| Welded steel structure has been widely used in the bridge engineering,but the welded joints easily lead to fatigue problems due to welding residual stress generated inevitably in the welding process.With the current code and fatigue-life evaluation methods,it is difficult to consider the real value of welding residual stress.To ensure the accuracy of fatigue life assessment,based on the Goodman formula and the relevant empirical theory,a new method is proposed to determine the structural fatigue performance by correcting the S-N curve of the material using the welding residual stress,which can be calculated by the thermal-structural coupling welding residual stress numerical simulation method.And the feasibility of the method is verified.In order to further improve the reliability of the structure,considering the initial crack caused by welding damage,the fatigue crack propagation behavior is analyzed based on the fracture mechanics theory.The S-N curve of structural detail is obtained,and the discrete interval of structural fatigue strength is predicted to ensure the safety of the structure.The Wuhan Yang Si Gang Yangtze River Bridge is a double-deck steel truss girder suspension bridge with a large span.The load level and fatigue risk level are very high,and it's the first use of fully-welded steel truss girder in China.Based on the engineering application requirements,the fatigue performance of the welded detail with cope hole is analyzed by using the theoretical method to determine the fatigue behavior of the steel truss girder.The equivalent stress amplitude of the most unfavorable bar is calculated,so the fatigue life of the main truss bar is evaluated.The following results have been achieved in this paper:(1)The finite element calculation is carried out by using the hot stress method to analyze the stress concentration at the arc of the welding hole.By means of parameter analysis,the radius of the circular arc and the right angle transition form and the arc one are compared,which indicates that the radius of the arc should not be made too large,and the right angle transition form is better than the arc one in mechanical performance.(2)The finite element thermo-structural coupling analysis method is used to simulate the welding residual stress of the welded detail with cope hole.The results show that there is a large residual stress at the weld toe position.The maximum equivalent welding residual stress is 266 MPa,reaching 77.1% of the material yield strength.It should be fully considered in the fatigue assessment.(3)According to the proposed S-N curve calculation model,considering the welding residual stress and other factors to modify the S-N curve of the material,the S-N curve of the welded detail with cope hole is obtained.And based on the fracture mechanics theory,taking into account the initial crack,the S-N curve of the welded detail with cope hole is obtained,so that the fatigue strength interval of 2 million times is 51.88 MPa ~ 57.41 MPa.(4)The three-dimensional finite element model of whole bridge of the Wuhan Yang Si Gang Yangtze River Bridge is established,the position of the most unfavorable bar position of steel truss girder is obtained by adopting the standard fatigue truck of 445 KN in China and the loading mode of multi-lane in British standard BS5400.Based on the flow rate prediction and fatigue damage equivalent theory,the equivalent stress amplitude of the most dangerous part of the steel truss is obtained.The results show that the maximum equivalent stress amplitude is 39.03 MPa,which is lower than the fatigue strength at 2 million cycles for the structure detail corresponding to the theoretical structural S-N curve based on the proposed method.So the fatigue life of the main truss bar of the Wuhan Yang Si Gang Yangtze River Bridge meets the design requirements. |
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