Shear strengthening of beams with composite materials

This paper presents the results of an experimental/analytical study aiming at obtaining a clear understanding of the underlying mechanisms of the shear strengthening of reinforced concrete beams with fibre reinforced polymers (FRP). Through the definition of the generalised constitutive law of a bonded FRP sheet, of the compatibility imposed by the shear crack opening, and of the appropriate boundary conditions depending on the strengthening configuration, analytical expressions of the stress field in the FRP sheet crossing a shear crack are obtained. These expressions allow to easily define closed-form equations for the effective strength of FRP strips/sheets used for shear strengthening, as function of both the adopted strengthening configuration and some basic geometric and mechanical parameters. The FRP contribution is then added to those of concrete and steel. The equations 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.