S-N Curve Determination Of Structure Details In Steel Truss Suspension Bridge And Its Application In Fatigue Assessment

Suspension bridge has been widely applied in bridge engineering because of its super-long span.As the main structure form of double-deck suspension bridge,fully-weld steel truss structure has the advantages of light weight,convenient manufacture,high production efficiency,etc,but it also leads to the fatigue problem of welding parts.The welding hole intersection weld cause weakening of section,resulting in material of some parts of the structure brittle and fatigue strength greatly reduced.With the diversification of the bridge structure,many structural details can not been found in specifications.Therefore,the fatigue research of new key structure details in the welded steel truss beam cross welding hole has great theoretical significance and practical value of fatigue analysis.Wuhan Yang Si Gang Yangtze River bridge is a double-deck steel truss girder suspension bridge with the main span of 1700 m.As one of the important cross-river passage,the bridge has high load level and high fatigue risk level.As the first use of fully-welded steel truss girder in China,the weight of the beam is greatly reduced and a new type of structural detail has been produced.Based on the engineering application requirements,two kinds of structural details has been established by using the finite element software ANSYS Workbench to simulate the S-N curve of the cross hole structure of welded cross section.The three-dimensional finite element model of whole bridge is established by the software of MIDAS/civil to evaluate fatigue life.The following results have been achieved in this paper:(1)Two new steel truss beam cover plate butt weld and vertical plate butt weld cross welding hole structure details has been designed,one is arc transition and the other is right angle transition.Compare with the mechanical properties of the two structural details through the numerical simulation of ANSYS Workbench,the right angle transition is chosed for Yang Si Gang Yangtze River bridge.(2)Based on the nominal stress method,according to the fatigue performance of steel material used in main truss of Yang Si Gang Yangtze River bridge,the S-N curve of the structural detail is simulated by ANSYS Workbench.S-N curve expression of right angle transition structure detail is: N=+769.11lg005.3lg ?,the fatigue strength of the 2 million cycles is 66.47 MPa,S-N curve expression of reinforcement structure detail is: N=+44.12lg144.3lg ?,the fatigue strength of the 2 million cycles is 89.66 MPa.Results show that the fatigue strength has been improved significantly after reinforcement and the design requirements are satisfied.(3)The three-dimensional finite element model of whole bridge is established by the software of MIDAS/civil,the position of the element of maximum stress amplitude of the main truss is obtained based on the influence line,the loading vehicle from new specifications for design of highway steel bridge is used in the model,equivalent stress amplitude of 200 million cycles is got.Results show that the maximum stress amplitude of the main truss is 61 MPa,which is less than the allowable stress amplitude 89.66 MPa taken from reinforcing structure,so fatigue damage will not happen during the design life of 100 years in Yang Si Gang Yangtze River bridge.