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Effect of Soil-Structure Interaction on Floor Acceleration Response of Buildings during Earthquakes

Tavakoli, Maryam | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43973 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghannad, Mohammad Ali
  7. Abstract:
  8. Observed performance of nonstructural components and building contents during recent earthquakes demonstrated their significance to control economic seismic losses and downtime. Since a large portion of nonstructural equipments installed in buildings are acceleration sensitive devices, reasonable estimation of the acceleration they undergo during an earthquake has an important role in rational design of secondary systems and subsequently in reducing the earthquake damages. Although a comprehensive amount of research studies have been conducted to date to approximate the floor acceleration demands of a multistory building subjected to the earthquake ground motion, in most work, the soil beneath the structure is assumed to be rigid. While, in fact, the dynamic properties of structures are mainly influenced by flexibility of soil under them due to Soil-Structure Interaction (SSI). Hence, the floor acceleration responses of a building as a part of the soil-structure system would be almost different from that of the fixed-base state.
    The main objective of this study is to illustrate the SSI effects on the intensity and spatial distribution of peak floor accelerations in buildings responding elastically to base excitations. The soil-structure system has been modeled using the substructure method. Dynamic characteristics of the superstructure are approximated by using a shear-flexural model of multistory buildings. Soil beneath the structure is considered as a homogenous half-space and is simulated by springs and dashpots on the concept of Cone Models. Modal properties of the soil-structure system are evaluated through the non-classical modal analysis. The total acceleration response history of system subjected to earthquake is then obtained by superposition of the modal responses of all modes of vibration.
    In this work, a parametric study of acceleration responses of soil-structure systems is performed for a wide range of non-dimensional parameters which completely define the problem. It is shown that SSI has a considerable effect on the intensity and variation of peak floor acceleration along the height of building. When the SSI effect is significant, amplification of floor acceleration demands at top stories decrease considerably compared to that of the assumed fixed-base model. Lateral stiffness ratio is another parameter may also influence the acceleration response of system but with lesser effect than soil parameters.
    Finally, a simplified method is introduced to improve the established methods for quick estimation of floor accelerations. The method can be used to estimate floor acceleration demands in soil-structure systems for a given ground motion record
  9. Keywords:
  10. Nonclassical Modal Analysis ; Simplified Method ; Shear-Type and Flexural-Type Deformation ; Soil-Structure Interaction ; Acceleration Response

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