Research On Temperature Field Test And Temperature Effect Theory Of Concrete Box Girder

Due to the poor thermal conductivity of concrete, the structure will form a largerthermal load by solar radiation. Thermal stress produced by the thermal load is one ofthe important factors that result in the crack of the concrete box girder. Because of thecomplexity of concrete heat transfer problem, the theory and calculation method abouttemperature effect has certain defects during the design of concrete bridge. Thesimplified calculation model and method can make the value of the thermal load andthermal stresses appear larger error. This paper does an in-depth research on thetemperature field and its effect of concrete box girder by solar radiation, with improvingthe calculation theory and methods, analyzing and discussing the value of thermal load.Based on the Xing Fuyuan Reservoir Bridge in Guilin double bridge, this paperselects the single chamber box girder section of the bridge’s continuous rigid frameperiod as the research object, has made the following research:（1）The temperature field test instruments and method of the single room boxgirder measurement are illustrated. By analyzing the measured data of temperature fieldunder continuous hot weather, the characteristics of temperature field about roof, webplate, and bottom plate of the box girder are put forward.（2）The mechanism of heat transfer is studied between the concrete box girder andthe external environment. And the sunshine temperature field’s boundary conditionssystematically are explained. The sunshine numerical calculation model of temperatureresponse which can satisfy the complex boundary conditions of concrete box girder isestablished.（3）This paper collects and analyses the sunshine temperature distributioncalculation analysis method of concrete single box girder which assumes that thetemperature distribution along the concrete wall thickness direction has aone-dimensional periodic characteristic. And through to the traditional one dimensionheat conduction differential equation numerical solution, the analytical solutionexpression of wall temperature field inside that is in the form of Fourier series is got.Only it takes a few of the analytic solution in the application that can get enoughaccurate results.（4）Through analyzing the measured temperature data, the most adverse thermalload of concrete box girder under solar radiation which is suitable for the region is obtained, and comparison with Chinese railway concrete bridge design code on thermalload, suggestions for thermal load values are proposed.（5）The theoretical calculation method of thermal stress on concrete box girderstructure is studied. The analytical method converts a three-dimensional problem into atwo-dimensional plane problem, and considers the coupling effect between the stresscomponents caused by Poisson Effect. Using structural mechanics method can berealized in the actual calculation considering the coupling relationship between stresscomponents of three dimensional space of thermal stress analysis. Combining with theengineering background data in this paper, the result’s accuracy of the calculationmethod compared with the traditional calculation method has improved significantly.（6）Causes of temperature cracks are analyzed in detail, and the correspondingcontrol measures are presented according to the causes of the formation of cracks in thedesign phase and construction phase of bridge.