EFFECTS OF DIFFERENTIAL SETTLEMENT IN R.C. FRAMED BUILDINGS

Abstract

Framed R.C. structures whether it is a residential building, an industrial building or a warehouse, are common in today's construction. Whether or not total settlement is • objectionable there can be no doubt about differential settlement. Stresses developed in the structure are a function not only of imposed loads, but also of support movements in the case of rigid systems. Support movements are dependent on 'characteristics of soil below it and rigidity of the structure. Interplay between foundation, soil and structure on redistribution of forces developed due to support movements is called soil-structure interaction Problem. Even though the effects of interaction are well known and are known to be significant in certain cases, they are only rarely considered in conventional practice of routine design.The reason for this is that application of available methods is too complex to encourage the practicing engineer to use them in routine design practice. In the present dissertation a simplified but realistic analysis of a space framed structure founded on isolated footings is presented which takes into account interplay between soil, footings and superstructure. The stiffness of soil is considered in the form of elastic springs and calculated from the conventional settlement and rotation relations. The method of analysis is based on iterative displacement approach. Stiffness matrix method is used for the analysis by idealizing the structure as an assemblage of beams and columns resting over spring supports. Differential settlement and its consequences on structure are studied and it is observed that differential settlement causes substantial amount of redistribution of forces in the super-structure. Adjacent columns considerably influence the settlement pattern of a particular footing. Differential settlement and its consequences can be reduced substantially by providing more uniform foundation pressure and also by providing stiff foundation beams.