Shear Strength Model for RC Beams with U-Wrapped FRCM Composites

The shear strength of reinforced concrete (RC) elements can be improved by applying externally bonded (EB) fiber-reinforced cementitious matrix (FRCM) composites. FRCM composites are generally U-wrapped around the cross-section of RC beams and completely wrapped around the cross-section of RC columns. When the U-wrapped layout is employed, composite debonding usually occurs before the tensile strength of the composite can be attained. However, depending on the specific FRCM adopted, different failure modes can be observed. Although the use of FRCM composites to strengthen existing RC members is gaining popularity, limited work has been done to formulate a reliable design procedure for FRCM shear strengthening of RC members. In this paper, a model is proposed to compute the shear strength contribution of FRCM composite U-wrapped around RC members. The model, which is an extension of the model used for fiber-reinforced polymer (FRP) shear strengthened beams, is based on mechanical considerations, does not contain empirical coefficients, and can be applied to any FRCM composite provided that the bond behavior and tensile strength are identified. The model is validated by comparing the analytical predictions with the experimental results of RC beams strengthened in shear with polyparaphenylene benzobisoxazole (PBO) and carbon FRCM composites found in the literature. Finally, an example of the evaluation of the shear capacity associated with the FRCM reinforcement is provided to illustrate the use of the model.