Evaluation of Base Ground Stiffness on Statically Indeterminate Framed Building Structures

The aim of this paper is to investigate the influence of the modulus of subgrade reaction in statically indeterminate framed structures. In building's design the interaction between ground and foundation can be modelled variously: using springs instead of supports, modelling the wholesale soil as finite elements, etc.The most common situation in practice is that the interaction is modelled using the springs. Nevertheless,there is not just one approved method to calculate it, and engineers use different methods, proposed by various authors. In practice the settlements of foundations are usually calculated and compared with the limit value. However, in some cases the impact of settlements is not taken into account on the analysis of the structure. During the design process, the number of boreholes is always limited. Therefore, the real situation cannot be considered exactly. As a result, unforeseen settlements may cause the considerable redistribution of internal forces, leading to the cracking or even to the failure of the structure.In this research, different calculation methods of modulus of subgrade reaction are presented. Most of these methods are adopted for the base of foundations consisted of one soil layer. Therefore, an evaluation proposal of the modulus of subgrade reaction for multi-layered soils, using the reviewed methods, is suggested. Using those methods, the modulus of subgrade reaction of soils of 4 specific boreholes were calculated and compared. Furthermore, internal forces of two-storied framed building were calculated and compared in two different cases. In the first case the calculations are performed considering the settlements of the foundations. The settlements are calculated using 2 particular geological situations. In the second case all supports are assumed to be rigid