Study On Fatigue Performance Of Anchor Box Based On Equivalent Structural Stress Method

With the development of economy,society and transportation,higher requirements are put forward for the span ability of bridges,and the construction of steel structure bridges will increase in the future.Fatigue is a common phenomenon of steel bridge,which causes a series of accidents in operation.Therefore,fatigue problem has been concerned by scholars at home and abroad.Taking Dalian Coastal Avenue Westward Extension Line Cable-stayed Bridge as the engineering background,the anchor-box fatigue problem of pylon anchorage structure is studied in this paper.(1)The Midas full-scale model of Cable-stayed bridge is established.According to the anti-fatigue design stipulation of "JTG D64-2015 Specification for Design of Highway Steel Bridge",the number of the most disadvantageous cables is determined.Compared with the fatigue calculation results of American and British specifications,the maximum cable force amplitude is finally determined to be 430 kN.Considering the influence of average stress,Gerber theory is adopted to determine the loading value of full-scale model test.Sinusoidal wave is used for fatigue loading.The trough value is 50 kN,the peak value is 480 kN,and 2.26 million cycles of cyclic loading are required.(2)After 2 million cycles,through the analysis of stress and displacement data,the stress of the anchor box has not changed significantly and the stiffness has not deteriorated.No cracks have been found in the comprehensive magnetic particle testing results,which shows that the design can meet the requirements of the use.The structure has not been fatigue damaged after 2.76 million cycles,indicating that the anti-fatigue design of the anchor box has a large surplus.(3)Equivalent structural stress method is used to verify the insensitivity of the mesh.By comparing the mesh size of shell element and solid element,it is determined that 0.25 t plate thickness shell element is used for mesh generation,which can not only meet the requirements of the analysis,but also save computer operation time.Based on the symmetry of the anchor box,an half model of the anchor-box structure is established for analysis.The fatigue life evaluation results of the anchor box show that the overall life of the structure is more than 40 million times,which can meet the operation requirements of the bridge.(4)The thickness of the wall plate and shear plate of the pylon varies from 15 mm to 40 mm,and the fatigue life of the structure with different plate thickness is analyzed.The fatigue life curves of welding lines with different thickness are fitted,and the prediction results of the fitting curves are identical with simulation results.It is found that the fatigue life of the welded line on the shear plate is less affected by the thickness of the wall plate of the bridge pylon.With the increase of the thickness of the shear plate,the fatigue life increases correspondingly.When considering the safety factor,the thickness of 20 mm can be used to design the wall plate of the bridge pylon,while the fatigue life of the welded line on the wall plate of the bridge pylon is less affected by the shear plate,and increases with the increase of the thickness of the plate itself,the thickness plate of 25 mm can meet anti-fatigue design requirements.