This research has aimed to construct the fully automated high speed joining system with the end of the joining instantaneously, and enabling the application of the flash welding which does not require the skill to building structures. As for this joining method, the electric capacity for joining and weight of the device is too large to apply the flash welding to large section members and site joints. In order to decrease electric capacity, basic experiments were conducted with parameters of the current and the flash time. As a result, it was confirmed to be able to join steel materials of the circular cross section of 200cm² in the sectional area in electric capacity of 1/50 or less compared with the past. Moreover, it was confirmed that the joint of the H-shaped steels and the box section steels were also possible.

The cast iron deck is a lightweight deck slab with excellent fatigue resistance. There is a problem that the deck is separated when negative bending acts on the joint. As a countermeasure, we proposed a structure that uses both friction joint by the splice plate to the upper surface of the deck and tension type joint of end ribs. In this study, the relationship between friction and tension type joint and the slip strength were quantitatively clarified using FE analysis.

This research has aimed to construct the fully automated high speed joining system with the end of the joining instantaneously, and enabling the application of the flash welding which does not require the skill to building structures. As for this joining method, the electric capacity for joining and weight of the device is too large to apply the flash welding to large section members and site joints. In order to decrease electric capacity, basic experiments were conducted with parameters of the current and the flash time. As a result, it was confirmed to be able to join steel materials of the circular cross section of 200cm² in the sectional area in electric capacity of 1/50 or less compared with the past. Moreover, it was confirmed that the joint of the H-shaped steels and the box section steels were also possible.

Corrosion of hexagonal high-strength nuts used in infrastructures like steel bridges quickly occurs owing to the corner's thin coating, therefore becoming a burden on the maintenance system. This study conducts FEA to make the nut’s corner round and smooth, considering its stress distributions, then manufactures the novel shape nut. The mechanical performance of the set consisting of a hexagonal bolt and the novel nut was also investigated by tensile, tightening, and relaxation tests. Mechanical performances like tensile resistance, tightening property and the relaxation extent of bolt tensions between the novel and conventional shape nuts are almost identical.

In this study, it focused on the thin mortar layer applied to adjust the height of precast PC slab and steel girder. The effect of the thickness of thin mortar layer and the arrangement of headed stud on the shearing force of studs was examined by the push-out test. As the result, the stud shearing force lowered as the thickness of the thin mortar layer was thicker. In addition, the stud shearing force of the test specimen in which the headed studs were grouped arrangement was lower than the test specimen in which the headed studs were single arranged row. In addition, the examination was carried out for the proposal of the new design formula of the headed stud shearing force considering the thin mortar layer.

In this study, loaded fire resistance tests for a simple supported small-scale roof member specimen using a corrugated steel thin plate were conducted to clarify the basic fire resistance performance under transient state condition. The cross-sectional shape and distributed loads were used as the test parameters, and the collapse temperatures were examined. According to the test results, it was clarified that the corrugated steel plate specimens possessed the high load-bearing capacities at high temperature ≥650℃.

A drilling stop-hole is a tentative repair method for fatigue cracks. Some of the authors have proposed the method to reduce the stress concentration at stop-hole edge by bolting a crack. In the proposed method, reduction of crack opening displacement at bolted area contributed to reduction of stress concentration factor. In this study, to evaluate the fatigue strength reinforced by the proposed method, stress concentration factor at stop-hole is estimated based on the principle of superposition. Furthermore, a stress concentration factor at stop-hole reinforced by bolting a stop-hole and bolting a crack is evaluated. The validation of the estimated stress concentration factor at stop-hole reinforced by bolting a crack is confirmed by FE analysis.

Previous studies have been conducted on double frictional joints using high strength countersunk head bolts, including bolt head opening angles and torshear type high strength bolt. In order to further improve the pavement durability and field workability of steel deck plates, the use of high strength countersunk bolted single frictional joints with countersinking bolt hole in main plate is required. In this study, FE analysis simulating slip tests was conducted to evaluate the effects of bolt type, connecting plate thickness, and connecting plate configuration on the slip strength. The slip strength of the single frictional joint was primarily influenced by the bolt axial force reduction of the inner bolt. The high strength countersunk bolts exhibited a smaller yielding range of the hole wall during tightening and a lower axial force reduction rate compared to high strength bolts. As a result, the slip coefficient of the high strength countersunk bolts was higher than that of the high strength bolts.

This study purposed the validity of the total stress evaluation method by core sampling from steel bridges. Core-pulling experiments using a full-scale steel girder and a loading device was performed, and a measurement method to evaluate the stress from the strain generated around the circular hole using the basic theory of the drilling method was examined. The result was possible to calculate stresses close to those occurring in the member by using a measurement method that takes thermal effects into account. In addition, the problems of the measurement method were mentioned, and the possibility that the basic theory of the drilling method can be applied to the stress evaluation by core sampling was suggested.

Our research group has been developing 1,700 MPa class ultra-high-strength bolts and will try to rationalize bolted connections with the bolts. This study conducted mass production of 1,700 MPa class bolts and confirmed the tensile resistance experimentally. The slip behaviour of friction type bolted joints with them was also investigated. The mass-produced bolts demonstrated the stable tensile resistance derived from the used material. Slip test results of double-lap joints coated with inorganic zinc-rich paint found that the slip coefficient evaluated by the bolt tension before the test was larger than 0.45, and the bolt tension reduction through the slippage became less than about 3 percent.