SOIL-STRUCTURE INTERACTION IN MULTI-STOREYED BUILDING FRAMES

Abstract

Soil—structure interaction is quite an important 'actor to consider in the analysis and design of variety of structures ranging from dams and retaining walls to multistoreyed building frames. This phenomenon is more pronounced in multistoreyed building frames especially, due to possibility of large unequal column loads, thus attracting more attention. The term soil—structure interaction is used for the mechanics of interaction between the foundation, soil and the superstructure. The pheno-menon in which the flexibility of foundation and the compressi-bility of soil mass alters the superstructure behaviour which in turn alters the foundation deformation pattern, is termed as soil—structure interaction. The dissertation work is aimed at developing a suitable approximate method to compute the member end forces due to soil—structure interaction in building frames so as to estimate the settlement pattern and the extent to which the superstructure behaviour is altered by the supporting soil mass so that frame and footings could be adequately and economically designed. The proposed method of analysis developed, determines stress—resultants in the structural members and the foundation settlement pattern, due to soil—structure interaction. These member stress resultants are then superimposed on to the stress resultants due to loads alone without considering, soil—structure interaction, to get final values of the stress resultants in the members. The method of analysis is based basically on the principles of displacement method. Firstly the original stru-cture is replaced by an equivalent structures, which is obta-ined by replacing the entire superstructure by a single level of grid of beams providing stiffness against different settle. men., equivalent to that of the super—structure of the original structure. Thus the equivalent structure consists of a total of two beam levels comprising of a foundation beam level and a super structure beam level at the level of the original first floor beams. For this equivalent structure, equilibrium equations and equations relating member stress resultants to joint displacements are written considering the compressibility of soil strata. The joint displacements obtained after solu-tion of these equations, are used to get stress resultants in the structural members. A computer program in Fortran IV incorporating the pro-posed method of analysis is developed. The results i.e. foundation settlement pattern and stress resultants in various structural members are compared with those using a plane frame program with fixity at base. The plane frame program has been modified to inOlude springs for considering soil—structure action. The results are compared with those obtained using the proposed method in which both the space action as well as soil—structure action have been considered. Suitable conclu-sions have been dfawn as a resu