Studies On Frame Structure With Mid-story Isolation Considering Soil-structure Interaction Effects

Mid-story isolation structure is a new type of isolating system based on the base isolation structure. In practical engineering application, because of the special terrain conditions and the need for the use of architectural features, it would require setting the isolation unit up in the middle layer, which is story isolating system. Story isolation system in the damping mechanism of shock damping system, vibration characteristics and design methods, and so on, are all different from the base-isolations. At Present, the research on isolation between layers is still in the primary stage, and there is no systematic theory and experimental research results. There is little research on mid-story isolation structure considering Soil-Structure Interaction. So, this paper aims at studying the properties of mid-story isolation system with SSI effect, observing SSI effects on mid-story isolation.This paper firstly analyzes the theory of the soil- mid-story isolation structure system and proposes a simplified method that combines the SR model of soil with three partial system of the structure. With this method, we can simplify a structure with mid-story isolation including soil-structure interaction into a five degree of freedom system. These degrees of freedom are superstructure, floor above isolation system, substructure, soil horizontal displacement and rotation angle of structure partial fixing. In order to simplify the solvent of the five degrees freedom system, this paper proposes an equivalent method that educes five degrees of freedom to three degrees by means of equaling soil stiffness to upper structure, then solves the modal characteristics. The results can provide theoretical support for parameter analysis of story isolation structure considering SSI effect.Within the help of SAP-2000, the parameter analysis can be carried out to study the change of structure period with the variation of structure and soil parameters. The change of natural period can be used to response the SSI effects. This paper selects the following related parameters: soil shear wave velocity, the isolation layer stiffness, stiffness ratio between superstructure and isolation, stiffness ratio between substructure and isolation, mass ratio between superstructure and substructure, and the mass of isolation layer.Using PERFORM-3D to do elastic-plastic analysis for four different structures which is structure without mid-story isolation and SSI, structure with mid-story isolation but without SSI, structure without mid-story isolation but with SSI, and structure with mid-story isolation and SSI. Compare the differences of seismic performance of structure considering SSI or not and structure with or without mid-story isolation. It can provide a basis for the design method of the mid-story isolation considering the effect of SSI in the future.