The Preliminary Study Of Structural Stability Of Hight Arch Dam

Structural stability of arch dams is comprehensive stability between dam body,foundation of dam and their interafee. It contains abutment stability,up-slide stability and structural stability of dam body etc,which is one of the vital subjects in arch dam design and research.There are many hight arch dam (hight of 300m level ) that buliding and would building in the south-west and north-west of china.As the increased levels of concrete and thinner dam body with the use of optimum designing, the local regions of hight arch dams approach thin shell structure,which will lead to the structural buckling. Anciently study almost on dam body stress,the abutment stability and up-slide stbaility is rather abundant by the dam engineers,but quite few on the structural stbaility of dam body. Because the hight arch whose hight is over 200m is not inclued in the Concrete arch dam design standard(2003) of china, the research structural stability of dam body is a difficult challenge for dam engineers.The dilemma of this subject is:"How thin the dam body is that arch dam should considering the structural stability?","Whether the critical flexibity confficient of arch dam which is difinited by DingXiao tang is exist ? And What's it if exists?","What's the relation between the structural stability of dam body and the stress safety of dam material?"Because this subject relates many other codition such as: the valley shape, distribution of faults around arch dam,earthquake and so on, the research of structural stability of arch dam is so difficult that the dam engineers always analysis the structural stability of hight arch dam in addtion in the arch dam designing.In this paper,we studied the tructural stability of hight arch dam by crown-cantilever method and theory of shell and FEM numerical analysis. Mainly includes the several aspects as following:(1) The trial load method of arch dam is comprehensive dicribed in this paper,and a new method called differential method which is given by FengGuang hong in 1980.Compared by actual project, we conclude that the differential method is more practical and convenient than the common crown contilever method. Beside, the displacement cofficient of crown contilever are also discussed. By actual project,we conclue that the errors of the existing cofficients of crown contilever in arch dam are less than 10%. And some of cofficients whose errors are more larger are corrected.(2) The critical buckling load of arches are researched. We conclude that the classic theory overestimated the critical buckling load of arches, and the non-linear theory is more suitable for horizontal arch buckling in arch dam. Beside, we discuss the influence of the elasic foundation and temperature load to the horizontal arch buckling in arch dam.And the empirical formula of the critical buckling load of arches which are effected by the elasic foundation and temperature load is given.(3) Base on crown-cantilever method, the mechanical properties and structural stability of the parabolic arch and circular arch are compared.And the internal forces of parabolic arch in different f/L are given. We conclude that circular arch is better than parabolic arch in mechanical properties aspact. However, parabolic arch is little better than circular arch in structural stability aspact. The effect of the internal force in arches with structural perturbation are discussed.And we conclude that the effect of the internal force in arches with structural perturbation is more sensitivity when T/B of arch is smaller than 0.03.(4) The buckling of parapoblic arches with non-uniform loads of arch dam are approximate researched by the pinciple of virtual work method. And structual safety factors of parapoblic arches in arch dam are given in this paper.(5) Base on the calculation of statistical method, the experience function of the critical cracking flexibility cofficient of arch dam which is related with the height of arch dam and ratio of the valley width to height is given. Beside, we also get the experience function of the thickness to height ratio with the height of arch dam and the ratio B/H of arch dam. Those experience function of key cofficient for arch dam is very helpful for dam engineers.(6) By the crown-cantilever method, the relations between the tructural stability of arch dam and the stress safety of dam material in the circular arch dam under different condition and level of concrete are researched. And we conclued that the safety of arch dam is dominated by the sress safety of of dam material when the thickness to radius ratio of horizontal arch in hight arch dam is larger than 0.03, and the structual stability of dam body could be ignored at that condition. However, as the stability of arch dam is related with many other complex factors and the crown-cantilever method is approximation, we should continue confirming those conclusion by 3D-method.(7) Base on the FEM numerical calculation, the experience function of tructural stability cofficient of arch dams which are related with the flexibility cofficient and dam heigh are given. Beside, we also analysis the relation between tructural stability of arch dam and other main factors such as dam heigh, thickness of dam, end-restraits and so on. And the JinPing hight arch dam and XiaoWan hight arch dam is analysised by FEM numerical method. At last, we consist that the tructural stability of arch dam should must be considered when the thickness to valley width ratio of top arch in arch dam is smaller than 0.015, expecially in the shape optinoization of hight arch dam.