MODELLING SHEAR MECHANISMS IN FRP-STRENGTHENED R/C BEAMS

An extended experimental work was performed, aimed at obtaining a clear understanding of the underlying mechanisms of the shear strengthening of reinforced concrete beams with fibre reinforced polymers (FRP) and an analytical model was developed, in order to reproduce rationally their features. Analytical expressions of the stress field in the FRP sheet crossing a shear crack are obtained, through the definition of: (i) the generalised constitutive law of a bonded FRP sheet, of (ii) the compatibility required by the shear crack opening, and of (iii) the appropriate boundary conditions depending on the strengthening configuration. These expressions allow for an easy definition of closed-form equations for the effective resistance of the strengthening by FRP strips or sheets used for shear, as function of the adopted strengthening configuration and of some basic geometric and mechanical parameters. The contribution of the strengthening FRP is then added to those of concrete and reinforcing steel, adequately weighed. The model’s accuracy has been verified through correlation studies with experimental results, obtained from the literature and from laboratory tests on purposely under-designed real-scale beam specimens, strengthened with different FRP schemes.