The Study Of The New-style Double-layer Combined Steel Penstocks

Underground penstock is widely used in water power stations of middle or large scale. But with the water pressure and the penstocks diameter become larger, the traditional penstocks design is not applicable. A new-style double-layer combined steel penstocks is proposed in this paper. The lined steel ring and concrete ring of the new design can work effectively and the deformation of the two lined tube compatible.Based on the elastic theory of thick-cylinder and the condition of deformation compatibility in radial, an analytic formula is deduced to describe the interaction among the inner lined steel, outer lined steel and surrounding rock to share internal water pressure. A new method is proposed by combined analytic method and finite element method, in which the lined concrete ring of the new structure is designed to subject the main external pressure and its critical plastic external pressure is also deduced, applying the theory of thick-cylinder. Based on much systemic numerical tests, the design principle of this new-style penstocks is proposed in this paper and two typical examples are analyzed in order to compare with the traditional steel penstocks. The examples also show when internal and external pressure are both large enough, especially external pressure becoming the key of the design, this new penstock shows much better bearing capacities such as: enhanced the stability of steel penstocks under external pressure much better than traditional lined measures, e.g., setting alar planks or stiffening rings; through using lined concrete to bearing external pressure, lined steel thickness is reduced greatly, and load-bearing ratio of rock to lined steel is obviously increased.