Research On Constuction Measure And Temperature Control For Spiral Case Keeping Constant Internal Pressure

With the development of hydropower construction in China, the capacity and dimension of hydroelectric generating unit increase constantly. The structure of preloading filling spiral case is becoming larger and more complex correspondingly, and it is widely used in large hydropower house because of its reliability. The problem of buliding reasonable simulated model of construction is standing out gradually, which becomes an important issue during the design and operation. The combined effect between the concrete and the spiral case in the whole construction process should be improved. Meanwhile, there are less research results in the transient temperature field and the creep stress of the concrete surrounding the spiral case. Thus this paper studies on the simulation of construction process, the optimization analysis for preloading value and the temperature and creep stress of a preloading filling spiral case of a large hydroelectric plant through taking the nonlinearity program ABAQUS as the numerical tool. The analytical model, methods and conclusion provide a reliable technical support and reference for the structure design and study of the hydropower house and the spiral case.(1) The simulated numerical model of a preloading filling spiral case has been carried out by finite element method (FEM) based on ABAQUS program. From the view of theoretical analysis, the applicability that the damaged plasticity model could be used to study on the numerical analysis of spiral case is analyzed. The nonlinearity of initial gap and bearing ratio between the concrete and the spiral case are researched. And then the damage of the concrete surrounding the spial case and the stress of steel bar under cyclic loading are studied. The shell-spring combin technique is used as a method of quick and simple.(2) On the basis of the static intension and the dynamic stiffness, the optimization method of selecting preloading value is evaluated. The influencing factors of transfer loading, the bearing ratio and variation of initial gap are reachered through comparing several values. The finite element method is used to calculate the dynamic characteristic coefficients of the natural frequencies. And then the influence of the damage to the safety of the structure is present from the dynamic analysis. A sensitivity analysis of surrounding rocks parameters is used to calculate the system stability. The resonance vibration theory of the powerhouse structure is used to analyze the generating unit system stability and safety. (3) The transient temperature field of the concrete surrounding the spiral case is realized from construction to operation peried. The equivalent models of numerical simulated construction are built considering the hydration heat and the cooling pipes. The influence of all kinds of control parameters is studied to the temperature differences at early period. Based on the special shape of the structure, the distribution of the transient temperature in construction and operation period is showed.(4) The temperature stress of the concrete surrounding the spiral case is analyzied by sequent couple method through introducing elactic creep model. The characteristic of the creep stress at early construction stage is studied including the surface and the interior. The rule of vertical and horizontal stress in all time and the development of temperature crack are displaied by the numerical results. The influence of the temperature to the gap between the steel liner and the concrete is presented on the response of the structure. The results show that it is significant to research the temperature effect on the gap.(5) For the structural characteristics of the spiral case, the principle and measure of temperature control are studied including the preventive effect on producing crack of the cooling pipes and the surface insulation. The sensitivity analysis of the parameters such as the time of passing through water, the placing temperature of the concrete and the surface insulation of the form are conducted for the concrete surrounding the spiral case. The paper also puts forward some suggestions about the application and development of the protective measure of controlling development of temperature stress.