Shear strengthening of RC beams with U-wrapped FRCM composites: assessment of current design guidelines

Fabric-reinforced cementitious matrix (FRCM) composites have been widely used in the past two decades as externally bonded (EB) reinforcement of existing concrete structures. They represent an effective solution for the flexural, shear, and torsional strengthening of reinforced concrete (RC) members. Shear strengthening with EB FRCM can be performed by either side bonding, U-wrapping, or full-wrapping the reinforcement around the cross-section of beams and columns. The FRCM can have a continuous or discontinuous layout, and the textile can be applied with different inclination angles with respect to the beam longitudinal axis. The contribution provided by the EB FRCM to the member shear strength is usually computed by an extension of the Mörsch truss model, which assumes the formation of a main diagonal shear crack. This approach is followed by both the Italian CNR-DT 215 (2018) and the American ACI 549.4R (2020) design guidelines, which provide similar formulations but rely on different hypotheses. In this paper, the accuracy of these formulations to determine the shear strength of U-wrapped FRCM-strengthened RC beams is assessed against a database of RC beams collected from the literature. Comparison between experimental results and analytical predictions allowed to identify the main features of the design models considered.