Strength And Limit Load Analysis Of Concrete Arch Dams

Stress analysis method, material strength theory, safety index and design criteria are main contents in strength design and computation of structures. As for the concrete arch dams, with the increasing of height, the classical strength design theory does not meet the needs of engineering practices. In this thesis, the FEM stress analysis and strength design criteria, multi-axes strength theory and computation, limit load analysis method of arch dams are concerned.The principle of FEM equivalent stress method, with introducing of the ideas of stress classification and equivalent linearization method in 'design by analysis' for steel pressure vessel, is further developed. After analyzing 5 typical arch dams by FEM equivalent stress method, new design criteria based on FEM-equivalent stress analysis are proposed, in which the importance or grade of the structure is considered in the compression stress criterion, and as a control of tension field cross dam thickness, the limit of ratio of maximum tensile stress to the compression stress on the same section is included in the tensile stress criterion.After summarizing the present definition of the factor of safety, a new definition, by failure point and safe instance, is presented, which is suitable for any loading condition, stress state and strength theory. An effective iteration algorithm is presented for the calculation of new factor of safety. As an example, the contour of the point factor of safety considering multi-strength effect of an arch dam is calculated, in which the great difference between the multi-axes and single-axis strength is discovered.A FEM formulation of 3D lower bound limit analysis is developed for isoparametric element discretization. The stepped Newton algorithm by K. Krabbenhoft and L. Damkidle (algorithm I) is improved as a sub- iterative Newton algorithm (algorithm II), in which the traditional displacement FEM program can be used, so the so-called dimension hinder in 3D problem is avoided , and the limit analysis of large scale 3D structures such as arch dam is possible. The sub-iterative Newton algorithm (algorithm II) is developed to an algorithm with increment elastic stress transfer (algorithm III), and it is proved that the overload factor by algorithm III is not greater than the one by algorithm IV(the algorithm with increment elasto-plastic stress transfer). Then the algorithm III is proposed to calculate the limit load of arch dam.As a practical example, the FEM equivalent stresses and limit load of Lijiaxia arch dam is analyzed, and the strength safety of the dam is estimated.