Orthotropic steel bridge decks (OSDs) are widely used in the long-span bridges, movable bridges and urban viaducts. However, many fatigue cracks in orthotropic steel bridge decks were reported in japan recently. Among these fatigue cracks, the cracks occurred around the rib to deck joints are most critical, because the rib-to-deck (RD) joint fatigue cracks will cause the asphalt surfacing damage steel corrosion. The purpose of this study is investigating the asphalt surfacing influence on the

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... tigue life of the RD joint and fatigue strength of RD joint with various welding details. In chapter 1, the background of the cause of fatigue damage and fatigue crack initiation and propagation mechanics of metals and welding joints are introduced. Various fatigue life evaluation methods are discussed. Among these fatigue evaluation methods the fatigue strength classification for various welding joints and loading conditions based on the S-N curves are most widely used in fatigue design specifications or recommendations. Moreover, for the fatigue cracks initiation from the weld toe and the welding joint is not covered by the fatigue strength classification, the structure hotspot stress method is recommended by the JSSC and IIW to be employed to evaluate the fatigue life i.e. using the hotspot stress instead of normal stress based on the fatigue strength classification of the corresponding cruciform welding joint. The linear elastic fracture mechanics (LEFM) is generally used to evaluate the fatigue life of the welding joint which is not covered by the fatigue strength classification welding joint details and the fatigue crack initiating from the weld root. In the chapter 2, the historical development of OSDs is reviewed. Some strengthen and refit methods for the RD joint are also introduced in this chapter. The macro analysis of rib-to-deck fatigue cracks in the Wangan route of Hanshin expressway was carried out in this chapter. The macro analysis result shows that most fatigue cracks around the RD joint located in the driving lines with large traffic volume of heavy load axles. And all the RD fatigue cracks are located in the transverse range of 800mm from tire center. It could be concluded that the fatigue damage of rib-to-deck joint is significantly sensitive to the volume of heavy load axles and transverse locations of wheel loads. So in chapter 3, for the purpose to investigate the relationship of the stress around RD joints and wheel load location, a Finite Element (FE) model of partial orthotropic steel deck was made using the general purpose FE software Abaqus. The calculation result shows that stresses around the RD joint are significantly sensitive to the transverse loading location. With respect to the cross section Professor of Structure Engineering, in the Department of Civil and Earth Resources Engineering, Kyoto University, for his precious guidance, encouragement and support throughout this study.