Bond behaviour of fibre reinforced polymer strengthened concrete structures using advanced composite processing techniques

摘要

The research presented in this thesis consists of experimental, analytical and numerical studies of the interface behaviour in adhesively bonded joints manufactured with common and new developed FRP processing methods. The wet lay-up and pultruded laminates are categorized as common, and vacuum assisted resin infusion (VARI) and heated vacuum bag only (HVBO) are considered as recently developed processing methods. The effect of the principal parameters on the interface behaviour is studied through several series of experiments. Local and global investigations of the interface indicate that through application of VARI and HVBO, a bond with high quality is achievable. To monitor the bond characteristics during the experiments, a new single lap shear test set-up is developed and employed in this research. Results indicate that accurate and reliable results can be achieved in terms of interfacial responses using modified single lap shear test set-up. Through the experimental program, the effect of the bondline thickness is specifically studied for different types of processing techniques. Investigation on the local and global bond parameters show that after a specific bondline thickness, load carrying capacity of the joint does not change. Therefore, a new concept, the optimum bondline thickness, is proposed and the load-bondline thickness relationships are adopted based on the nonlinear regression analysis of the experimental results. Since in this research various techniques are compared and considering this fact that the fabrication method in these techniques is different therefore, the bond characteristics are scaled in a way that the comparison can be possible. This scaling factor here is called “equalisation of the processing techniques.” A new analytical approach is presented for determination of the interface behaviour in FRP-to-concrete bonded joints. Based on the boundary conditions, two distinctive methods are proposed to predict the bond-slip relationships and interfacial fracture energy. Since the models are derived solely based on boundary conditions of the joints, they can be applied to any type of the FRP processing technique. In addition, the interface characteristics are obtained from the value of the applied load at each stage and the properties of the materials which are available in most of the tests. Comparison between the experimental and the analytical results of the maximum load carrying capacity, the strain, shear stress and slip profiles and also the fracture energy of the interface indicate that the proposed analytical methods are capable to predict the interfacial behaviour between the FRP and concrete substrates with satisfactory precision. Finally, considering the proper material constitutive laws, a finite element analysis is carried out and the outcomes are presented.