The Weakness of Using Springs for Representing Soil

This paper presents the effect of the soil structure interaction on the modulus of subgrade reaction. Many of structural designers represent the footings as hinged support in the structural models, while the other de-signers represent the footings as a group of springs with spring coefficient K (kN/m). Designers assumed this modulus by different equations that are not considering the soil structure interaction. This paper showed that, the soil structure interaction has a significant effect on the modulus of subgrade reaction. k_s is not uniformly distributed under the footings. Using of soil structure interaction in the calculation of the normal forces in columns is resulting a relatively change. Plane two-bay frames and two-bay by two-bay frames were studied using geotechnical and structural 2D and 3D finite element programs, respectively. It is investigated for the plane frames that, the normal force in the inner wall decreased and it is increased for the outer walls. For the three dimensional frames, the inner column’s normal force is decreased and the edge column’s normal force is increased with the same normal force in the corner walls. For the complex structural systems, the distribution cannot be estimated, so the use of geotechnical finite element programs that can consider the soil, foundation, and superstructure effect is highly recommended for the practical and researcher engineers.