Study On Fatigue Behavior And Fatigue Model Test Scheme Of Steel-concrete Composite Segment Of Cable-stayed Bridge On High Speed Railway

Hybrid girder cable-stayed bridge can give full play to the material properties of steel and concrete,and the steel-concrete composite segment used to connect the two materials is one of the key structures of this type of bridge.At present,hybrid girder cable-stayed bridges are mostly used in highway bridges in China,but there are relatively few examples in railway bridges.However,due to the more prominent live load effect in railway bridges,the fatigue performance of steel-concrete composite segment in railway bridges deserves more attention.The newly built Anjiu Railway Yangtze River Bridge in which the designed speed is 350km/h is the first cable-stayed bridge with hybrid beams in 672 m long-span high-speed railway in China.Under the condition of high-speed and high-density operation of the railway,the fatigue behavior of the steel-concrete composite segment of the main girder is the focus and difficulty of the bridge research.Based on the engineering background of Anjiu Railway Yangtze River Bridge,this paper studies and analyses the mechanical properties of the steel-concrete composite segment of the bridge under fatigue load,and optimizes the fatigue test model according to the principle of equivalent stress amplitude.The main research contents and results are as follows:1?The four-line fatigue coefficient of this paper is 2.23 based on relevant literatures and standards.The three dimensional finite element model of the steel-concrete composite segment of the Yangtze River Bridge of Anjiu High Speed Railway is established by using ANSYS.The stress distribution law of each component in the stiffness transition segment and the steel-concrete composite segment under dead load,maximum positive moment under live load and maximum negative moment under live load is mainly studied.The results show that the steel roof of the side box in the steel-concrete composite segment bears a large force,and the stress distribution range under live load maximum positive and negative moment is-20MPa~3MPa,2MPa~18MPa;The most unfavorable fatigue stress amplitudes of steel roof and concrete are 23.17 MPa and 5.05 MPa respectively.The roof region of side box is taken as the focus region of equivalent design of fatigue model test.2?According to the fatigue characteristics of the steel-concrete composite segment of the Yangtze River Bridge on Anjiu High Speed Railway,the fatigue test model is designed according to the similarity theory of model design and the principle of equivalent stress amplitude of control sections.Taking the steel-concrete interface as the stress control section,four model schemes are designed successively.By comparing the equivalence of fatigue stress amplitude under live load and considering the requirements of laboratory loading equipment,the fourth scheme of local reduce scale is selected as the final test scheme.The test model is 6m long,1m wide,0.5m high and the similarity ratio is 1:2.According to the characteristics of the model test scheme,the loading tooling and test scheme matching the test model are designed.3?Based on the fatigue test model of steel-concrete composite segment,the effects of the connection mode between steel roof and concrete,the height of end diaphragm,the thickness of roof and bearing plate on the stress of the test model are analyzed.The results show that the setting mode of end diaphragm and the bonding performance between steel roof and concrete have different effects on the fatigue stress amplitude of the welds between bearing plate and roof,and the welds between PBL and steel roof,as well as on the load transfer ratio between different plates in steel beam.The effect of roof thickness on the fatigue stress amplitude of the above welds is greater than that of the thickness of the bearing plate.