Debonding strength of CFRP reinforced steel beams: analytical modelling and numerical analysis

Among the different techniques for retrofitting inadequate steel structures, the use of carbon fibre reinforced polymer (CFRP) materials was proposed due to their relevant properties for strengthening steel beams under static, fatigue or impact loading. In steel beams reinforced with CFRP materials bonded to the tension flange and subjected to flexural loading, collapse is mainly due to debonding of the CFRP strips or to the reinforcement failure. CFRP debonding is then the dominant failure mode and it prevents the achievement of the full flexural capacity of the composite section. In the literature, an outstanding attention was dedicated to precisely detect this failure mode. On the other hand, no general purpose formulation is available up to now. The aim of this work is then to provide a simple but reliable and safe predicting model for design purposes. For a linear cohesive law and an elastic behaviour of the steel beam, an analytical solution is achieved showing, for a general external loading configuration, the dependence of the debonding strength from both the fracture energy and the maximum shear stress at the interface. Experimental data from the literature are used to validate the proposed analytical model while a parametric analysis are performed to clarify the proposed formulation. To this end, a numerical method based on the cohesive law recently proposed in the literature is used to corroborate the analytical results