This paper proposes a new modeling method for finite element analysis (FEA) to reproduce the delamination behavior of fiber-reinforced polymer (FRP) sheet bonded to the concrete. Three-point flexural tests of thin mortar specimens were conducted to clarify the characteristics of the mortar skin which represents concrete surface layer failed at the delamination. The thin mortar specimens that imitate the material composition of the mortar skin and the thin mortar specimens impregnated with primer were tested. In addition, the tensile strength and tensile fracture energy of each mortar skin were determined by inverse analysis using FEA in terms of the flexural stress-displacement relationship obtained from the tests. The flexural strength of the mortar skin in the concrete surface layer was higher than inner part of the concrete block. The strength was increased more when the primer was applied. Furthermore, the material constitutive law of mortar skin was introduced into the FEA. As a result, analytical results generally reproduced load-slip relationship, crack pattern, strain distribution, and bond stress-slip relationship.

In this study, a shear strength prediction AI model was developed for RC beams without shear reinforcements. The AI model is a neural network model which contains explanatory variables derived from mechanical interpretation such as the neutral axis and also variables on details of tensile reinforcing bars. The AI model can predict experimental results which contains wide range of shear span to effective depth ratio with high accuracy rather than a conventional neural network model and empirical shear strength equations. The AI model can apply to new data set without dependence on the train data. Furthermore, the AI model, in which Young’s modulus of the FRP reinforcements was taken into consideration in explanatory variables, can predict shear strengths of concrete beams reinforced with FRP reinforcements correctly.

In this study, single-lap shear tests were conducted using carbon fiber-reinforced polymer (CFRP) sheets. The parameters were the stiffness of the multi-ply CFRP sheets and bond length. Furthermore, the bond length and bond width were made larger than that in the previous experiments, in order to approach the actual reinforcement. Consequently, within the range of these tests, the debonding load increased as the number of CFRP sheet layers and stiffness increased. In addition, the three bond strength models showed good agreement. It was clarified that the actual effective bond length may be longer than the effective bond length measured from the strain gauges, owing to the influence of variations in the width direction.

In order to improve the bonding strength between FRP sheets and concrete, the FRP sheets bonding method using high elongation elastic resin as a buffer layer was developed. In this study, bonding tests was conducted using polyurea resin as the high elongation elastic resin and FRP strand sheets as the FRP sheets. As a result of the bonding test, it was found that the use of the polyurea resin as a buffer layer significantly improved the bonding strength and the interfacial fracture energy between FRP sheets and concrete with polyurea. In addition, bond stress-slip relationships with a polyurea resin were proposed. Finally numerical analyses of bonding CFRP sheets and concrete were conducted to verify validity of the proposed bond stress-slip relationships.

Aiming at improving bond strengths between FRP sheet and concrete, the FRP sheet bonding method using high elongation elastic resin as a buffer layer was developed. In this study, bonding tests was conducted to clarify the basic bond characteristics of FRP strand sheet-concrete interface with a polyurea resin. As a result of the bonding tests, it was found that the use of the polyurea resin as a buffer layer significantly improved the bond strength and the interfacial fracture energy between FRP sheets and concrete. In addition, bond stress-slip relationships with a polyurea resin were proposed. Finally, numerical analyses of bonding CFRP strand sheets and concrete were conducted so as to verify validity of the proposed bond stress-slip relationships. This paper is an extended version in English from the authors' previous work [Kobayashi, A., Ozaki, M., Sato, Y., Arazoe, M., Tateishi, A. and Komori, A., (2020). “Study on bonding behavior of FRP sheets and concrete bonded with high elongation elastic resin.” Journal of Structural Engineering, JSCE, 66A, 855-867. (in Japanese)].