Influence Of Marshalling Changes On Fatigue Load Amplitude And Lifetime Of Light Rail Supports

With the rapid development of social economy,urban rail transit has gradually become the dominant mode of transportation in cities.Because of its characteristics of large capacity,high speed,safety,reliability and comfort,Chongqing Light Rail Transit has become the first choice for residents to travel.As an important component of rail transit,the light rail support plays a crucial role in the safe operation of the light rail.According to the survey,most of the damage to the structure is due to fatigue failure of structural details.The actual operation mode of different marshalled trains on the Chongqing Light Rail Line 3 is very different from the originally designed operation plan,which will have a significant impact on the fatigue performance of the light rail support.In order to further ensure the normal operation of the light rail during the reference life period,this paper uses the light rail line 3 of Chongqing Caiyuanba Yangtze River Bridge as the engineering background to study the fatigue performance of the light rail support before and after the light rail train marshalling changes.This paper first investigates the traffic volume of the light rail line 3 of Chongqing Caiyuanba Yangtze River Bridge to determine the number of fatigue loads and interactions of the track beam.Afterwards,using the influence lines of the track beam to extract the respective reaction force course of the light rail bearings under the operation of the four formation,six formation and eight formation trains.Utilizing the Linear Fatigue Damage Theory to calculate the Equivalent Load Amplitude of the four formation,sixth and eighth formation trains.Next,through the processing methods for the low stress cycles in the European Eurocode3 and British BS5400 specifications,the equivalent load amplitude of the light rail train is converted from a low value high frequency to a high value low frequency test load amplitude.The finite element software ANSYS15.0 was used to model the light rail support of Chongqing Caiyuanba Yangtze River Bridge,and the amplitude of the test load before and after the change of the light rail train marshaling is applied to the support model,and the distribution results of the first principal stress and Mises equivalent stress under different conditions are obtained.Based on the static analysis results of the finite element model of the Caiyuanba Changjiang River Bridge light rail support in Chongqing,the provisions of the "Code for Design of Highway Steel Bridges"(JTG D64-2015),British BS5400,US AASHTO and European Eurocode are applied to check fatigue.The fatigue strength of Chongqing Caiyuanba Yangtze River Bridge light rail support was checked and calculated.Then,the node position of the maximum stress of the light rail support model before and after the change of the light rail train marshalling is selected.The Fatigue module in the ANSYS postprocessor is used to calculate the fatigue life and fatigue damage coefficient of the light rail support node.After obtaining the results that the fatigue life is far greater than the number of design stress cycles and the fatigue damage factor is much less than 1,It can be judged that the fatigue performance of Chongqing Caiyuanba Yangtze River Bridge light rail support is sufficient to meet its design requirements.In other words,the light rail support will not have fatigue damage during the design reference period,and the operational safety of the light rail will be further protected.