Fatigue Evaluation And Analysis Of U-shaped Steel Beam Structure Of Intercity Railway

With the rapid development of urbanization in China,intercity railway,as a new application form of rail transit,can effectively solve the problem of congestion between adjacent cities.With the advantages of high safety,low building height and low cost,U-beam has been widely used in urban rail transit in recent years.However,due to the great difference between urban rail transit and inter-city rail,there is no mature design experience to follow in the application of U-beam in urban rail transit.At present,the standard U-beams in application are prestressed concrete structures,and the span is generally no more than 30m,while the steel bridge has the characteristics of strong spanning capacity,so the design of U-beams as steel structures can better play its advantages in the intercity railway.As a new type of structure,the application of U-shaped steel beam in the whole country is still in its infancy.Accordingly,the research on the fatigue problems in the design and operation of steel bridges is limited.Therefore,the simply supported U-shaped steel beam with a span of 40m is taken as the research object to analyze its fatigue performance under the train load.The main research contents and conclusions are as follows:（1）This paper expounds the research background and significance of this paper,summarizes the application status of U-shaped beam,the research status of steel bridge fatigue,the research status of vehicle bridge coupling analysis and the status of bridge fatigue reliability analysis under the dynamic load of the train,and leads to the research focus of this paper-the fatigue performance of U-shaped steel beam under the train load.（2）The fatigue stress time history of U-shaped steel beam is calculated by train-bridge coupling dynamic analysis method.The results show that:the mode of U-shaped steel beam is mainly local vibration;the stress of each part of U-shaped steel beam increases with the increase of axle load,in which the bridge deck and bottom plate should be the focus of the subsequent fatigue evaluation;the stress at the welding part is larger than that at the non welding part,in the fatigue evaluation Attention should be paid to the fatigue properties of welding joints.（3）Based on the S-N curve method,the fatigue damage calculation and fatigue life evaluation of U-shaped steel beam are carried out,and the effects of speed,vehicle weight and main design parameters are analyzed.The results show that:the fatigue performance of U-shaped steel beam conforms to the requirements of the code,and there is no fatigue damage;the welding stress amplitude between the bottom plate and the longitudinal rib of U-shaped steel beam is high and the stress fluctuation is large,so the fatigue problem is more significant;the sensitivity of different sections to the speed,vehicle weight and main design parameters is different,In different stages,different vehicle speed,vehicle weight and main design parameters have different effects on fatigue damage.Considering this factor in structural optimization design can effectively improve the safety and economy of the structure.（4）The fatigue reliability of U-shaped steel beam is evaluated by the combination of train-bridge coupling dynamic analysis and S-N curve method.The results show that the lognormal distribution can better describe the statistical characteristics of the equivalent stress amplitude S_re and the number of cycles N;after the target reliability index is determined,the maintenance period of the key fatigue parts of the U-shaped steel beam can be determined.In the case of the same maintenance period,the larger the design parameters considered in this paper,the greater the reliability,the smaller the fatigue failure probability and the safer the U-shaped steel beam.In the case of the same target reliability,the longer the service life of the bridge will be due to the increase of the design parameters.Combined with the reliability index curve,the relatively economic structural design parameters can be obtained on the premise of ensuring the safety of U-shaped steel beam.