Research Of Temperature Field & Temperature Stress Of PK-Section Concrete Box Girder By Solar Radiation

The nonlinear thermal gradient exists in concrete box girder due to solar radiation, which would lead to considerable stress when the deformation caused by it is impeded by constraints in and outside the structure. On one hand, studies of temperature field& temperature stress caused by solar radiation have been made on ordinary concrete box girders except for the PK-section concrete box girder. On the other hand, our current specifications give no thermal gradient value on concrete girder without pavement, neither the calculation method of transverse temperature stress on concrete girder. Based on Maanshan Yangtze River Expressway Bridge, this paper carries out filed test and modeling analysis of temperature field of PK-section concrete box girder by solar radiation and calculates the girder's maximum vertical and transverse temperature stresses which are compared to the specification. The main research content and results are as follows:(1) This paper introduces the general form of the concrete's heat conduction differential equation and boundary conditions, deduces the calculation formula through simplifying the mixed boundary conditions into the third kind boundary condition and discusses the calculation process of solar radiation, heat transfer coefficient, and absorption rate.(2) By the test and analysis of temperature field of PK-section concrete box girder by solar radiation in the construction stage and operation stage, this paper provides the variation regulation of temperature in roof plate, web plate and bottom plate, the vertical thermal gradient and the air temperature in and outside the box, as well analyses the effect of asphalt concrete pavement on temperature field of concrete girder. The result indicates that the 12 cm pavement of this bridge has obviously weakened the temperature filed of the girder.(3) ANSYS is adopted to build the 2D and 3D model of temperature field of PK-section concrete box girder, and the calculating results agree well with the measured values. It's practicable to analysis the temperature field by using 2D model for the calculating results of2 D and 3D model are almost the same. Worst vertical thermal gradient modes in construction stage and operation stage are presented with exponential functions, which are compared to the modes specified by code of different countries.(4) Sensitivity analysis of model parameters shows that both the absorption rate andwind speed have large effect on the thermal temperature filed. Besides, the thickness of asphalt concrete pavement has obvious effect on vertical thermal gradient of concrete box girder.(5) The results of transverse temperature stress calculated by 2D and 3D model respectively indicate that the result of 3D model is 22 percent larger than 2D model.Comparative analysis shows that the maximum tensile stress and compressive stress in construction stage are larger than operation stage.(6) The girder's maximum vertical temperature stresses in both construction stage and operation stage are calculated by finite element software FBR.CAL, and the stress in construction stage is larger than operation stage. The calculating results of vertical temperature stress indicate that it's inaccurate to use the temperature gradient model of concrete girder with concrete pavement given by highway bridge regulation to calculate temperature stress in construction(without pavement). Therefore,it is necessary for highway bridge regulation to add the thermal gradient model on concrete girder without pavement.