| Structural stability of arch dams is global stability among dam body, rock and their interface. It includes abutment stability, up-slide stability and structural stability of dam body etc, which is one of the important subjects in arch dam design and research. Because of the development of construction of high arch dams in China and thinner dam body with the use of optimum design, local regions of arch dams approach thin shell structure, which will lead to structural buckling. Anciently, study on dam body stress, abutment stability and up-glide stability is rather abundant by the dam engineers, but quite few on structural stability of dam body. Based on these hot and key spots in construction of high dams at present, Combining one of the 973 plan projects: Study of Global Stability of Geology Engineering System under Interaction of Several Factors(NO.2002CB412707), the dissertation mainly studies the stability anomaly and corresponding shape optimization. The main contents are as follows:The dissertation advances stability analysis method of arch dams based on arch-cantilever method, that is, the stability of arch ring and cantilever are analyzed respectively based on arch-cantilever method and corresponding formula of stability calculation is established. So the calculation methods of dam stress and stability are unified. Using the method, studies reveal that the stability of arch dam against buckling is generally governed by the top arch ring and the cantilever is more steady than the horizontal arch.Based on the statistic analysis of the geometric parameters of numerous high thin arch dams, the simulation models of typical arch dams for spatial stability analysis are established. The effects of some factors such as: geometric characteristics, stress state, boundary conditions etc on dam stability are analyzed and discussed. The "slenderness coefficient" is used to define the slenderness of dam body. The relation of stability and strength of arch dams are studied through FEM numerical calculation of dam stability. The "critical slenderness coefficient" is advanced and supposed to be defined as the slenderness between strength failure and buckling failure. It is used as a new standard to divide thick or thin arch dams. When the slenderness coefficient is greater than the "critical slenderness coefficient", the arch dam will maybe become instable and it is a thin one; or strength failure will take place and the arch dam is a thick one. Compared with the definition of thick or thin arch dams by thickness-height ratio, the definition by strength failure or buckling failure is more explicit in mechanical conception. For the 300 meters level high arch dams, when the slenderness coefficient is greater than the "critical slenderness coefficient", maybe the structural buckling will happen earlier and it is necessary to modify the stress criterionand take the reducing effect on stress criterion of structural buckling into account.The dissertation applies catastrophe theory to dam structural buckling study, fits the results of stability of typical arch dam by FEM, using cusp catastrophe model, estimates the stability of arch dam. It reveals that stability estimated by catastrophe theory is agree with the FEM result.Using structural optimization theory, the primary shape parameters (slenderness coefficient and thickness-height ratio) are optimal analyzed, and the minimal thickness-height ratio and the maximal slenderness coefficient restrained by dam body stability are put forward, which can be a reference for arch dam design and research. The result of shape optimization indicates that little decrease of the maximal slenderness coefficient or little increase of the minimal thickness-height ratio, that is, little increase of stiffness of dam body, will enhance the stability safety degree greatly.
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