THREE DIMENSIONAL STRESS ANALYSIS OF CONCRETE GRAVITY DAMS

Abstract

In the conventional method of design of gravity dams, the dams are treated as two dimensional structures. This assumption is justified if the dam is located in a wide valley and the transverse joints are neither grouted nor keyed. However in narrow valleys, transverse joints in the dam are invariably provided with shear - keys and grouted so that the loads are withstood by the dam as a monolithic structure. The external load is shared by the vertical cantilever and horizontal beams. The load is, therefore 9 transferred partly to the foundation and partly to the abutments. In such cases economy can be achieved by adopting a smaller section of the dam if the design is based on three dimensional studies. The load transfer to abutments will depend upon the valley width and shape and will be negligible in very wide valleys. It is, therefore, imperative to know the limiting valley width beyond which the dam essentially acts as a two dimensional structure and grouting of trans-verse joints can be dispensed with. Very little work has been reported on the three dimensional analysis of gravity dams. However some work on earth and rockfi Ll dams using throe dimensional finite element analysis has been reported and a brief review of the same is presented. -iv- In this dissertation three dimensional stress analysis of a gravity dam located in a symmetrical valley has been carried out by varying the valley width and the results compared with the corresponding results of a two dimensional finite element analysis. The effect of variation of the valley width on the stresses and displacements in the dam has been investigated. The effect of the foundation elasticity on the three dimen-sional behaviour of dam has also been studied. It is concluded that for dams located in valleys with valley width to height ratio greater than 6 the dam essentially behaves as a two dimensional structure and that the foundation elasticity considerably affects the magnitude and distribution of stresses and strains in the dam..