Research On The Ultimate State And Design Method Of Steel-lined Reinforced Concrete Penstocks Embedded In Dams

Massive hydraulic structures have been widely used in practice. Because of the complexity of structural types and the multiplicity of loads, there are not acceptable methods of design up to now. The steel-lined reinforced concrete penstock embedded in concrete dam is very important to the dam. With the progress of hydraulic technology and the increase of the dam's height, the structure becomes more important. The load of the penstocks is impossible to exceed the design level in fact. A large amount of investigation and research indicate that, under the design load, concrete is far away from cracking entirely while steel-line and reinforced steel are not yielded in the stretch area, nor is concrete crushed while steel-line and reinforced steel yielded in the press area. Therefore, the ultimate state of massive hydraulic structures can't be defined as material intensity that concrete or steel attains. The design method for bar-structures has been on this ultimate state and therefore the design method for massive hydraulic structures is behind the times. So we should research the destroy mechanism of the penstocks, and establish a new ultimate state, on basis of which to put forward a design method.With close reference to actual projects, the paper collects and analyzes a large amount of information about penstocks embedded in concrete dams, then creates the typical finite element models on the basis of the theory and the collected information. By applying ANSYS procedure with consideration of strain hardening model and on the basis of elastic-plastic theory to thewhole process analysis of steel-lined reinforced concrete penstocks, the paper defines the tensile strain state of the combined function of dam-penstock. The ANSYS results show that there is micro-crack in the part of concrete around the penstock under the design load of internal water pressure. The structure is partly in the state of plasticity. So the paper puts forward a newly reasonable definition of the ultimate tensile strain of concrete on ultimate state for the penstocks embedded in concrete dams.The paper studies the effects of different ultimate tensile strain of concrete, ratio of thickness of concrete to diameter of penstock, the reinforcement in concrete and temperature load on the tensile strain of the concrete around the penstock. On the basis of common theory about the ultimate state, a chart method is introduced to design penstock embedded in concrete dams easily and quickly, combined with the actual data and the result of analysis. By an actual instance, this paper clarifies the corresponding calculation method of reinforcement.The analysis in this paper is based on practical penstocks embedded in concrete dams. The law and conclusion can provide reference for practical engineering and theoretical research in the days to come.