Modeling of IC Debonding of FRP-Strengthened Concrete Flexural Members

Abstract

The presence of a fiber-reinforced polymer (FRP) strengthening material bonded to the tension face of a reinforced concrete beam will restrict but not prevent the opening of intermediate flexural cracks due to applied loading. Test results indicate that displacements at the toe of flexural cracks create stress concentrations at the interface of the FRP laminate and the beam, leading to the development of localized interface cracks that, typically, propagate, under the effect of the load, to join the original flexural cracks and cause delamination of the FRP system. This type of FRP delamination is commonly termed intermediate crack (IC) debonding. In this paper the analytical models published in the literature are reviewed and it was found that these models do not correlate well with measured experimental results. This paper proposes an analytical model that characterizes the interface shear stress based on two distinct sources: (1) the change in the applied moments along the length of the member and (2) stress concentrations at the intermediate cracks. The proposed model is compared to an experimental database and shown to predict extremely well most of the test results reported by other researchers. A parametric study, performed using the proposed model, indicates that the model varies with several important variables that are not captured by most of the existing models.