Currently, the remaining riveted bridges are almost over 60 years old. Therefore, the rivets are corroded and loosen over time, deteriorated the condition of the bridges further. Previous studies have shown that replacing the riveted joints with a high-strength bolt for friction is considered the best approach to repairing the riveted joint in steel bridges. However, the current state is that the load transfer mechanism of the rivet and high-strength bolt friction joints is still unknown, and the load capacity of the combined joint has not been sufficiently discussed. Technical standards and design methods for repair have not been established. This study examined the load transfer mechanism and repair application range of the combined joint using the tensile test and FEM analysis.

This paper investigates the effect of beam section size and of beam-to-column connection type for mechanical behavior around the moment connection with FEM analysis. Firstly the bending moment of web connection was investigated by the global analysis. Secondly, factors affecting the initiation of ductile cracks was investigated by the local analysis using submodel. In conclusion, in the case of large section beams with bolted web type, the bending moment of web connection did not reach the estimated ultimate bending strength and the stress-strain concentration at the toe of the weld access hole was more noticeable.

An advanced mechanical properties estimation with instrumented indentation technique (IIT) using spherical indenter was applied to steels used in aged bridges. First, the effect of surface polishing on the variation in indentation load-depth curve was investigated to ensure the reliability of IIT. Under suitable testing condition, mechanical properties, such as stress-strain curve, yield stress and tensile strength, of aged steels was estimated and compared with tensile test results to validate the estimation accuracy. Meanwhile, the effect of heating and cooling process simulating fire was also evaluated by the IIT. It can be concluded from the results that the IIT is useful to estimate the mechanical properties of aged steels for bridges.

For investigating the applicability of shell elements for FE analysis of distortion and residual stress generated by fillet welding, a series of experiments and numerical analyses were carried out. Considering the temperature distribution in the thickness direction, the heat input model for fillet welding with changing the thickness of shell elements was proposed. The prediction accuracy of the welding out-of-plane deformation and residual stress by the model with shell elements was within 12% and 17% of those of the model with solid elements respectively. The computing time by the model with shell elements was around 4% to 13% of that by the model with solid elements.

In this study, we consider using large-diameter bolts for the standard thickness joints used in railway structures and making the minimum center spacing of the bolts smaller than the current standard. Then, we study for the purpose of shortening the length of the splicing plate and making it lighter. As a basic study, the relationship between the contact pressure and slip coefficient between the mother plate and the splicing plate when the tightening plate thickness was changed was confirmed analytically. In addition, we also verified the arrangement in which the minimum center interval of bolts is narrower than the current standard.

Due to the revision of the law, it became mandatory to conduct close visual inspection for all bridges every five years in 2014. Cables in cable-stayed bridges have been inspected visually using binoculars from the road surface, using aerial work platforms or using climbing techniques. However, these methods have problems such as safety concerns and long working time. To overcome these problems, the authors have developed a robot making it possible to approach and inspect cables safely and quickly. In this report, the feature of the cable inspection robot and examples of the inspect results using this robot are described.