On Analysis And Design Optimization Of Fatigue Of Steel Anchor Box Of The Cable-stayed Bridge Tower

The cable-stayed bridge is a kind of high order statically indeterminate system consists of stayed cable and supported by multiple points elasticity. The main girder is self-possessed and both the floor system and the traffic live load are transferred to the tower by the cable force follow the stayed cable.The cyclic repeated actions of the traffic live load make the stayed cable have the corresponding repeated alternating stress at the anchorage point of the ends of the main girder and the tower. The anchorages, which is at the ends of both girder and tower, are more and more widely adopts the form of steel anchor box. Under the actions of corresponding repeated alternating stress, the inner components in the steel anchor box starts to show up mutually connected micro cracks gradually. As time passed, these cracks may cause damages, this is the common basic principle of fatigue damage of steel.The steel anchor box, who’s the key part of the stayed cable bridge, works normally or not is related to the safety of the bridge. Hence, the fatigue of steel under the action of corresponding repeated alternating stress can not be ignored.In this paper, the project background is based on a stayed cable bridge who has spoke-type cable. The writer establishes finite element models of full-bridge and whole and local models of the global steel anchor box for the stayed cable at the tower. The paper analyzes the fatigue life and fatigue damage of the box under the action of automobile and earthquake based on the theory of nominal stress method of S-N curve and Miner linear cumulative damage. Following are the main job the writer has done for this paper.1. Use large finite element software to establish finite element models of the full-bridge, calculate and analyze the time-history curve of the cable force under the action of fatigue vehicle and earthquake.2. Use detail-analysis finite element software to establish whole and local models of the steel anchor box and to settle the key points of steel anchor box fatigue by static analysis. The time-history curve of the cable force from step 1 is substituted into the whole and local model, then get the stress time-history curve of every detail parts of the steel anchor box in the corresponding sate.3. Calculate the fatigue life and fatigue damage of the steel anchor box based on the theory of nominal stress method of S-N curve and Miner linear cumulative damage.4. Emphasizes on the analysis of different influences made by overloading and different peak values of earthquake at different rates to the fatigue strength of steel anchor box. Propose that the damage caused by seismic action equals to the traffic volumes of the standard fatigue vehicle, and suggest to apply this method to evaluate the influence of the earthquake on steel anchor box. This will be helpful for evaluating the fatigue strength of the indispensable steel anchor box during the bridge operation, and to provide reference for management and maintenance.5. Propose the optimization measures for steel anchor box designing according to the result of fatigue analysis and then evaluate the effect of the optimization project.