Elastic Iterative Method And Its Application In Ultimate Bearing Capacity Analysis Of Steel Lining Reinforced Concrete Penstocks

The steel lining reinforced concrete penstocks (SLRCP), as a new type of diversion system in hydroelectric power station, has many advantages, and has been used in some projects, such as the Three Gorges hydroelectric station, Lijiaxia hydroelectric station, Jin’anqiao hydroelectric station, Dongjiang hydroelectric station, Jinghong hydroelectric station, and so on. The SLRCP commonly with a higher HD (Head x Diameter) value, is constituted with inner steel lining and outer reinforced concrete wall, and is operated with crack in practice. Therefore, to assure the structural safety of SLRCP during all its life cycle is necessary.Ultimate bearing capacity (UBC) is often employed in safety evaluation of a structure as an important parameter. Many researchers focus on the computational method of UBC, and have proposed some procedures. In those numerical procedures, a method named elastic modulus adjustment method is proposed at the end of the1980’s. For its simplicity and practicability, this method is then widely used in UBC analysis of pressure vessel and pipe. However, when it goes to civil and hydraulic engineering structures, some other problems will be faced while using the elastic modulus adjustment method. Hence, Yang presented the elastic modulus reduced method (EMRM), in which the concept of element bearing ratio is proposed, and a threshold is defined based on the uniformity of element bearing ratio for reduction of elastic modulus of elements with high bearing ratio, and the elastic modulus adjustment strategy is constructed in terms of the principle of strain energy conservation. The plastic failure mechanism and the UBC of complex civil and hydraulic engineering structure can be well obtained by using the EMRM.In this thesis, some research work has been done based on team work:(1) The applicability of curved beam model of limit analysis is evaluated based on the investigation of structural internal force distribution. Then, a optimization method of steel arrangement of steel in SLRCP is proposed by using the curved beam model.(2) The EMRM has been employed successfully for obtaining the UBC of SLRCP by defining a valid element bearing ratio considering the failure mechanism of the penstocks.(3) An elastic iteration method combined the elastic center method (ECM) with EMRM is presented for acquiring the UBC of SLRCP, in which the former is used to provide internal force, while the latter is used to provide optimization algorithm.(4) The UBC of those SLRCPs, with two typical flaws of the corroded reinforcement and local thinned lining, are analyzed using the EMRM proposed, and some useful conclusions are drawn.