ANALYSIS OF CONICAL SHELL FOUNDATION FOR WATER TOWER

Abstract

A conical shell foundation having a slab on top under vertical axisymmetric load has been analysed. Firstly, conventional analysis has been presented for which membrane theory has been developed, which takes into account the normal and tangential pressure at contact. As the base pressure distribution is not known, so assuming the base pressure uniform at base level,the membrane analysis and then continuity analysis for bending stresses has been carried out. Results are also obtained by using linear solid axisymmetric finite element analysis. The contact soil pressure distribution, soil pressure at base, the distribution of soil pressure in the confined soil mass, stress resultants, bending moments, hoop moments and the settlement-characteristics are presented for following variations i) Effect of variation of modular ratio Bc/Es of concrete and soil by taking Ec /Es as 100, 500 and 1000 and half vertix angle a = 450 . ii) Effect of variation of half vertex angle a by taking a as 45o and 60o and Bc /7.,' as 1000. iii) By providing two types of toes at the shell edge a) Rectangular Toe b) Inclined toe, perpendicular to the generator axis throughout the shell while keeping modular ratio Ec/Es = 1000 and half vertex angle .a as 45°. Attempt has also been made to provide design charts for different soil pressures and stress resultants and useful conclusions are drawn regarding the general behaviour.