Interfacial stresses in soffit-plated reinforced concrete beams

A popular new method for retrofitting reinforced concrete (RC) beams is to bond a fibre-reinforced polymer (FRP) plate to their soffit to increase their flexural strength. An important failure mode of such strengthened members is the debonding of the FRP plate from the concrete due to high interfacial stresses near the plate ends. This paper presents an explicit solution for interfacial stresses in a simply supported beam bonded with a thin plate and subjected to arbitrary loads. A set of arbitrary loads is decomposed into a symmetric component and an antisymmetric component. Closed-form solutions are derived for both the symmetric and antisymmetric load cases. The solution for arbitrary loading is obtained by superimposing the results for both load cases. The solution considers the non-uniform stress distributions in the adhesive, and satisfies the stress-free boundary condition at the ends of the adhesive layer and FRP.