Study On Temperature Field And Its Effect Of Railway Steel-Concrete Composite Beam Under Complex Thermal Boundary Conditions

Steel-concrete composite beam has the advantages of light weight,high bearing capacity,excellent dynamic performance and outstanding economy,and it is easy to lay ballastless track on concrete deck slab.In recent years,it has been widely used in railway bridge construction.Because the heat transfer coefficient of concrete is about 1/50 of that of steel,the change of ambient temperature can lead to obvious temperature gradient in the cross section of steelconcrete composite beam,which will cause concrete cracking,excessive beam deformation and bearing displacement,and affect the safety and durability of bridge construction and operation.To master the temperature field and effect law of railway steel-concrete composite beams,this paper carried out indoor model test,numerical model development,daily cycle temperature analysis and so on.The main research contents and achievements are as follows:(1)The railway steel-concrete composite beam specimens considering different track structures are designed,the ambient temperature,external radiation and wind speed are strictly controlled,and the sudden cooling and radiation heating tests are carried out.The temperature of each point of the specimens,the radiation intensity of the top surface and the slip of the steel-concrete interface are tested,and the temperature field and its effect law of the railway steel-concrete composite beam under different ambient temperature effects and wind speeds are revealed.(2)The transient nonlinear thermal analysis model of steel-concrete composite beam is established by ABAQUS,and the nonuniform film coefficient which varies with the sink and surface temperature is calculated through the secondary development of user subroutine FILM.The model is used to calculate the cooling and heating conditions of the temperature field test.The results show that the numerical simulation values are in good agreement with the model test values,which verifies the reliability and accuracy of the numerical analysis method and provides a reliable tool for daily cycle temperature analysis.(3)The theoretical model of solar radiation and ambient temperature in daily cycle is established.On this basis,the thermal-stress coupling analysis of railway steel-concrete composite beams is carried out,and the laws of temperature change,temperature distribution and temperature effect change of railway steel-concrete composite beams in daily cycle are mastered.It is found that the cross-section temperature difference will lead to the tensile stress of concrete slabs of composite beams that can’t be ignored in engineering and the deformation that affect the normal use of railway bridges.The influence of environmental wind speed,concrete slab thickness and track structure thickness on the temperature field and its effect of composite beam is also discussed.Among them,wind speed will affect the vertical and transverse temperature difference of composite beam,while the thickness of concrete slab and track structure only affects the vertical temperature difference but has little effect on the transverse temperature difference.(4)Based on the model test,combined with daily cycle temperature analysis and parameter analysis,four typical temperature action modes suitable for railway steel-concrete composite beams are put forward: daytime vertical temperature difference mode,nighttime vertical temperature difference mode,daytime transverse temperature difference mode and nighttime transverse temperature difference mode.Among them,the manifestations of vertical temperature difference mode are different before and after the construction of track structure,and the manifestations of daytime transverse temperature difference mode are related to the side of direct sunlight.Finally,the temperature difference curve is fitted,and the fitting result is compared with the domestic and foreign codes and related research to verify its rationality.