ANALYSIS OF R.C. FRAMED BUILDING CONSIDERING SOIL STRUCTURE INTERACTION

Abstract

Framed structures are commonly used in the construction of buildings and industrial structures. The conventional practice considers the isolated behaviour of structure during its analysis and design. In reality, however, supporting soil-foundation system alters the behaviour of superstructure and hence the need for considering the mutual interaction. A realistic analysis of a space framed structure founded on isolated footings leading to the settlement of footings is presented. The stiffness of soil is considered based on the conventional settlement relations. The phenomenon of overlapping of stresses and angular deflection of the footings are also considered. The frame is idealised as an assemblage of column and beam elements resting on spring supports. Iterative analysis is used to include the interaction of substructure and soil with the superstructure. The analysis yields stress resultants of the superstructure and substructure for design purpose. To simplify the approach attempt has'been made to replace original structure by a equivalent structure consisting of single level of grid of beams with columns resting on spring supports which includes all pertinent phenomena. A computer program based on direct-stiffness Matrix method incorporating the proposed method of analysis is developed. It is observed that differential settlements cause substantial amount of redistribution of forces in the superstructure. Foundation load and settlements obtained from equivalent structure are comparable with those obtained from original structure. Stiff foundation-beams help in reducing differential settlements and hence their effects on the superstructure