Research On Reinforcement Arrangement Of The Directly Embedded Spiral Case Of Right Bank Power Station Of Three-Gorges

There are three kinds of spiral cases, including the cushion layer form, the preloading filling form and the directly embedded form. Among the three forms mentioned above, the directly embedded spiral case has a good perspective in application with the characteristics of convenient construction and steady working performance of the hydraulic turbine generator unit. However, this form is not widely used due to the difficulty to control the outer concrete cracks.In this paper, the equivalent uniaxial constitutive model of concrete in axial symmetry is deduced, and the correspondent module is added to the original computer program. Then the computer program of axial symmetry nonlinear FEM of reinforced concrete is used for the research on carrying capacity and crack control of the directly embedded spiral case of the right bank power station of Three-Gorges, which is the largest directly embedded spiral case in the world. The main results are as follows:(1) The spiral case in Three-Gorges is designed based on non-pressured pipe flow. It is not necessary to make the calculations of carrying capacity, and it is enough only to check its serviceability limit state to control the width and length of cracks.(2) The larger the gap between spiral case and outside concrete, the smaller the stress in outside concrete and the larger the stress in spiral case and the rate of carrying capacity.(3) When the value of HD, the thickness of outside concrete and the reinforcement are all fixed, the following conclusions are obtained: â‘  The rate of carrying capacity of spiral case will become larger when the diameter of the spiral case and the distance between the center of circle of case and the center line of the unit become smaller proportionally, and the cracks tend to be controlled easily. â‘¡ The rate of carrying capacity of the spiral case will become larger when only the distance between the center of circle of case and the center line of the unit becomes larger or only the diameter of the spiral case becomes smaller. â‘¢ Only decreasing the distance between the center of circle of the spiral case and the center line of the unit or only increasing the diameter of the spiral case can restrain the development of cracks.