Debonding failures in RC beams and slabs strengthened with FRP plates

Abstract

Strengthening of reinforced concrete (RC) structures by the external bonding of advanced fibre-reinforced polymer (FRP) composites has become very popular around the world over the past decade due to the well-known advantages of FRP composites over other materials including their high strength-to-weight ratio and good corrosion resistance. Such FRP-strengthened structures are likely to fail by debonding of the FRP from the concrete. As a result, debonding failures in FRP-strengthened RC structures have received a great deal of research attention. Due to the complexity of debonding failures, considerable uncertainty still exists with the failure mechanisms and the prediction of debonding failure loads. This thesis presents an in-depth study aimed at the development of a better understanding of debonding failures in RC beams/slabs strengthened by bonding an FRP plate to the tension face of the concrete member (i.e. FRP-plated RC beams/slabs), and at the establishment of more reliable predictive models. Following an introduction to the subject and a review of existing research, the thesis presents an extensive experimental investigation into the bond behaviour between externally bonded FRP and concrete. A simple test apparatus was designed and fabricated and 72 pull tests were conducted on simple FRP-to-concrete bonded joints using this apparatus. These tests covered a number of significant parameters over a wide range and delivered results which are in close agreement with the predictions of Chen and Teng's (2001) model, which thus confirms the reliability of both the test method and Chen and Teng's model. Furthermore, by making use of the extensive strain measurements in some of the pull tests and a recent analytical solution for bond behaviour, the interfacial parameters of these specimens were identified to establish bond-slip curves. A comparison of the pull tests and the analytical solution for the full-range behaviour of bonded joints confirms the feasibility of this approach of identifying interfacial parameters and provides further insight into the debonding failure process of these bonded joints. Debonding failures in FRP-plated RC beams and slabs may be induced by intermediate flexural or flexural-shear cracks (i.e. IC debonding). The results of 22 tests on FRP-plated RC slabs are presented. Through these test results, the failure process and the failure mechanism are careflully examined. The present results together with results from existing studies are then used to assess the accuracy of existing IC debonding strength models. Debonding is also likely to occur at a plate end (i.e. plate end debonding). The results of 21 tests on plate end debonding are presented in the thesis. These tests cover a variety of significant geometric and material parameters over a wide range and led to an improved understanding of the failure processes. These test results together with existing test results are used to develop a new, more accurate plate end debonding strength model, as the existing models are found to be inadequate. The new model takes into account the shear-bending interaction at the plate end.