Intermediate debonding of FRP strengthened RC beams

In the present paper, first results of an experimental campaign concerning failure due to intermediate crack-induced (IC) debonding of r.c. beams strengthened with FRP composites (both CFRP plates and sheets) are presented. The simply-supported beam scheme with distributed load has been adopted in order to have a loading condition closest as possible to real cases. During tests, mid-span deflection, compressive strain, mean tensile elongation, crack opening and FRP strains along the beams have been measured. Effect of FRP reinforcement on flexural strength and ductility has been studied. Moreover, IC debonding type of failure has been identified from FRP strain distribution profiles. It is shown that IC debonding occurs where FRP strain is high but a gradient of it (associated with shear stresses along the interface according to classical beam theory) is also present. A characteristic behavior of FRP strain profile close to debonding has been also identified. Finally, comparison between experimental and theoretical prediction of FRP strains along the beam, close to failure, showed another way to localize intermediate crack debonding from FRP strain profile.