Thermal Stress Study Of Hydration Heat Of Thick-Walled High Pier

Damage to concrete bridge starts from cracks. That designs were unreasonable led to bridges'destruction before computer and theory of finite element invented. After computer and theory of finite element invented,cracks appeared in most of the construction stage because construction methods were incorrect,or conservation measures are not in place.Concrete will release a large of concrete hydration heat from pouring to the next week, and gradually reducing the heat rate .At the same time, from the beginning of pouring concrete, the temperature gradually increased, concrete and ambient air temperature gradient gradually increased, the concrete and air through the convection to transfer heat, with the passage of time, the temperature gradient between the concrete and the air also decreased. Concrete internal temperature was non-linear distribution, from the inside out, the temperature distribution of high to low。Because that substances expand when heated and contract when cooled ,temperature changes will cause the volume increasing or reducing. As a result of non-linear temperature distribution, as well as the concrete role of the internal constraints or external constraints, volume deformation will cause thermal stress.Based on the analysis of concrete hydration heat, study the law of temperature field and stress field of thick-walled high pier of early concrete so that the use of concrete construction. Here are the main contents of this article:1) In this paper, starting with solid heat conduction equation on an analysis of the basic relationship between the initial conditions, four types of boundary conditions, the temperature field analysis method, described in detail the popular finite element method.2) thermal analysis of the primary task is to determine the thermodynamic parameters necessary. I measured and experience through on-site algorithm to determine the concrete heat rate, thermal conductivity, convection coefficients.3) an analysis of measured data found that the law of temperature field in heat of hydration; through the thermodynamic parameters to be determined , simulating hydration heat; simulation analysis compare to measured data4) From three aspects (amount of cement ,varieties of cement, mold temperature)affecting the center temperature of the concrete to get specific data to impact center temperature of concrete; through three surface conservation measures (water conservation and laying sand, plastic foam folder) to get specific data to affect temperature gradient between inside and outside for use in concrete construction.5) In the process of thermal analysis of concrete hydration, its material properties are rapidly changing. In this paper, the incremental method to calculate the stress of concrete creep stress and found the law of stress field of concrete。water conservation not only affect the concrete temperature, also affect the stress field.Through the above analysis, we can get the following conclusions:1) Hydration heat of concrete led to an internal temperature above 50℃. The internal temperature slowly decreased and the surface temperature decreased rapidly and the temperature Difference between inside and outside temperature is gradually increasing under convection2) Reducing the amount of concrete, using the low hydration heat of cement, reducing the pouring temperature can effectively reduce the maximum temperature of concrete center. Water conservation, Shop dry sand, plastic foam can be affixed to reduce the temperature difference between inside and outside the concrete.3) thermal stress of concrete hydration heat in about 48 hours after pouring reached maximum and then gradually decreased, the reason is that a large of hydration heat released in 48 hours after pouring concrete, resulting in volume expansion, leading to surface tension stress. Water conservation can effectively reduce the temperature difference between inside and outside the concrete and maintain that internal and external temperatures are constant after 40 hours, so it can be very effective in reducing the temperature difference between inside and outside concrete and reducing hydration heat stress.