The authors previously proposed a method for the detection of fatigue cracks based on changes in the strain under an unloading condition near the weld toe. This method utilizes the strain change that occurs due to the release of residual stress introduced by the welding. However, the strain change near the weld toe becomes small once the fatigue crack has propagated. Therefore, this study focused on the area around the fatigue crack tip, where the authors found that fatigue crack propagation can be detected by monitoring changes in strain under the unloading condition.

Stiffened rectangular steel piers, often used for bridges, provide high stiffness and buckling resistance. However, the seismic impact of initial imperfections remains unclear, as they can trigger buckling under cyclic horizontal loading, potentially reducing load capacity. This study utilized 3D finite element analysis on SBHS500 steel piers to assess this specific impact. Comparing models with and without these imperfections, the analysis indicated that the mechanical behavior was not clearly affected by the initial imperfection conditions considered in this investigation.

The frequency of bridge damage, such as from accidental fires during repainting and fires from tank lorry vehicle overturning accidents, has increased in Japan and in other countries. Therefore, it is necessary to make clear the influence of the strength reduction after fire. The purpose of this study is to evaluate the fatigue behavior of composite girder after fire. We carried out the fatigue test of composite girder after fire test. As a result, it was confirmed that the headed studs between steel girder and composite slab were broken at the cyclic number 780,000 when they were subjected to thermal history of 680℃ for 30 minutes.

This study analyzed adherent rust remaining on steel members using Raman spectroscopy and identified magnetite as the primary component, with localized β-FeOOH near the steel surface. When a CS coating was applied over the rust, it demonstrated corrosion resistance comparable to hot-dip galvanizing for up to 160 cycles, and the zinc in the coating was expected to provide electrochemical protection to the steel substrate through anodic reaction.

To enhance the seismic safety of bridge structures, steel bellows-type dampers were developed by the authors and their effectiveness confirmed through experiments and FEM analysis. This study analytically investigates bridge seismic performance equipped with both bellows-type dampers and bearing displacement restraints that allow plastic deformation. Non-linear time-history analyses show that the system prevents force concentration on bearings, controls superstructure displacement within joint gaps to reduce collision risk. The results also show that this combined system effectively reduces large upward forces under Level 2 earthquakes, demonstrating the validity of the proposed design method.

In recent years, bridges have been deteriorating, and more efficient repair methods are required. One of the repair methods often used when steel bridges become corroded is the use of patch plates. In this study, patch plate repair using high strength bolt friction joints is focused on. Previous studies on patch repair have examined cases where the shape of the thinned area is uniform. However, no study has been conducted on cases where the shape of the thinned portion is not uniform. Therefore, in this study, an analysis was conducted assuming a case in which the shape of the thinned area is not uniform. The effect of the shape of the thinned area on the load distribution of the patch plate repair was examined.