Fatigue Life Assessment Of Integral Welded Joints Of Railway Steel Truss Bridge Based On Damage Mechanics

Integral welded joints have been widely used in steel truss bridges of highway and railway traffic trunk lines.However,due to many fatigue sensitive parts,complex internal structure and stress state,and the introduction of initial welding defects,the fatigue performance of integral welded joints is facing severe challenges.At the same time,with the development of transportation industry,the trend of “high speed and heavy load” further intensifies the structural dynamic response and fatigue damage effect of steel truss bridge,which brings adverse effects to the fatigue performance of integral welded joints.Accurately analyzing the fatigue damage evolution process of integral welded joints and carrying out fatigue life assessment are the basic premises for ensuring the safe service and driving safety of steel truss bridges.In this paper,a typical integral welded joints of railway steel truss bridge is taken as the research object,and the damage evolution process analysis and fatigue life evaluation of the integral welded joints of steel truss bridge are carried out by using the damage mechanics evaluation method.The main contents include:(1)The research status of commonly used fatigue resistance evaluation methods for steel structure bridges at home and abroad is reviewed.The necessity of using fatigue performance evaluation method based on damage mechanics to simulate the fatigue damage evolution process and predict the fatigue life of integral welded joints is clarified.The research objectives and research ideas of this paper are clarified.(2)Based on the fatigue test results of two types of welding structure detail models in the existing literature,the fatigue damage-related parameters obtained by fitting.The fatigue damage evolution analysis and fatigue life evaluation of unequal thickness butt weld specimens and cross joint specimens were carried out,and the results were compared with the test results,which verified the applicability of damage mechanics evaluation method in fatigue life prediction and fatigue damage evolution analysis.(3)Based on the whole bridge element model of a typical railway steel truss bridge,the location of fatigue vulnerable nodes is determined,and a uniform multi-scale finite element model is established,which contains local complex structural details and reflects the overall mechanical behavior of the structure.A simplified vehicle dynamics analysis model and a simplified vehicle-bridge system dynamics analysis model are established.The contact force method is used to complete the dynamic response analysis of the multi-scale finite element model of the steel truss bridge under single line loading.The multi-line coefficient of the fourline railway steel truss bridge is studied.(4)Based on the structural dynamic response obtained by single-line loading,the influence of multi-line train encounter on the dynamic response and fatigue damage effect of bridge structure is considered through multi-line coefficient.The life assessment and damage evolution analysis of two fatigue vulnerable joints were completed by using the material damage threshold index and the material damage accumulation index obtained by fitting the fatigue test results of the cross-joint specimen that can reflect the material information of the whole welding joint and the welding process.