STUDY OF ANNULAR - -RAFT FOUNDATIONS BY FINITE ELEMENT METHOD

Abstract

The finite element analysis of several annular raft foundations has been carried out for medium and large size capacity tanks. The problem has been studied as a complete soil structure interaction problem-by assuming linear elastic behaviour of soil. Studies have been carried out for wide variation of elastic mo dulii of soil by varying the ratio Ec/FS as 40, 100, 200 and 400. Detailed studies have been carried out for annular rafts of tanks for 250 KL , 1500 KL and 2200 XL capacities. Studies have been carried out for determining the soil pressure distribution for various cases. Effect of varia-tion of raft thicknesses and effects of variation in lean concrete thicknesses have been studied for various widths of the raft foundations. In case of shaft the effect of superstructure stiffness has been studied by considering the raft with shaft and without shaft. The significant conclusions have been verified by applying statical checks and compared with conventional design procedures. In case of 2200 EL tank, an innovative design of annular composite raft foundation has been adopted. In this raft, a weaker concrete has been used in the middle portion near the neutral plane of the raft. Detailed stress analysis of such a system has also been carried out along with it `s eventual effect on economy.