13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 4. Calculation example The stiffening girder of steel truss on one over-sea bridge is composed by main truss, main beam and upper and lower bracing. Main truss is connected by integral joint plate, and all the members’ sections are closed box. Main truss is composed by top chord members, lower chord members, vertical web members and inclined web members. Main truss is 10m tall, and each standard segment is 10m long. The structure of integral joint on top chord member is shown in figure1. It is made of Q345steel. This joint is under multi-direction stress, it has a complicated stress field. It is connected by large numbers of variable welding lines, so vehicle load could cause fatigue problem easily. 2--2 1 2 2 1--1 1 Fig.1 Schematic diagram of integral joint 4.1 Analysis based on crack mechanics Through finite element analysis, we know that there is obvious stress concentration at the intersection of integral joint plant and inclined web member. As shown in figure2, the biggest stress amplitude 84.4Mpa σΔ = .
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