Investigation Of Performance Under Loads And Calculating Methods Of Prestressed Concrete Penstock

Recent years, with the full-blown development of the prestressed concrete technique, the prestressed technique with ring-like strands as the professional technique adapted to the penstock, has been applied to many civil engineering fields such as tunnels and surge shafts in civil engineering hydraulics and power engineering, containment shells of nuclear power station, industrial storage bunkers, digesters and conservation pools in municipal engineering. Now the prestressed concrete penstock with ring-like strands has been attached more and more importance and has been done many significant studies.Combined with the hydraulic technique key project of Ministry of Water Resources: Research on Loading Behaviors and Design Methods of Perestressed Concrete Penstock (SZ9422) and the Three Gorges construction research project: Design and Analysis of Prestressed Concrete Penstock with Steel Liner in the Three Gorges Power Station, several main tasks have been done as following.1. According to the principle of ring-like strands operation, the mechanical analytic solution of presressed concrete penstock under the uni-ring-like radial loads is given out based on the theories of elastic footing beam. The checking methods of prestressed concrete penstock during construction stage are suggested. The formula is proposed to calculate the maximum distance of two consecutive strands to be result in uniformly distribution of concrete prestressed along the penstock. The tensile steps and the tensile forces during construction stage of prestressed strands are confirmed for decreasing the secondary bending moment along the axial of penstock.2. The formulas of internal forces of prestressed concrete penstock with or without steel liner are given based on the elastic plane strain theory of axisymmetric multilayer cylinders and the mechanism of the ring-like strands action. According to the aim at the crack control and the ultimate bearing resistance, the methods are given out for checking the normal serviceability and designing the ultimate bearing resistance of the penstock.3. Combined with the full scale models tested in-situ of prestressed concrete penstock with double circle unbonded strands and single circle bonded strands of XiaoLangdi Multipurpose Dam Project of Yellow River, the advantages and disadvantages of two different prestressed systems are analyzed, the concrete stress distributions of the prestressed concrete penstock are induced and summarized during the whole tensioning strands stage. The consistence among the test results, the theory calculating and the three dimensional finiteelement analysis is proved. Therefore, the theoretical method of prestressed concrete penstock is feasible.4. Combined with the design of the Three Gorges prestressed concrete penstock with steel liner in the Three Gorges Power .Station, the consistence among the results of theory calculating, the analysis of plane finite element and three dimensional finite element is proved, the concrete stress distributions of the prestressed concrete penstock are analyzed with different steel liner thicknesses, different crack resistances, different concrete thicknesses and different initial radial gaps between steel liner and concrete. The feasibility of the design method of prestressed concrete penstock with steel liner is proved.