Influence of hollow imperfections in adhesive on the interfacial bond behaviors of FRP-plated RC beams

Strengthening of reinforced concrete (RC) structures using fiber-reinforced polymer (FRP) composites has become a widely used structural strengthening technique due to the well-known advantages of FRP such as high strength, low weight, excellent resistance to corrosion and ease of installation. In this strengthening technique, the stress-transferring mechanism of FRP-to-concrete interface including adhesive layer is one of the key factors affecting strengthening effects and the failure modes of the strengthened members. Hollow imperfections usually exist in the adhesive layer due to many reasons such as air bubbles, concrete debris and unevenness of concrete surfaces, but the effects of such imperfections on the behaviors of FRP-plated beams are rarely investigated by existing studies. Against this background, this paper presents a finite element (FE) study on the effects of imperfections on the bond behaviors of the FRP-to-concrete bonded interface in an FRP-plated beam. In this study, an FE model with imperfections in adhesive layer was proposed in which the adhesive layer was modeled as an elastic material, and the interfacial bond behavior between concrete and adhesive was modeled based on Lu et al.'s bilinear bond-slip relationship. Based on the FE model, the influences of size and location of the imperfections on the interfacial bond behaviors (e.g. stress distributions) were investigated for non-prestressed FRP and prestressed FRP respectively. The numerical results show that for non-prestressed FRP, the existence of imperfections in the adhesive layer has a significant effect on the stress distributions in the vicinity of the imperfections. For prestressed FRP, the existence of imperfections leads to a significant increase of the shear stress in the concrete adjacent to the interface at the right boundary of the imperfection, as a result, the concrete next to the interface defect is prone to crack. The results also show that in the pre-stressed FRP case, the existence of imperfections leads to larger variations of the stress distributions in the adhesive layer at the boundaries of the imperfections compared with the non-prestressed FRP case. (C) 2011 Elsevier Ltd. All rights reserved.