Early Temperature Field And Temperature Effect Of The Test Member Of A Railway Suspension Bridge Pylon In A Mountainous Area

In the construction of bridge structure,the early temperature field and temperature effect of the mass concrete of the bridge tower have always been the key factors affecting the quality of the project.Mass concrete structure has the characteristics of large geometric size and large amount of one-time pouring.Due to the poor thermal conductivity of concrete,the heat generated by the hydration reaction of mass concrete during the pouring process is not easy to dissipate.In this paper,the mass concrete of the test section of the pylon of a railway suspension bridge in a mountainous area is taken as the research object.Through on-site monitoring,the curve and law of the early temperature and strain of the concrete are obtained.The relationship between the temperature field and the strain field of the test section is analyzed,and the finite element numerical value is combined.The influence of temperature-sensitive parameters of heat of hydration on the temperature field and temperature effect is simulated and studied,and the temperature control and crack prevention measures for mass concrete are proposed.The main work is as follows:1.The necessity and significance of temperature control of mass concrete in bridge structure are expounded,the reasons for temperature cracks in mass concrete are summarized,and the development status of research on heat of hydration and temperature control crack prevention measures of mass concrete is introduced.2.Monitor the early temperature-strain field of concrete in the test section of a railway suspension bridge pylon,and by analyzing the measured data of the temperature field,the results show that the maximum peak temperature of the concrete in the test section during the heat of hydration is 61.1 °C,and the maximum temperature gradient is 16.7 °C.In the 2.5m short limb section;the maximum cooling rate of ambient temperature in Luding area in November is 4.6℃/h,and the maximum cooling rate of concrete surface is 5℃/h.3.Analyze the strain time history curve of the strain measuring points in the test section in the stage of hydration heat and after removing the formwork and insulation measures.The results show that the concrete deformation in the test section at the initial stage of hydration heat is mainly compressive strain,with a maximum value of202.7με.When the formwork and maintenance measures of the structure are removed,tensile strain is generated on the concrete surface under the action of temperature difference.The maximum horizontal tensile strain is 163.4 με,and the maximum vertical tensile strain is 122.7 με.4.The finite element model of the test section of the bridge tower is established to analyze the heat of hydration,and the accuracy of the model is verified by comparing the measured data and the finite element simulation value.Numerical analysis is carried out on the influencing factors of concrete temperature field and stress field through finite element model,including concrete material parameters,mold entry temperature,maintenance measures,external ambient temperature and pipe cooling parameters,etc.And the influence law and degree of temperature effect.5.Summarize some temperature control and anti-cracking measures that can be used in the construction of a railway suspension bridge tower in a mountainous area,including the optimal mix ratio of concrete and the selection of raw materials,the control of the temperature of the concrete entering the mold,the arrangement of the cooling water pipe,the control of the temperature difference between the core and the surface,Maintenance measures and construction control,etc.,provide reference for improving the construction quality of bridge tower mass concrete.