Role of Subgrade Reaction Modulus in Soil-Foundation-Structure Interaction in Concrete Buildings

One of the key issues in structural and geotechnical engineering is that most parts of buildings are usually analysed separately and then the outputs are used in foundation designs. In this process, some effects are neglected. In this study, the soil–structure interaction (SSI) in foundations of concrete buildings was evaluated using the direct finite element method (DFEM). 3D models were developed and used to analyse concrete buildings with different stories constructed on soft soil. Foundation settlement, deformation of foundation, soil pressure diagram, and weight of reinforcement in the foundation were considered as the main parameters. Deformation of the foundation was analysed using the finite element method considering the effect of combined loadings (combinations of dead load, live load, and earthquake load). It is shown that by changing values of subgrade reaction modulus (Ks) in foundation design, the effects of SSI on tall buildings can be considered automatically. The results also show that the soil–structure interaction can cause changes in the pattern of foundation settlement, foundation deformation, and the weight of reinforcement used in foundation design. Furthermore, dishing deformation in foundation appeared in terms of SSI effects. An equation is provided to simplify considering SSI effects in foundation design. This method is practical for civil (especially structural) engineers, and they can conveniently consider these effects in foundation design without using DFEM.

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