Analysis And Study On Temperature Field And Temperature Stress Of PC Box Girder Bridges

Temperature stress is an important factor for the cracking of prestressed concrete box girder bridges, especially the temperature loads caused by solar radiation, which is also difficult to be analyzed and calculated. So far, there still remain big differences among the modes of temperature gradient in specifications of some developed countries. And the temperature gradient curves of Chinese railway and highway specifications are completely different.In this thesis, a series of astronomic formulas are used to simulate the effects of solar radiation on exterior boundaries of box sections. The air temperature is assumed to transform as a sinusoid. On the assumption that the inner air of the box is fully transmitted, the Oppenheimer network analysis method is applied to calculate the radiation heat transfer of the inner boundaries. Synthetically taking account of the convection and radiation heat transfer between the boundary concrete and the ambient air, and based on the Fourier Conduction Equation, a two-dimensional numerical finite element model for the temperature field of box sections is made up with the calculus of variations, as well as a method of using the existing elements to compute the longitudinal and transverse self-restricted temperature stress. According to many references, the parameters such as heat transfer coefficient and thermal conductivity are analyzed.A finite element computer program is developed in FORTRAN language based on the above theoretical models, which has certain preprocessing and post-processing functions and can be used to analyze and calculate the temperature field and temperature stress of a box section with any size at any time. The program is used to analyze the temperature effect of the 1/4 main span section of a railway continuous girder bridge over the Yellow River, and the computed outcome agrees well with the measured data. Meanwhile, the results also show that the temperature stress is very large, so the temperature effect of PC box girder bridges should be paid more attentions.With the program, the influence of the parameters such as bridge azimuth, the length of flanges, the height of webs, the thermal conductivity of concrete and the velocity of wind on the temperature effect of box sections is analyzed. The thesis draws a conclusion that: when designing, it needn't to consider the transverse conduction of box sections for highway bridges with long flanges;but for railway bridges, it should be considered, especially when they are running to north or south. The temperature gradient curve of Chinese new highway specification comes nearer the real situation than the old one, but the values of Tx and T2 may be not the same in different districts of China and should be further studied.