Research On Fatigue Properties Of Integral Joint Of Steel Truss Bridge Considering Welding Residual Stress

The integral joint of the steel truss bridge is complex,with numerous intersecting welds such as butt welds and fillet welds.There is great welding residual stress field in the integral joint.The integral gusset plate joint and the transversal beam joint of the integral joint directly bear the large vehicle load transmitted by the bridge deck.Therefore,the integral joint tends to crack easily.A fatigue properties evaluation method considering welding residual stress is needed to analyze the problem of great welding residual stress and fatigue cracking in the integral joint.This article takes a double-layer steel truss bridge with highway and railway as the research object.In order to solve the problem of fatigue cracking of the integral joint of the steel truss bridge,considering the influence of welding residual stress,basing on linear elastic fracture mechanics theory,the fatigue life and stress intensity factors of details is researched.The main research content and conclusion of this article are as follow:(1)A finite element model of the full-bridge of a double-layer steel truss bridge with highway and railway is established.Highway fatigue loading and railway loading is added on the most disadvantage lane and it is analyzed with load combination.The fatigue stress amplitude of chord members and web members are analyzed and the most disadvantage integral joint is obtained.The cruciform joint and the integral gusset plate joint are selected as fatigue detail of the integral joint.A full-bridge multiscale finite element model with the most disadvantage integral joint is established.The distribution of fatigue stress amplitude for two types of details are analyzed by adding highway fatigue loading and railway loading.(2)A thermal-mechanical finite element method is developed to predict the welding residual stress.The cruciform joint and the integral gusset plate joint are taken as the analysis object.The welding residual stress is analyzed by numerical simulation.The distribution of welding residual stress for two fatigue details is obtained.The release of welding residual stress under fatigue stress amplitude is considered.The change of the stress field of the cruciform joint after residual stress release is researched for further analysis.(3)Basing on the actual bridge welding process,the welding residual stress after post weld heat treatment of cruciform joint is analyzed.The effect of post weld heat treatment is researched.The results indicate that the welding residual stress will be released greatly after post weld heat treatment.The release of welding residual stress under the cyclic fatigue stress amplitude is considered.Finally,the welding residual stress field about fatigue analysis is obtained.(4)A fatigue life assessment method considering welding residual stress is established basing on linear elastic fracture mechanics theory.Under three loading cases that included post weld heat treatment and welding residual stress release,welding residual stress release directly without considering post weld heat treatment,and do not consider welding residual stress,the stress intensity factor and fatigue life of cruciform joint is analyzed.The stress intensity factor and fatigue life of the integral gusset plate joint is analyzed without considering welding residual stress.The results indicate that the fatigue life of cruciform joint has increased by 5.1%after using post weld heat treatment.The fatigue life without considering welding residual stress tends to be unsafe.Camparing with the fatigue life after using post weld heat treatment,the fatigue life is overvalued by 10.2%.Camparing with the fatigue life after releasing welding residual stress directly without considering post weld heat treatment,the fatigue life is overvalued by 15.8%.The cruciform joint tends to crack more easily than the integral gusset plate joint under the cyclic fatigue stress amplitude.The fatigue life of the most disadvantage integral joint is decided by the cruciform joint.