Research On Temperature Field And Temperature Effect Of Concrete Box Girder In Large Temperature Difference Area

With the rapid development of society,bridges have played a pivotal role in China's basic transportation construction.The effect of temperature on the bridge structure is no less than the influence of dead load or live load,which is one of the main causes of cracks in the construction and operation of the bridge.China has a variety of climate types,and the temperature effects of bridges vary under different climatic conditions.Among them,the temperature field distribution of the concrete box girder bridge in the large temperature difference area has its uniqueness,and the temperature effect caused by the large temperature difference is more obvious,which brings great hidden danger to the durability and safety of the box girder bridge structure.Therefore,it is of great significance to study the temperature field and temperature effects of long-span concrete box girder bridges in large temperature difference areas,and to reveal the distribution characteristics of temperature gradient and temperature stress of concrete box girder in large temperature difference areas.Based on the engineering background of a Yellow River Bridge in Shanxi Province,this paper conducts theoretical and numerical simulation studies on the construction and service environment with large temperature difference between day and night and season.The main work and conclusions are as follows:(1)The finite element analysis software ANSYS was used to analyze the temperature field of the background bridge under the sunshine condition,and the temperature gradient distribution law in accordance with the climatic conditions of the region was obtained.The thickness of the box girder(top plate thickness,web thickness,floor thickness,box)The height of the beam and the value of the thermal parameters of the concrete are taken as variables to study the parameter sensitivity of the temperature field distribution of the box girder;the analysis results of the two-dimensional box girder section and the threedimensional box girder section are compared,and the analysis model is used to analyze the temperature field of the box girder.influences.The research shows that the highest temperature of the outer surface of the roof appears at around 14:00,and the highest temperature of the web and the bottom plate appears at around 16:00.The cross-section size of the box girder has little effect on the temperature field distribution,but the thermal conductivity of concrete Larger,the larger the thermal conductivity,the more stable the distribution of the temperature field of the box girder and the smaller the cross-section temperature difference;the temperature field distribution of the concrete box girder bridge obtained by the two-dimensional and three-dimensional model analysis is almost the same,indicating two-dimensional The analytical method has good adaptability.(2)Based on the analysis results of the box girder temperature field,the thermo-solid coupling analysis is carried out to investigate the temperature stress distribution law under the two different conditions of daytime and cooling night with the highest solar radiation intensity,and the overall time-varying law of the box girder stress is obtained.And the stress variation law of each member;the two-dimensional box beam section and the threedimensional box beam section model are used to compare the distribution law of box beam temperature stress,and the calculation error of different modeling methods is verified.The research shows that during the day when the temperature rises,the lateral tensile and compressive stress of the inner and outer surfaces of the box girder are much larger than the vertical tensile and compressive stresses;the transverse and vertical compressive stress of the web and the bottom plate are more than horizontal.Vertical tensile stress;on the night of temperature drop,the lateral stress of the box girder and the bottom plate are more than the vertical stress,and for the web,except for the vertical tensile stress of the outer surface,the variation is larger.The horizontal and vertical stresses are not much different;in addition,the stress results of the three-dimensional model are slightly larger than the stress results of the two-dimensional model.(3)Through the hydration heat analysis of the box section 1# of the cantilever construction process,combined with the material properties of the concrete and the corresponding hydration heat release empirical formula,the box girder segments are studied at certain time points during the cantilever pouring construction.Temperature field and temperature stress distribution characteristics;based on the variation law of concrete tensile strength,measures and suggestions on how to prevent cracks in box girder during construction are proposed.The research shows that under the action of hydration heat,the time nodes corresponding to the maximum temperature and temperature tensile stress of each structure of the concrete box girder are different,and the time node corresponding to the maximum temperature tensile stress usually lags slightly behind the time corresponding to the temperature maximum.Nodes,but all before the third day of the suspension.