Effects of soil and tie beam on the dynamic behavior of a 4-story structure with spread footing system

All loads acting on structural systems must be safely transferred to the soil medium, and after the soil properties are determined, an appropriate foundation system is selected by considering the loads and the cross-sectional properties of the structural elements. The main objective of this study is to evaluate the effects of soil type, foundation tie beam, and earthquake frequency content on the seismic behavior of a four-story building with a spread footing system, in terms of displacement, acceleration, and stress responses. For this purpose, dynamic analyses based on the finite element method were carried out by considering two structural systems (with and without tie beams), five soil types, and three ground motions. It was determined that the earthquake frequency content which can cause changes in the strength and deformation characteristics of soils and the support conditions of the structure should be considered as design criteria. It was also found that the maximum responses were obtained respectively under earthquakes with medium, low, and high frequency content, and that for structures with low periods, earthquakes with medium and high frequency content may be more critical. Furthermore, it was observed that the use of a tie beam did not cause a significant change in the responses under relatively stiff soil (S1, S2, and S3) conditions; however, under soft soil (S4) conditions, the use of a tie beam reduced the maximum displacements and stresses during earthquakes with low and medium frequency content, while it increased them during earthquakes with high frequency content.