EFFECT OF SOIL STRUCTURE INTERACTION ON ANALYSIS OF SUPERSTRUCTURE

Abstract

Superstructures are generally analysed considering their bases as either totally fixed or hinged, completely neglecting the underneath foundation and soil. Due to the difference in the rigidities of foundation, soil and superstructure the foundation undergoes some amount of deformation. This deformation shows it effect on the superstructure. Therefore an interactive analysis is necessary for the exact and more accurate response of the superstructure. A G+3 storey building frame with two bay resting on pile foundations is considered to demonstrate the effect of Soil Structure Interaction (SSI). The pile foundations are embedded in clayey soil. A finite element code is developed in FORTRAN 90 assuming complete 3D behaviour of the superstructure as well as the substructure. An uncoupled analysis is employed for the analysis in which the superstructure and substructure are considered as two different entities and are analysed separately which reduces the computational effort and saves time and memory. The results obtained from SSl analysis are compared with the one obtained from the fixed base condition. A parametric study is conducted by varying the LID ratio of piles, diameter of piles, Modulus of elasticity of soil. The effect of change in these parameters is observed by analysing the top displacements of the building frame as well as bending moments in both beams and columns. It is observed that these values have increased by a considerable factor when SSI is taken into - consideration for the analysis