KINEMATIC SOIL-STRUCTURE INTERACTION EFFECTS ON INELASTIC SYSTEMS WITH EMBEDDED FOUNDATION

The soil-structure interaction can affect the elastic and inelastic seismic response of buildings. In other words, the fixed-base assumption is not always correct to determine the dynamic response of structures. The soil-foundation-structure interaction initially changes the input motion applied to the system, which is known as kinematic interaction (KI). Its second effect is the change in the dynamic properties of the soil-structure system (longer natural period and usually higher damping). The radiation of energy of the propagating waves away from the structure in the semi-infinite soil media, generally increase the soil-structure damping. This effect is called inertial interaction (II) (Wolf, 1985). In this paper, the effects of kinematic and inertial interaction on ductility demand of SDOF structures with embedded foundation are assessed. The SSI effect is simulated by beam on Winkler foundation approach. A comprehensive parametric study is also carried out and the effects of various parameters including design ductility, fundamental period of vibration, level of soil flexibility, embedment ratio and aspect ratio on the ductility demands are evaluated. The SDOF structure is characterized by its fundamental period Tfix, design ductility ratio of the fixed-base model μfix and damping ratio ξs. The effective mass and the effective height of the superstructure are denoted by m and h, respectively. The soil beneath the foundation is replaced by a set of spring-damper elements (Figure 1). The Qzsimple2 material is used in the OpenSees platform to define the nonlinear inelastic behavior of the base slab vertical springs (Raychowdhury, 2008). Figure 1 shows the horizontal springs and dashpots representing sidewall–soil stiffness, kside, and damping, cside, respectively.

Keywords:

Kinematic interaction , Foundation input motion , Embedded foundation , Soil-structure interaction