Temperature Effect Analysis Of Steel Box Girder Based On Measured Temperature Field

With the increasing development of bridge construction in China,steel structure is widely used in constructing long-span bridges.In the design and construction process of the steel box girder,the influence of temperature load on the structure has been focused on.The temperature effect will cause temperature deformation of the bridge structure exposed to the natural environment for a long time,which will cause large temperature stress and affect its safety and stability.Especially for the unpaved steel box girder in the construction process,the temperature effect is pronounced.Because of the trend of each bridge,the climate,temperature,wind speed,and the form of the main beam section at the bridge site are different.It is not easy to calculate the temperature field distribution and temperature effect of the main girder section in the design work.The temperature effect specifications of steel box girder bridges at home and abroad are very different,which do not apply to the actual situation of different bridges.In this paper,the temperature field test of the real bridge is carried out with the east-west trending Linyi Yellow River Bridge as the background project.The measured temperature data of the typical date are selected for analysis.The steel box girder’s temperature variation law and distribution characteristics are discussed,and the most unfavorable temperature gradient distribution function is fitted.The finite element software is used to analyze the temperature field distribution and temperature effect of the steel box girder section and the structural response caused by the temperature effect of the main girder under different conditions.The main contents are as follows:(1)Through the long-term monitoring test of the temperature field of the real bridge,the measured temperature data of the steel box girder section on the typical date(different seasons and weather conditions)within one year were selected for temperature field analysis.It is found that the temperature change trend of the steel box girder section is roughly the same as that of atmospheric temperature rise and fall.When the winter temperature is low,the temperature distribution of the top and bottom plates of the steel box girder and the vertical temperature distribution of the webs on both sides are relatively uniform,and there is no evident temperature gradient.When the summer temperature is high,there are apparent temperature gradients in the transverse and vertical directions of the steel box girder section.The transverse temperature gradient is more significant,and the temperature effect cannot be ignored when analyzing the temperature effect.The temperature distribution characteristics of steel box girders under different weather conditions are different due to different solar radiation intensities.The most unfavorable temperature gradient will appear on the steel box girder cross section in the weather environment with high temperature and high solar radiation intensity.The gaussian function is used to fit the transverse temperature gradient,and the exponential function is used to fit the vertical temperature gradient.(2)According to the trend of the bridge,the geographical location and climate of the bridge site,the calculation method,and the thermal parameters of the sunshine analysis parameters needed to solve the solar radiation model are summarized.Two typical dates with the most unfavorable vertical and horizontal temperature gradients are selected to establish the solar radiation model.The reasonable boundary conditions required for the finite element analysis are obtained.The ABAQUS finite element model is used for analysis.The calculation results are compared with the measured data to verify the rationality of using the finite element model to analyze the temperature field distribution.The sensitivity analysis of the parameters affecting the temperature field shows that the radiation absorption rate significantly influences the temperature field more than the wind speed and the radiation rate.Under the action of the temperature gradient,there is obvious deformation in the middle of the top and bottom plates of the steel box girder,and there is evident stress concentration in the middle of the top plate,the web,and the connection between the top and bottom plates.(3)The Midas Civil is used to establish the main girder model,and the temperature effects of the main girder in the maximum cantilever state and after the jacking are analyzed under the most unfavorable temperature gradient and system temperature change.It is found that under the most unfavorable temperature gradient,the main girder will produce apparent displacement,internal force,and stress changes;the transverse temperature gradient significantly affects the transverse deformation and stress of the main beam.The longitudinal deformation of the main beam is significant under the change in system temperature.The bearing offset has a linear relationship with the system temperature change,and the slope of the linear change is roughly the same.A certain bearing pre-offset should be set to prevent the eccentric compression of the pier.