| At the beginning of the 20th century, it was well know to all that the cracking phenomenon of the massive concrete structures due to the heat of hydration of concrete, in allusion to the need of the constructing of great concrete dam and other massive irrigation works, a series of methods of avoiding the concrete cracking have been opened out. In the recent decades, the cracking phenomenon of concrete in foundation,bridge,lining bricks or stones of tunnel and other normal structures is familiar . at the same time it is found that shrinking induced by dryness is not very important.the heat of hydration and the variation of temperature have become the main reason resulting in restriction stress and cracking between plain concrete and reinforced concrete. the project studies the several cracks appearing during the construction of the Songhua River Great Bridge at nine station in Jilin province, in order to study the reasons of cracks appearing , some meaning research has been done in simulation calculation, we gain the conclusion that the main reason of cracking of this bridge is lead by heat of hydration, basing on this we simulate the forepart temperature field and the stress field with the finite element method .With the I-deas we process the emulational calculation of the forepart cracks of the Great Bridge Songhua River, in the first chapter we expatiate the distributing of temperature in the concrete structures and some influencing reasons and the effect of temperature is discussed, then we discuss the form of cracks in concrete and the cracks of temperature and find that it accounts for about 80 percent for all the cracks in concrete structures, next we discuss the recent research in the stress of temperature, deformation and cracks of temperature about the concrete structures . at last explain the background of the subject and main work.During the calculation of the early age temperature field, the early age physical and mechanical performance of concrete varies with its age, therefore in the second chapter we discuss the early age physical and mechanical performance of concrete and its development regulation with time, we emphasize elastic module and the development about the early age strength of concrete varying with time, at the same time consider the effect of shrink and creep upon the early age of concrete, in succession discuss how to confirm the physical parameter of thermodynamics of concrete.In order to solve the early age temperature field of concrete with the finite element method accurately, we discuss the finite element method about solving the temperature field in the third chapter. First expatiate the differential equation of heat exchange, then confirm the boundary condition. Because we use variational principle to educe the formulas about the temperature field ,in the second section narrate the variational principle and list three methods about solutions of transient temperature field and decide to use backwards difference to solve the early age temperature field of the number 0# of the box girder in the fourth chapter. The thermal cracks of concrete structures involve many factors, in the fourth chapter we adopt I-deas to simulate the temperature field and stress field of the number 0# of the box girder of the Songhua River Great Bridge at nine station in Jilin province. to the temperature field we mainly consider the temperature rise due to hydration heat ,inside and outside difference in temperature and concrete block dissipating heat toward outside. The stress field includes the effect of gravity and temperature upon the early age temperature field of concrete with time. Think over the result we can see the change in temperature of the early age concrete structures will make the concrete structures distort, if the stress induced by distortion exceeds the temporal the limit of concrete strength, the concrete will crack. from the analysis we can gain the conclusions:think over the geometrical shape of the box girder in the fourth chapter, we can see it is reasonab... |
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