What is made as materials researcher to use composite material (FRP) in the field of civil engineering works? When we have already experienced the phenomenon that we will meet with when we use FRP in civil engineering works for a long term by the chemical use. So, I want to assume it the help of the action by future civil engineering works by introducing a deterioration example of the FRP here.

 This paper deals with a repair method for the steel girder end with section loss by externally bonded CFRP strips. In case of applying structural adhesive with low elasticity and high viscosity, there are some problems of defects (internal void) and thickness in adhesive. In this study, the modeling of defects and interfacial stress in adhesive were analyzed using spring model, and the influence of defects and thickness in adhesive on the rehabilitation of steel girder end with section loss was investigated experimentally and analytically. The result shows that the influence of defects and thickness in adhesive on the recovery of compressive strength of steel girder end is relatively small.

 As a repair and strengthening method for steel structures, a method of bonding CFRP with resin has begun to be applied. Generally, in the CFRP bonding method, since the steel and the CFRP are designed on the premise of behaving as a complete composite in section, bonding lengths for transmitting loads to the CFRP are required on both sides. In some cases, the required bonding length becomes longer due to the rigidity of the CFRP layer, the thickness and the shear modulus of elasticity of the adhesive layer. In addition, corrosion of steel bridges often occurs in narrow parts and complicated shapes parts, and in some cases, it is difficult to secure required bonding lengths on both sides of the section to be reinforced.

 In this research, the authors focused on the case which the required bonding lengths cannot be obtained to be a complete composite in section, the tensile tests were conducted on the test specimens in which CFRP was adhered to a steel plate with insufficient bond length, and the influence on reinforcing effect was investigated. In addition, the experimental value compared with the theoretical value and proposed method of determining the reinforcement amount when the bond length is insufficient.

 In this study, a repair method of corroded steel girder end by using pultruded hybrid FRP angle sections is proposed. To examine performance recovery by using the proposed repair method, steel girder end specimens with thickness reduced portions were repaired by bonding hybrid FRP angle sections with and without FRP bolts, and compression tests were performed on these specimens. Results showed that the compressive bearing capacity of repaired specimens were recovered to the level equal to or more than that of the intact steel girder end specimen.

 Progressive damage analysis is one of the ways which can consider the nonlinear behavior of FRP composite materials. In the progressive damage analysis, the critical energy release rate is used to define the stress-strain relation after the initiation of damage. In this study, compact tension test (CT test) and compact compression test (CC test) were carried out to obtain the critical energy release rate of tensile and compressive failure modes in fiber direction of GFRP. To identify the crack length during the CT and CC tests, the digital image correlation method was used. From this study, it was shown that the critical energy release rate in tension is almost the same as the value obtained in the past research for a similar material, and that the critical energy release rate in tension exceeds the critical energy release rate in compression.

 FRP has been widely applied to repair and strengthening of concrete structures such as seismic strengthening of RC piers and fatigue strengthening of road bridge RC slabs since the 1990’s in Japan. “Recommendations for upgrading of concrete structures with use of continuous fiber sheets” had been published by concrete committee of Japan society of civil engineers in 2000. On the other hand, FRP has been beginning to be applied to repair and strengthening of steel structures in recent years. In addition, many researches on these applications have been being conducted in various research institutes. Therefore, subcommittee on guidelines for repair and strengthening of structures using FRP (H106) in hybrid structures committee of Japan society of civil engineers have carried out research studies on repair and strengthening of not only concrete structures but also steel structures. As a result, in order to propose design methods which can accurately predict mechanical performance and durability of structures repaired and strengthened using with FRP, and methods of construction and maintenance necessary for realizing these, “Guidelines for repair and strengthening of structures using externally bonded FRP” has been published.