Temperature and Stress Fields in Hydropower House Ding Lu-jun College of Water Resource and Hydropower, Sichuan University Sichuan college of architectural technology No 4, West Jialingjiang Road, Jingyang District, Deyang City, Sichuan Province, PR China. e-mail: [email protected] Liu Yu-hong Sichuan college of architectural technology No 4, West Jialingjiang Road, Jingyang District, Deyang City, Sichuan Province, PR China. e-mail: [email protected] ABSTRACT The concrete body of hydropower house is great and its structure is complex, so the temperature control simulation research has important practical application value. Considering concrete thermodynamics parameters along with the change of age, we have simulated the concrete dam construction process and adopted the three dimensional finite element method to calculate the temperature field and thermal stress. The result showed that for the site of pouring in cold season, the method of natural warehousing watering should be taken. whereas for the site of pouring in hot season, the method of control pouring temperature and the water cooling measures of the entire region should be taken. In this way the maximum temperature and the maximum thermal stress could meet requirements of the design specifications. The research results laid an essential basis for the powerhouse dam section of Hydropower Station design, construction and temperature control. KEYWORDS: powerhouse dam section; temperature field; thermal stress; three-dimensional finite element method; construction process INTRODUCTION Mass concrete structures are widely used in water conservancy and hydropower projects, especially the construction of concrete dams. And the temperature control and temperature crack problem is perplexing the construction personnel for a long time. From 1930s to start [1], Many scholars established temperature crack control theory system, and has taken a series of measures of crack prevention, such as improving crack resistance of concrete, parting block, water pipe cooling, pre cooling aggregate, surface heat preservation, and so on. The temperature rise in the hydration heat of concrete can cause the temperature stress cracks in concrete, and then destroy the integrity of the structure, so that the durability of the concrete is decreased, and even endinger the safety of buildings. Therefore, need to take measures to solve the temperature control heat of water temperature inside concrete[2]. In this paper, the three-dimensional finite element method is used to simulate the construction process of the hydropower station. - 6731 - Vol. 21 [2016], Bund. 20 6732 CALCULATION PRINCIPLES According to the theory of heat conduction, the three-dimensional unsteady temperature field should satisfy the following partial differential equations and the corresponding initial conditions and boundary conditions [3,4]. Universal equation is: ∂T ∂ 2T ∂ 2T ∂ 2T ∂θ = α + + + (1) ( 2 2 2 ) ∂τ ∂x ∂y ∂z ∂τ where: ∂T —The change rate of temperature with time; ∂τ α —coefficient of temperature conductivity; θ —Adiabatic temperature rise of concrete. Initial condition is （ ， ， ） TT|τ =00= xyz (2) boundary conditions are: first class boundary conditions: T= Tb (3) third kinds of boundary conditions: ∂T ∂T ∂T l l + l l + l l + β (T − T ) = 0 (4) ∂x x ∂y y ∂z z a adiabatic boundary condition: ∂T l = 0 ∂n 5) where lx ， ly ， lz —the direction cosine of the boundary normal; Tb —given boundary conditions; Ta —temperature; T（xyz， ， ） 0 —given initial temperature; l —coefficient of heat conductivity; β ——surface heat coefficient. Strain increment of concrete under complex stress state includes the increment of elastic strain, creep strain increment, temperature strain increment, dry shrinkage strain increment and autogenous volume deformation increment. So there is: ∆e = ∆e e + ∆e c + ∆e T + ∆e s + ∆e 0 n n n n n n (6) where: ∆e e n —elastic strain increment; Vol. 21 [2016], Bund. 20 6733 ∆e c n —creep strain increment; ∆e T n —temperature strain increment; ∆e s n —dry shrinkage strain increment; ∆e 0 n —autogenous volumetric strain increment . GENERAL ENGINEERING SITUATION A hydropower station project to generate electricity, installed capacity of 420mw, with the maximum dam height of 79.6m, crest elevation 1820.50m, crest length 346.4m. The total amount of concrete is 1164000m3. Powerhouse dam section of large volume, complicated structure form and consider alternatives to dam safety and temperature control measures, the temperature field and temperature should force simulation research, to provide a reference for engineering design and construction. CALCULATION PARAMETERS AND CALCULATION MODEL Calculation Parameters The average temperature of the project is 22.68, the average minimum temperature is 7.47, the average annual temperature is 15.21. The dam area of the annual mean temperature is shown in table 1, the construction schedule is shown in table 2, thermodynamic parameters of concrete is shown in table 3. Table 1: The annual mean temperature of he dam area (unit: ) Month 1 2 3 4 5 6 7 8 9 10 11 ℃12 year Temperature 7.47 8.83 11.43 14.43 18.98 21.35 22.68 21.8 20.5 16.15 10.93 8.05 15.21 Table 2: Plant dam upstream hydropower station construction progress Number Start construction time Initial height(m) Terminate height(m) 1 6/1/2015 1742.9 1744 2 6/20/2015 1744 1746.5 3 6/20/2015～7/20/2015 Consolidation grouting 4 7/20/2015～8/20/201 Cubital tunnel installation 5 9/10/2015 ～1/10/2016 1746.5 1763.0 6 1/30/2016 ～3/10/2016 1763.0 1772.0 7 3/10/2016～4/30/2016 Cone pipe installation and two stage concrete, spiral case 8 5/20/2016 1772.0 1774.4 9 6/10/2016 ～2/28/2017 1774.4 1820.5 Vol. 21 [2016], Bund. 20 6734 Note: the downstream unit section, the tail water platform section starting the construction period after 20 days. Table 3: Thermodynamic parameters of dam concrete Linear Temperature Specific Thermal Hydration heat Concrete expansibility coefficient heat coefficient temperature (10-6 /℃) (m2/h) (kJ/kg· ) (kJ/m·h· ) rise ) Cushion 29.617(t0.907 − 0.46) 5.8 0.00313 0.9922 7.28 T = ℃ ℃ 0.40+℃t0.907 normal 32.05*τ Dam normal 5.75 0.00318 0.99035 7.395 T = 2.15 +τ Computational Model and Coordinate System[5,6] The calculation model for dam transverse joints between the dam and the dam axis. The overall coordinate system origin of the dam left at the dam heel. Pointing to the right bank of the dam axis is the X axis direction is positive, downstream of the positive Y axis, vertical axis is Z positive. Calculate the model in the depth direction of the dam to take 100m, the upstream direction of 100m, the downstream direction is also taken 100 m. Temperature field calculation in boundary conditions is selected: foundation bottom surface and four side and monolith joint surface is adiabatic boundary, the dam downstream face above the water level for solid-gas boundaries, below the water table for solid-water boundary. Solid-gas boundary is treated by third kinds of boundary conditions. The selection of boundary conditions in the stress field calculation is: the foundation is treated by fixed bearing, and the foundation is treated with y in the upper and lower reaches. The other is the free boundary. Plant dam model is shown in Figure 1. Figure 1: The calculation model of power building monolith Calculation Scheme The power building monolith section of the dam foundation surface elevation for 1741.9m, crest elevation for 1820.5m, dam height 79.6m, dam length for 28.6m, dam width for 76.0m. The opening time of the test concrete was June 1, 2015, and the elevation of 1820.5m was reached by February 28, 2017. Downstream unit section, the end of the water platform to start construction period of 20 days. On 5~9 month casting parts adopt water cooling measures, pipe spacing 1.5*1.5m, water temperature Vol. 21 [2016], Bund. 20 6735 water temperature in the month, the watering time for 15 days, single cooling pipe length is 250m. The pouring temperature of each program is shown in Table 4. Table 4: The plant dam pouring temperature Pouring temperature Calculation scheme Restrained zones Non-Restrained zones 1 Tp=18°C Tp=20°C 2 Tp=20°C Tp=22°C 3 Tp=22 Tp=24 ℃ ℃ ANALYSIS RESULT Analysis of Temperature Control Standards and Temperature Field Calculation Results Temperature Control Standard During the construction of large volume concrete water cement of temperature increased control of concrete pouring temperature and the highest temperature inside is the key problem of temperature control and crack prevention of dam [7-8]. The power building monolith in different parts of the large volume concrete maximum allowable temperature is shown in Table 5. Table 5: The maximum allowable temperature value in different parts of building monolith Control maximum temperature Position 11~3 month 4、10 month 5~9 month 1742.9～1763m 28~30 32~34 36 Building Normal concrete 1763～1774.4m 28~30 32~34 38 monolith >1774.4m 28~30 32~34 38 Analysis of Calculation Results of Unsteady Temperature Field The process of building concrete construction through simulation of hydropower station, the thermodynamic parameters of concrete varies with age, the simulation study on temperature field of dam, In order to analyze the variation of dam temperature field, it also draws the dam in different elevation typical point temperature curve, due to the very large amount of data, so only lists a program of 14 point temperature duration curve shown in Figure 2, the typical position shown in Figure 3. In the analysis of large amounts of data found in the highest temperature of different parts of concrete have appeared in May 2016, due to the number of data is very large, now only lists the Vol.