Study of water towers

Abstract

Water towers are prerequisite for providing the hydraulic head and partial storage to meet the fluctuating demands. Among different type of tanks used for water towers 'Intze' tank is an economical tank for reinforced concrete, because its ability to carry part of the water load by direct compressive forces. Stress analysis of 'Intze' tank is extremely complicated due to many degrees of redundancy. However, the elastic theory of thin shell with certain approximation may be used to analyze these tanks with sufficient accuracy. The principle stress system is obtained using membrane theory of shells. The deformations due to membrane forces are found to be incompatible at the junction where the different shells forming the tank meet and the continuity of the structure gives rise to edge restoring forces. The edge restoring forces and the perturbation or the membrane stress system due to edge forces are obtained by using compatibility equations and bending theory of shells. Along with the assumptions made in electric theory of thin shells, the following are included, 1 ) . The effect of edge restraining forces in the shell is predominant in the border zone, and diminishes away from the edge point. The restraining forces at one edge have only a small effect on stresses on deformation at the other edge, when the linear dimension is large compared to the thickness. Therefore it is assumed that the effect of restraining forces at one edge is independent to the end condition at the other edge. This assumption is satisfactory for the usual proportion of shells forming an 'Intze' tank. 2). Thomson's functions are approximated to the first term of the asymptotic expansion when the variable is greater than ten. The analysis of shell structures involves a two step procedure similar to the one used for statically indeterminate frames. In shell structures membrane analogy is used to obtain the principal stress system. Membranes theory assumes that a thin shell structure, because of its low flexural rigidity carries the loads by direct shearing forces in the plane of its surface. This assumption necessitates specific support conditions for the different families of shell and loading conditions.