The present study is intended as analysis investigations of fatigue durability of the trough to deck plate welded joint failed at weld root in deck plate. The investigations are carried out on the basis of three key factors: fatigue strengths of the welded details obtained by analysis method in conjunction with fatigue tests, stress ranges by FEM analyses with a unit wheel load, and the loads and their frequencies for the fatigue evaluations are the wheel loads in service, represented by an equivalent wheel load, assumed from the axle load measurements. Consistency between fatigue strength and stress range is simply demonstrated. Using this method for fatigue evaluation, it is found that large-rib-deck model has longer fatigue life than standard-deck models. An increase in deck plate thickness may prolong fatigue life of the orthotropic steel deck. Load distribution due to the rigidity of pavement may also help enhancement the fatigue life.

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This study performed an accelerated exposure test for 300 days to obtain the steel bridge repainting cycles quantitatively and examined corrosion characteristics of various repainted steel with differente surface preparations. Test specimens used in this study were cut out from the bridge girder used 36 years, and applied 3 types of surface preparation and 4 kinds of repainting systems. Each 3 specimens were taken out from the facility every 100 days, and evaluated the deterioration level by measuring brightness retention rate, blistering area and so on. By comparing the deterioration level of three types of surface preparation and 4 kinds of repainting systems, the repainting cycles of different paterns of spacimen were obtained.

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The purpose of this research is to investigate seismic performance for the large earthquakes and the effects of the concrete fill method as the retrofitting works of existing steel bridge frame piers with circular column. First, the design and the structural condition of their piers were surveyed. Next, pushover analyses and earthquake response analyses by using FEM were carried out on selected piers from the survey. As the results, although damage to some of their piers without retrofitting by concrete fill in the large earthquakes was serious, the damage was not significant with retrofitting by concrete fill. Moreover, it was found that the application of the method increased the response in the large earthquakes in case of the 2-story type of frame pier.

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Generally, the main water pipeline is built through installing steel pipes or iron pipes inside a shield tunnel or NATM tunnel and filling the annular void to form an integrated structure. However, the problem of buckling of inner pipe exists for such a structure because the most of the existing filling technologies fail to produce a tightly fitted liner. When the water pipeline is built deep underground, the separated structure should be adopted in order to ensure the minimum cross section of the tunnel as well as the safety of water pipe.
In this study, the buckling of stiffened water pipe used for separated structure is investigated. Firstly, the formulas of general buckling and local buckling are derived with Ritz method, and the methods of the formulas application are given in terms of the critical pressure calculation and the buckling behavior simulation. Secondly, the methods are verified by numerical analysis and existing experiments. Finally, the local buckling design method for separated water pipeline structure is proposed, taking into account of the buckling characters of a practical water pipeline.

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Fatigue strength and crack propagation behavior of cruciform welded joints in which fatigue cracks originate from weld roots have been already examined by a lot of studies under single axial loading condition. This study is aiming at constructing the evaluation formula for fatigue strength of cruciform welded joints failing from weld root under bi-axial loading. For the purpose, fatigue tests have been performed under bi-axial loading for 2 types of specimens with different weld penetration. Furthermore, fatigue crack propagation analyses have been also carried out with some variables, which are plate thickness, weld size, weld penetration and bi-axial loading ratio.

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This paper presents a spring-based cohesive crack model and its explicit solution method for the analysis of crack propagations in quasi-brittle materials. In the present method, the cohesive property between cracked surfaces is approximated as a kind of cohesive spring based on the penalty method instead of the traction force in conventional methods. We show the formulation of the spring-based cohesive crack model and detail the explicit solution algorithms for discrete crack propagation analyses in both the small strain and the finite strain problems. After demonstrating the capabilities of proposed method, we examine the mesh-size dependency in crack propagation analysis and study the performance of size effect of quasi-brittle structures in finite deformation problems. Finally, we demonstrate that the proposed method is stable and applicable even if a lot of cohesive cracks are included within the framework of multi-scale analysis based on the homogenization method under periodic boundary conditions which possibly causes the rigid-body motion.

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With recent advancement in the use of underground space, large underground structures, such as urban expressways, are being constructed. When a large underground structure spans from great depth to the surface, its high seismic resistance must be ensured by considering variation in the amplification of seismic motion with depth. The authors applied a large-scale three-dimensional dynamic finite element analysis to a ramp tunnel of a center-ramp type that is under construction on the Central Circular Shinjuku Route of Tokyo Metropolitan Expressway. An analytical model consisting of the ground and structures was developed, and the three-dimensional behavior of the model was computed for two input seismic waves. The analytical results were compared with those of a two-dimensional analysis, and the necessity and effectiveness of large-scale three-dimensional analyses for evaluating the three-dimensional seismic responses of large underground structures were discussed.

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