تجزیه و تحلیل شبیه سازی تنش حرارتی سدهای RCC با استفاده از المان محدود 3-D نقل مکان روش مش
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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Advances in Engineering Software, Volume 32, Issue 9, September 2001, Pages 677–682
The 3-D finite element relocating mesh method is developed for simulation analysis of temperature and thermal stress distribution in a roller compacted concrete dam during the construction period. According to the relation between specific properties and age of concrete, some meshes are merged into a larger mesh or a few larger meshes when the age of the concrete is appropriate. Using this method, the total number of elements and nodes were remarkably reduced when the dam height was increased. When the change in elastic modulus, creeps and hydration heat is within the limits permitted by design criteria, the relocating of mesh will start. Using this method, a 3 D simulation analysis of thermal stress in a roller compacted concrete (RCC) high dam can be realized by microcomputer and appeared at the construction site. On the basis of real factors during the construction period, an engineer can predict the distribution of temperature and thermal stress in the RCC dam. Therefore, engineers can take appropriate measures to control the concrete temperature to reduce the thermal stress and avoid crack development within the dam.
During the construction period of a roller compacted concrete (RCC) dam, the thickness of each layer is usually 0.3–0.5 m. Hence, an RCC dam with a height of 200–300 m may consists of several hundreds up to thousand layers. The heat will be exchanged between the top surface of a new placement layer and the circumference, and between the bottom surface and the old layer or base rock. Since the gradient of temperature and the stress in an RCC dam is great in the vertical direction, when calculating thermal stress in the dam during construction period, the mesh sizes of the region has to be 0.3–0.5 m in order to reduce the calculation error. The size of the mesh is usually same as the thickness of the layer. After generating the mesh, it is very difficult to carry out a 3 D finite element simulation analysis by a microcomputer due to the great number of elements and nodes . When the thermal stresses in the Three Gorges Project (TGP) concrete gravity dam were studied in 1989, a kind of element having two layers or several layers was developed . On the basis of this principle, the relocating mesh method is developed in this paper. Using the relocating mesh method, the 3 D simulation analysis of the thermal stress in a high RCC dam can be completed by microcomputer and performed at the construction site.
نتیجه گیری انگلیسی
The 3 D analysis of the temperature and the thermal stress in RCC high dam can be carried out using microcomputer according to the thin layer placement construction plan. If the time for starting relocation of the mesh is suitable, the error caused by relocating the mesh for temperature and stress distribution is controlled within the limits permitted by design criteria. This method, for the 3 D FEM simulation analysis of multi-layer concrete structure at a high RCC dam using microcomputer, is appropriate and can be applicable in engineering design. The simulation analysis of the temperature field in the dam during the construction period suggests that when the RCC placement temperature is the average air temperature, the highest temperature of the dam is 36.0°C; when the RCC placement temperature is controlled at 15°C, the highest temperature of the dam is 29.2°C. It is concluded that reducing the RCC placement temperature is a very useful method for controlling the highest temperature in the dam. By changing the starting date and construction plan, the temperature field in the dam is changed, then simulating the different construction programs, a better RCC construction plan can be determined. The simulation analysis of the thermal stress, considering the creep of concrete, shows that the stresses around the surfaces of the dam are greater than in other areas, and then change with the air temperature as well. When the air temperature increases, the compressive stresses will occur. When the air temperature decreases, the tensile stresses will occur. The maximum tensile stress is 1.92 MPa in this case. The tensile stresses inside the dam are lower than 0.7 MPa whether RCC placement temperature is the average air temperature or RCC placement temperature is controlled at 15°C.