Stress Monitoring And Fatigue Damage Analysis Of Qiansimen Bridge During Operation Period

Urban rail transit develops rapidly,and the structural fatigue problem of dual-purpose steel bridges in urban public railways also increases with the increase in the number of new bridges.In view of the characteristics of urban rail transit vehicle loads,there is still a lack of clear description of the number of fatigue loads on the bridge caused by rail vehicles during fatigue analysis of dual-purpose steel bridges.Based on the stress monitoring test of the Qiansimen Bridge in Jialing River,this paper combines the theoretical analysis with the actual bridge stress monitoring analysis to study the stress of the Qiansimen Bridge and analyze its fatigue damage.This paper first introduces some basic concepts of fatigue analysis of steel bridges,fatigue analysis and calculation methods,and describes the use of fatigue damage accumulation theory.Secondly,based on the traffic data provided by the Chongqing Rail Transit Group,the light rail transit volume of the Qiansimen Bridge on the Jialing River was analyzed,and the fatigue spectrum of the light rail of the Qiansimen Bridge and the fatigue load spectrum of the light rail of the No.6 line were worked out.The fatigue load spectrum is converted to the equivalent equivalent fatigue standard axle load.The equivalent standard fatigue axle weight of the Qiansimen Bridge on the Chongqing light rail line No.6 is 94.33 kN,and the equivalent fatigue axis load of the entire rail transit line No.6 is 92.29 kN.Thirdly,in order to confirm the number of effective fatigue loads generated by the multiple loads generated by a single light rail line on the concerned position of the bridge structure,a stress monitoring test for the Qiansimen Bridge during the operational phase of the bridge was designed.The whole bridge model was established using Midas Civil finite element analysis software,and the equivalent standard fatigue axial weight was applied for static analysis to determine the weak fatigue section of the Qiansimen Bridge.Through the loading conditions of the whole model,it is judged that the upper vehicle load has less influence on the fatigue problem of the substructure,and the relative stress difference between the two on the substructure is nearly 90%.The ANSYS finite element software was used to perform local modeling analysis on the weak cross section position determined by the Qiansimen Gate Bridge using the standard cross section to simulate the stress history of each position of concern at the weak position of the light rail line No.6 line and to monitor the stress of the actual bridge.The data is compared and referenced.Finally,through actual measurement and theoretical data analysis,it is concluded that the beam at the position of interest of the lower structure is greatly affected by each axle load of the LRT train,and the stress amplitude generated by a single axle load is close to the stress generatedby the entire LRT train.The amplitude is half,so when considering the fatigue problem of the beam,it is necessary to consider the multiple axial loading of the light rail vehicle,while the lower longitudinal beam only needs to consider the effect of the overall load once the single train is loaded.The fatigue load spectrum obtained is loaded onto the integral finite element model to calculate the corresponding fatigue stress spectrum.Correct the fatigue stress spectrum,according to the fatigue details of the actual structure of the Qiansimen Bridge,select the corresponding S-N curve,and calculate the damage degree and residual fatigue life of the corresponding weak fatigue location of the bridge structure.Finally,it is concluded that there is no fatigue problem for the structure of the Millennium Bridge to meet the specification design requirements.