Soffit and U-Wrap Fabric-Reinforced Cementitious Matrix Strengthening for Reinforced Concrete Beams

The structural performance of reinforced concrete (RC) beams strengthened with fabric-reinforced cementitious matrix (FROM) was investigated. Fourteen unstrengthened and strengthened beams were tested in flexure under four-point load configuration. Test parameters included the internal reinforcement ratios (0.5% representing flexure-deficient beams and 0.72 or 1.27% representing typical under-rein forced beams), the type of FRCM fabric (carbon and polyparaphenylene benzobisoxazole [PBO]), the number of fabric plies (one and two plies), and the strengthening scheme (straight at soffit or U-wrap). Test results revealed that the gain in flexural strength was inversely proportional to the internal reinforcement ratio of the beams regardless of the fabric type, scheme, or number of plies used. U-wrap strengthening scheme provided an inherent anchorage that limited the premature delamination of the fabric, which was a common mode of failure in the soffit-strengthening scheme. Beams strengthened with U-wrap single-ply of carbon- and PBO-FRCM showed an average gain in strength of 70% and 51%, respectively, compared to 28% and 20% for their counterparts strengthened with the soffit scheme. Moreover, the use of U-wrap double-ply of PBO fabric resulted in an average gain in strength of 72%. The theoretical formulations of ACI 549 satisfactorily predicted the load-carrying capacities of the soffit and U-wrap strengthened beams with an average ratio of P-u/P-u(Th) of 1.07 and a standard deviation of 11%.