Fatigue Monitoring And Evaluation Of Hangers Of Steel-truss-arch Bridge Under High-speed Train

With the rapid development of high-speed railway,the safety performance of long-span railway bridges is attracting more and more attention.Under the action of moving train load,the bridge vibration response is remarkable.Hangers,as the main stress member of steel truss arch bridge,the fatigue performance of which will directly affect the service performance of the whole bridge structure.It is important to study the fatigue damage rule of full bridge suspender,especially the more stressed short suspender,for evaluating the health status of the whole structure.Taking Nanjing Dashengguan Yangtze River Bridge of Beijing-Shanghai high-speed railway as an engineering background,this paper focuses on the fatigue damage and life assessment of the hangers of the steel truss arch bridge based on the structural health monitoring data and the finite element simulation.The fatigue performance evaluation of the full bridge hanger is systematically studied.The main work is as follows:(1)The health monitoring system of Dashengguan Bridge is introduced.Based on the monitoring data,the train loads are divided into different working conditions according to the number of trains,the driving direction and the driving lane.The fatigue damage of suspender under different working conditions is analyzed,and the influencing factors are obtained.It is concluded that the fatigue damage caused by the bending-axial strain is larger than that of the axial strain.The closer the train track to the truss plane distance,the greater the fatigue damage caused by the train running on the truss plane.When the other conditions are the same,the fatigue damage of the hanger increases with the increasement of the carriage number of trains.There is no direct correlation between the fatigue damage of the hangers and the speed of the moving train.Based on the above conclusions,a fatigue failure probabilistic model for short suspender is established,and the MGD fitting method is applied to the number of cycles and the stress amplitude.(2)A full bridge finite element model is established to analyze the fatigue damage distribution rule of full bridge suspender.The results of finite element calculation show that the fatigue damage of the suspenders at the symmetrical position is different when the single train passes through.That is to say,the direction of the train will affect the fatigue damage of the hanger,and the position of the bridge transverse section and the number of trains on the train can have a significant influence on the fatigue property of the full bridge hanger.Based on the above results,the fatigue performance evaluation system of full bridge hangers is established.(3)A multi-scale fatigue analysis model of the short hanger nodal area of Dashengguan Bridge is built.Based on the multi axis fatigue theory,the fatigue damage of the short hanger of Dashengguan Bridge is studied and calculated.Based on the studies above,the change law of the multi axis fatigue damage of the short hanger node area is further discussed.The results show that the multiaxial fatigue life is only 1.69% of the uniaxial fatigue life,and the multiaxial fatigue damage to the node area is positively linearly related with the total vehicle flow,the proportion of 16-carriage-train in the total flow and the increasing ratio of the freight train.the greater the total traffic volume is,the greater the growth rate will be.Moreover,freight trains will greatly reduce the fatigue life of the nodal area.