INFLUENCE OF SSI ON THE MECHANICAL AND DYNAMIC PROPERTIES OF SEISMIC ISOLATION SYSTEMS IN SOFT SOILS

The use of seismic isolation systems in buildings founded on flexible soils requires an adequate study that evaluates the influence of the soil on the behaviour and performance of the isolation system under dynamic stresses such as earthquakes, due to the interaction of the flexible soil with the structure that produces significant changes in the seismic response, generated mainly by kinematic and inertial effects. Therefore, this article aims to evaluate the influence of soil-structure interaction (SSI) on the mechanical and dynamic properties of a five-story reinforced concrete building supported on an elastomeric low damping (LRD) type isolation system and another with a simple frictional pendulum system (FPS). The soil was modelled with springs and viscous dampers calculated using three SSI dynamic models: Barkan Model (BM), Sargsian Model (SM) and Shariya Model (ShM)). The seismic responses of interest evaluated in the isolation system were lateral forces, lateral displacements, lateral stiffness and vibration periods, with the purpose of determining the effective linear properties of both isolation systems. Seismic responses were determined by a nonlinear time history analysis (FNA) using seven pairs of ground motion acceleration records measured in flexible soils in Peru. Determining for the 8 proposed models, that the average maximum lateral displacements in the SSI models of both isolation systems presented lower values in the SM and ShM models, in addition to the influence of the SSI on the maximum lateral forces of the isolation systems. It is more notable in the SM and ShM models compared to the BM. Furthermore, it is shown that the implementation of SSI models increases the vibration period of the isolated structures mainly in the FPS system, which introduces additional damping effects due to energy dissipation at the soil-foundation interface, affecting the seismic response (axial forces, shear forces and moments). Finally, it is evident that the SSI has relevance in making decisions about the viability of isolating a structure founded on a flexible soil.