Study On Fatigue Design Load Standard Of Rail Transit Bridge Structure

With the continuous development of urban construction in China,rail transit construction is in the ascendant.For mountain cities such as Chongqing,more and more large-span rail transit bridges are built,and steel structure bridges are mainly used.According to the current bridge design code,there are still some deficiencies in the fatigue design of rail transit bridge steel structure.Based on the Chongqing Science and Technology Project "Research on Transverse Stiffness and Fatigue Design of Steel Box Girder of Long Span Urban Rail Transit Bridge",this paper mainly studies the load standards needed in fatigue design of rail transit bridge:(1)Focusing on the development of rail transit and rail transit steel bridges and fatigue problems of steel bridges,this paper summarizes the research status of fatigue design loads of highways and railways at home and abroad,which provides reference for the research and formulation of fatigue design loads of rail transit.In order to determine the mode of fatigue design load,the operation status of Chongqing rail transit lines and vehicles was investigated,and the design load multiplied by the reduction factor was used as the fatigue design load.Based on Chongqing Rail Transit Passenger Flow Data Analysis Service Platform,passenger flow and vehicle data are introduced,which lays a foundation for formulating rail transit fatigue design load.(2)Based on the analysis of cross-section passenger flow characteristics of Chongqing Rail Transit Line 1,Line 2,Line 3,Line 6 and Shanghai Rail Transit Line 1 and Line 10 in different periods,this paper puts forward the statistical method of crosssection passenger flow in typical periods,and carries out statistical analysis on the shortterm and long-term cross-section passenger flow in the whole year.The statistical model of passenger flow data is established to realize the prediction of long-term passenger flow.(3)The operation of Chongqing Rail Transit Line 1,Line 2,Line 3,Line 6 and Shanghai Rail Transit Line 1 and Line 10 are analyzed,including line direction,size intersection,vehicle type,departure interval,etc.Based on passenger flow statistical analysis,vehicle loads are calculated and axle load frequency spectra of different graded loads are obtained.Based on Miner's linear fatigue cumulative damage theory,the equivalent axle load of short-term and long-term rail transit is calculated.The feasibility of reducing design load as fatigue design load is analyzed and verified.The standard value of fatigue design load is determined as vehicle design load multiplied by reduction factor of 0.75.(4)Relying on the two bridges of Jiahua Railway Special Bridge of Rail Transit Line 9 and Qiansimen Jialingjiang Bridge of Rail Transit Line 6,the fatigue design load of the proposed rail transit bridge is analyzed on the real bridge.From the analysis results,the fatigue design load standard is reasonable.