2-D STRESS ANALYSIS OF KOYNA DAM BY FINETE ELEMENT METHOD

Abstract

Numerical methods allied to powerful digital computers give to-day the possibility of solving almost all well defined physical problems with desirable accuracy. The finite element process of discretizing and approximating continuous problems has proved itself to be one of the most general and useful procedures. In the design of gravity dam‟s gravity method of analysis is widely used all over the world the gravity method of analysis of dams is based on many simplifying assumptions and cannot take into actual site conditions. Finite element method used in analysis of gravity dam because it gives more accurate results than conventional methods. In my thesis two dimensional finite element analyses is carried out because 1) in three dimensional analysis some loads are distributed to dam abutments so stresses are less compared to two dimensional analysis. 2) three- dimensional analysis is costlier, tedious than two dimensional analyses.

FEM requires the domain of interest be subdivided into a mesh of discrete elements or sub-domains. The accuracy and the expense of the calculations are strongly affected by the “goodness” of the underlying mesh.

Ideal mesh is characterized by finer elements at curved boundaries and also where stress concentration is high. To develop finer elements and data preparation for smaller elements by manually is very tedious, time consuming and error prone. Automatic mesh generation is used for creation of a well- conditioned mesh in two dimensions with a minimum of user interaction using isoperimetric quadrilateral elements.

Present work deals with the finite element method and it has been studied for both plain stress and plain strain condition. The convergence of the problem is checked with three different mesh types of 36 elements, 73 elements and 160 elements for all the cases stresses are worked out. The graph has been plotted for the normal and shear stresses. According to IS: 6512-1984 the analysis is carried for load combinations A and B. for all load combinations according to saint venant‟s principle foundation interaction of dam is included in stress analysis. Analysis is done for including and excluding the foundation interaction. It is observed that the stresses including foundation interaction are more compared with the stresses when foundation interaction not considered. A programme in „C‟ for analysis and BASIC programme for the mesh generation is used in the present thesis.