Analysis of raft foundation using Winkler’s linear spring in SAP 2000 by considering varaying soil subgrade modulus

Abstract

Most of the civil engineering structures are designed by assuming rigid foundation without considering the
flexibility of soil. Ignorance of considering actual stiffness of foundation may misleading estimation of forces, the
bending moments, the settlements etc. It is therefore necessary to carry out the analysis considering the soil, the
foundation and the superstructure, which form a single compatible unit. The various methods available for the design of
raft foundation, in the conventional method the base of raft foundation consider rigid in order to control the total and
diffential settlement, which result in uneconomical design. The real behavior of raft foundation can be obtained by
considering the soil flexibility. Among the various option available for analysis of raft foundation an attempt has been
made to study the behavior of raft foundation resting on Winkler’s linear spring. A model is prepared and study is
carried out with different raft size configuration with varying soil subgrade modulus.
The Building and foundation analysis has been done using professional software (ETAB and SAP). Different multi-storey
building such as 15 & 20 Storey building and their foundation (i.e. raft size 16 x 16m, 20 x 20 m, 24 x 24 m) are analyzed
by considering various soil subgrade modulus(Ks=4000 kN/m3
, 5000 kN/m3
and 6000 kN/m3
). The comparison of these
models has also been carried out in the study. The parameters varied for the study are: (I) modulus of subgrade reaction
of the soil, (II) number of storey and (III) size of raft. A comparison of Raft size and settlements, Soil subgrade modulus
and settlement, no of storey and settlement is done. Also comparison of Raft size and bending moments, soil subgrade
modulus and bending moment, no of storey and bending moment is done.