Reserch Of Temperature Gradient Of Unpaved Steel Box Girder And Its Influence On The Push And Pull State

The steel box girder is widely used in the construction of suspension bridge and cable-stayed bridge because of its characteristics of light weight,high strength,high torsional rigidity and convenient construction.Because the thermal expansion coefficient of the steel box girder is large,the thermal conduction is fast and the distribution of temperature field is very complex.As a hyperstatic system,the temperature effect of cable-stayed bridge is significant,and the influence of the structure is not negligible.The completed bridge state of the cable-stayed bridge tends to be different from the design state due to the temperature effect,especially when the steel box girder is not covered by the pavement in the construction process,the temperature effect is more significant.The temperature gradient mode of the steel-mixed composite beam section given by chinese standard is not applicable to the unpaved steel box girder,and it is very important to study the temperature gradient of the unpaved steel box girder.Taking the Fourth bridge on the Tuojiang river as the engineering background,the temperature field of unpaved steel box girder was monitored for three months during the construction process.Based on the monitoring data of temperature field,the rule of time change of steel box girder is analyzed.According to the theory of heat conduction and finite element theory,ANSYS is used to calculate the temperature field of steel box girder during construction.The influence of temperature gradient on structure of steel box girder pushing and pulling state is studied respectively by Midas/Civil.The main research contents and results are as follows:(1)the method of determining the sunshine parameters of the steel box girder and the method of selecting thermal parameters are described,and the comprehensive heat transfer coefficient(h)of the steel box girders and the comprehensive atmospheric temperature(Tsa)are obtained according to the method described.(2)the temperature field calculation model of the unpaved steel box girder was established by using ANSYS for the third boundary condition(known comprehensive heat transfer coefficient(h)and the comprehensive atmospheric temperature(Tsa)).On this basis,the influence of parameter changes on the temperature field of the steel box girder was studied.(3)long-term monitoring of the temperature field of the unpaved steel box girder was conducted to analyze the rule of temperature field of steel box girder over time;The temperature field distribution of steel box girder along the transverse bridge and vertical direction in different weather is given.By comparing the measured temperature with the theoretical calculation,the accuracy of the theoretical calculation is verified.(4)according to the temperature field of steel box girder at different moment,the most unfavorable temperature gradient mode of steel box girder is determined.(5)analyze the influence of the temperature gradient of the unpaved steel box girder on the thrust force of the steel box girder,and determine the influence of the temperature gradient on the stress,linear,counterforce and closing width of the steel box girder.(6)the temperature effect of the cable-stayed bridge caused by the fitting temperature gradient mode of the unpaved steel box girder and by the temperature gradient mode of BS5400 is compared,and the stress,displacement and cable force of the steel box girder are compared.