Intermediate debonding on cracked steel beams reinforced with CFRP plates under fatigue

Externally bonding by using Carbon Fibre Reinforced Polymers (CFRP) plates is often regarded as an effective technique to strengthen notched steel beams. On the other hand, intermediate debonding in the reinforced steel beam has a significant effect on fatigue crack propagation. Note that the fatigue load does not directly cause the debonding, but it may trigger crack propagation in the steel substrate, leading to the propagation of the debonded region. At first, the outcomes from an experimental campaign previously conducted at the Politecnico di Milano were considered. Then, analytical and numerical models were proposed to evaluate the strain distribution in the reinforcement at a given crack length. A good agreement was found among the analytical, numerical and experimental results in terms of strain distribution in the CFRP material.