Prestressed concrete (PC) is a structural method that can effectively reinforce concrete, which has a weak tensile property. However, in recent years, deterioration phenomena have been confirmed in which rein-forcing bars and prestressing steel members placed inside the structure corrode. Because this deterioration phenomenon progresses inside the concrete, it is difficult to detect early. Therefore, various measures to improve the durability of PC structures have been developed. One of these methods is the non-metallic bridge that is a composite structure that uses aramid FRP rods, which are made by molding aramid fibers into a rod shape with resin, as tension members and completely eliminates the use of reinforcing bars and ordinary prestressing steel members, which are likely to corrode. In this paper, an overview of various experiments conducted to realize this structure are provided and introduced examples of applying this structure to an actual structure. Furthermore, the outlook for expanding the application of such new structures is presented.

 Steel tube bases used for signposts are prone to accelerate the corrosion near the boundary with ground due to crevice corrosion. Carbon fiber reinforced plastic (CFRP) is used to repair such corrosion in steel tube structures. For CFRP bonded repairs and strengthening, it is critical to ensure proper bond length and prevent delamination of CFRP to achieve effective repair and reinforcement. In this study, shear-lag theory is applied to CFRP-bonded cantilever steel tubes to derive the shared bending moments in the steel tube and the CFRP, as well as the shear stress in the adhesive. The derived equations were validated by comparison with finite element (FE) analysis. In addition, the study proposes a required bond length for CFRP bonded repairs and strengthening, which was confirmed by FE analysis of ribbed steel tubes.

 FRP hydraulic gates are designed and verified based on allowable stress and deflection limitation in accordance with design standards, however, the limit states of safety and serviceability of the actual structures have not been sufficiently discussed. In this study, for the purpose of understanding the structural characteristics of small FRP hydraulic gates and developing a rational design method, two types of small FRP hydraulic gates and a small steel hydraulic gates based on the current design were experimentally tested for water pressure up to failure to understand the limit state, and a rational cross-sectional design for the design water pressure was studied by FEM analysis. The results showed that the designed FRP hydraulic gates could be rationalized because it is sufficiently safe and has sufficient margin, although the deflection limitation is dominant in the design, and that the minimum member height that satisfies the deflection limitation can be drastically reduced.

 Buckling-restrained braces (BRBs), which are widely used as seismic countermeasures for bracing members, are fabricated with steel and/or mortar, however, the overall weight of the member is large, so it makes the construction easier and the range of application wider if the weight can be reduced. The objective in this study is to develop lightweight CFRP BRBs. Test specimens of the CFRP ribbed BRB and the CFRP box-shaped BRB with stiffness equivalent to that of the conventional steel ribbed BRB were fabricated, and cyclic loading tests were conducted on the steel ribbed BRB and two types of prototype CFRP BRBs to investigate the validity of the proposed BRBs. As a result, it was confirmed that the CFRP box-shaped BRB has a reasonable cross-sectional shape, since it has equivalent performance to the steel-ribbed BRB at about 1/6 of its weight.

 It has been confirmed that bonding steel plates to GFRP plates for reinforcement improves joint strength and enables the application of high-strength bolted frictional joints. However, due to the creep characteristics of GFRP, the axial force of bolts decreases over time, which becomes particularly pronounced at high temperatures. Therefore, in this study, as a countermeasure against the creep of GFRP plates, we attempted to suppress the decrease in bolt axial force by enlarging the bolt holes in the GFRP plates to the diameter of the washers and inserting circular steel plates with the same diameter as the bolt holes. The temporal changes in bolt axial force were examined through temperature variation tests using a low-temperature constant temperature and humidity chamber, and the joint strength was evaluated through tensile tests of the high-strength bolted frictional joints. The results confirmed that while maintaining sufficient joint strength, it is possible to suppress the decrease in axial force at high temperatures. On the other hand, it was found that the decrease in axial force at low temperatures is greater compared to the conventional joint method.

 Permanent scaffolds made of GFRP are increasingly being installed to improve the efficiency of inspection and repair of bridges and overpasses. Permanent scaffolds are expected to be used as scaffolds for repainting, and it is necessary to understand their performance as scaffolds when the coating film or solvent burns off during the work.

 In this study, the degree of decrease in material properties as a function of combustion temperature and time was confirmed by combustion tests using specimens, and the material properties after heating were examined by conducting heating tests assuming a fire. As a result, there was no change in the material properties of GFRP at 340°C. At 680°C, the surface on the flame side burned, but all of the 5-mm-thick plate did not burn after about 30 minutes of combustion, and it was confirmed that the material could hold a load that a worker could place on it when a loading test was conducted after combustion.

 To enable daytime traffic opening during deck replacement in large-scale reconstruction projects, a GFRP (Glass Fiber Reinforced Polymer) paving cover plate was developed to temporarily bypass the need for filling concrete and asphalt paving. This study evaluated its practicality through a series of tests. Static load tests confirmed sufficient load capacity and no deformation at attachment bolts. Vehicle and wheel load tests showed no issues with the cover plate or bolts. However, the wheel load tests indicated that GFRP corner pipes should be placed densely to prevent fatigue failure and ensure durability.

 Seismic retrofitting of steel bridges typically involves the use of steel plates to strengthen the structure. This method has problems such as loss of cross-section of the base material due to bolt holes, increase in dead weight, and re-deterioration. To solve these problems, it is effective to use carbon fiber reinforced polymer (CFRP) for reinforcement, which is lightweight and does not corrode. In this study, we conducted monotonic and cyclic loading tests on long rectangular section specimens made of steel truss bridge members and verified the seismic reinforcing effect of CFRP sheets. As a result, it was confirmed that CFRP reinforcement can be expected to improve the load-carrying capacity even under cyclic loading, and that the amount of energy absorbed does not suddenly decrease even after local buckling occurs. In addition, the experimental results were on the safe side of the load-carrying curve, and it was found that it was possible to incorporate the reinforcing effect of CFRP into the design by using the existing load-carrying curve.

 FRP sheets are widely used to strengthen the seismic resistance of bridge piers but are also known to be susceptible to ultraviolet light in some cases. We conducted exposure tests and static loading tests to investigate FRP’s degradation process.

 This report presents how the carbon and aramid fibers changed during the five years of exposure and proposes measures when FRP sheets applied to bridge piers are exposed to ultraviolet light.

 GFRP (Glass Fiber Reinforced Polymers) possesses excellent strength-to-weight ratio and durability. However, there are still many uncertainties surrounding the evaluation of damage in GFRP. Particularly, small cracks in the resin and delamination due to fatigue damage are challenging to detect visually. Therefore, this study focuses on investigating a fatigue damage evaluation method using capacitance. Initially, authors conducted a tensile fatigue test on a specimen with electrodes bonded to both sides of the GFRP. This test revealed that the occurrence of cracks in the resin, which is an early sign of fatigue damage, does not affect the capacitance. Following this, authors created a GFRP with electrodes embedded inside and conducted tensile fatigue tests to investigate the relationship between capacitance, the number of cycles, and residual stiffness. The experiment demonstrated that the capacitance decreased as delamination progressed from the middle of the fatigue life onwards. This finding indicates that it is possible to evaluate fatigue damage based on the decrease in capacitance. However, the experiment also highlighted the importance of ensuring the durability of the electrodes themselves.

 Adding stiffening steel plates with high strength bolts is generally used to reinforce the load-bearing capacity of steel truss bridges. However, this method causes the cross-section of the steel member to be reduced due to the bolt holes, which increases the amount of reinforcement required. A reinforcement method using carbon fiber reinforced polymer (CFRP), which is stronger, more elastic, lighter, and less corrosive than steel, has been proposed as a potential solution to these problems. If a reinforcement method using CFRP could be applied, it would be a more rational method than reinforcement using steel plates.

 In this study, mainly for seismic reinforcement, CFRP sheets were attached to long column specimens that imitated the H-section diagonal members of steel truss bridges to examine the reinforcement effect through cyclic behavior under compression and tension loading tests.

 During fatigue damage to the steel deck, fatigue cracks propagate starting from the U-rib welds. As a countermeasure against such fatigue damage, SFRC pavement construction is a standard construction method. However, lane regulation is required and causes traffic congestion. Therefore, we are considering a reinforcement method using lightweight resin mortar filled in the U-ribs and CFRP molded material pasted between the U-ribs as a reinforcement method from the bottom of the steel deck slab. In this study, we performed a steel deck specimen with three U-ribs, filled the U-ribs with lightweight resin mortar, secondary injection of resin, and pasted CFRP molding material between the U-ribs. The reinforcement effect and durability were confirmed through the moving wheel trucking test.

 CFRP, which is lightweight, high-strength, and highly durable, is rapidly being applied in automobiles, aerospace, and sports equipment fields. However, developing effective recycling methods is necessary since the waste is treated as industrial waste after use. Recently, recycling technologies for recovering CFRP from waste materials have been advancing, but there is still a lack of practical applications for effectively using the recovered recycled carbon fiber. This study focuses on the potential of recycled carbon fibers to enhance the performance of FRP in orthogonal and shear directions, which are weak points caused by the anisotropic nature of FRP. First, the physical properties of matrix resin mixed with recycled carbon fibers are evaluated. Next, the effects of milled recycled carbon fibers on the mechanical properties of the FRP matrix resin are analyzed, and nondestructive internal observations of these properties are conducted.

 FRP materials that have superior material properties, e.g., high elastic modulus, high weight-strength ratio and corrosion resistance, have been widely applied to industrial, aerospace, and construction use in recent. In the construction field, the repair and strengthening method using FRPs has been strongly researched and developed. Almost methods adopt the adhesive bonding method to apply FRPs to the existing structure surface. This paper shows a new strengthening method and mechanism using thin FRP restrainers. Because of the high elastic deformation performance of FRP, the plastic band-like application method can be used for the setup. Therefore, the authors proposed an unbonded reinforcement method that does not require consideration of delamination. In this study, we report the results of basic experimental investigations on the forming method, construction method, and design method of a method to improve the stiffness of GFRP pipes cut in the center by using slit pipe shaped unbonded FRP.

 This subcommittee investigated a future management system of infrastructures for realizing “Society 5.0” presented by Cabinet Office, Government of Japan in the 5th and 6th Basic Plans on Science, Technology and Innovation. The current report discusses expected social infrastructures according to the vision of Society 5.0, and summarizes the future ideal systems in design, construction and maintenance of infrastructures based on the necessary technologies for realization of Society 5.0. Then the current state of Digital-Twin technology, a key issue for the future ideal systems, is reported through the investigations on the several on-going projects. Technical issues to realize Digital-Twin of infrastructures are finally summarized into three categories, Building of cyber space, Information acquisition in physical space, and Feedback from cyber space to physical one.