Interface Stress Distribution in FRP-Strengthened Concrete Beams

In this study, an improved bi-material beam theory with adhesive interface is presented to evaluate the interface stress distributions of a concrete beam reinforced by an externally bonded fiber-reinforced plastic (FRP) composite plate. Both the adherend normal and tangential deformations induced by interface stresses are considered by introducing two interface compliances, from which an improved solution of interface stress distributions is obtained. Closed-form solutions of interface stresses are presented, and favorable agreements between the present solutions and those of the literature for a carbon FRP-strengthened concrete beam are achieved, thus demonstrating the validity of the solutions. The present improved bi-material beam theory provides a better prediction of the interface stress distributions, especially for adherend materials (i.e., beam and bonded plate) made of relatively low stiffness properties (e.g., wood material as the originally strengthened beam and thin FRP composite as the strengthening plate), and it can be used to analyze the interface debonding in the beams with externally adhesive-bonded plates.