Stress transferred at the main shear crack of reinforced concrete beams strengthened with U-wrapped inorganic-matrix composites

Shear strengthening of existing reinforced concrete (RC) members is nowadays often performed using externally bonded reinforcement (EBR) comprising inorganic-matrix composites, such as fiber-reinforced cementitious matrix (FRCM) (also referred to as textile reinforced mortar, TRM) and textile reinforced concrete (TRC) composites. They can be either side-bonded to, U-wrapped around, or fully wrapped around the cross-section of beams and columns. When U-wrapped FRCMs are employed in the shear strengthening of RC beams, failure of the EBR is usually due to FRCM debonding (triggered by the opening of shear cracks along the shear span) rather than to the attainment of the composite tensile strength. The contribution provided by the EB composite to the member shear strength is usually computed by an extension of the Mörsch truss model, which assumes that most of the stress borne by the composite is transferred across a main diagonal shear crack. Accordingly, the composite shear strength contribution is evaluated starting from the axial (i.e., fiber-aligned) stresses in the FRCM strips crossing the main shear crack. Hence, the study of the stress-transfer mechanism in the FRCM strips bridging the shear crack is of paramount importance to guarantee a reliable estimation of the composite shear strength contribution. In this paper, an analytical approach is proposed to describe the distribution of stresses developing in the FRCM shear reinforcement. The results provide an accurate description of the stress transferred at the main shear crack, which in turn allows for an accurate estimation of the composite shear strength contribution.