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Upgrading the Existing Methods for Seismic Evaluation of Soil-Structure Systems with Embedded Foundation

Jahankhah, Hossein | 2010

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 41151 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghannad, Mohammad Ali
  7. Abstract:
  8. Base flexibility of structures, cause changes in seismic input motions to the structure, and hence, result in variations in structural seismic responses. This phenomenon is commonly referred to as soil-structure interaction (SSI). The effect of base flexibility on seismic responses is usually investigated from two main aspects: 1) Kinematic interaction (KI) , 2) Inertial Interaction (II). KI effects are induced, first, because of the stiffness contrast between the foundation and the flexible base, and second, because of phase difference of the receiving waves in the contact boundary between the foundation and the flexible base. These effects may results in variations in frequency content of and number of excitation components. II effects are in fact, the effect of SSI on response of structures after KI effects. These effects are usually included through modifications to dynamic parameters of the system. The above SSI aspects are reflected in the seismic regulations for design and evaluations of structures. In the case of KI effects, spectral modifications coefficient are provided with which the free field seismic response spectra are modified. To include II effects in seismic regulations, in the case of time history analysis, typical soil models are presented; while in the case of spectral analysis, equations for calculation of equivalent dynamic parameters are provided. An important point, in all above mentioned regulations, is that they are primarily derived for the case of surface foundations and then, approximately extended to the case of embedded foundations. In such stream, some point are missed or at least not properly included. For instance, for embedded foundation, KI induced rocking motion is ignored. Also simultaneous effects of structural nonlinearity and base flexibility on effective dynamic parameters are not considered properly. For soil models, frequency dependency of soil impedances is ignored or roughly considered. In this research, first, seismic demands of soil-structure systems with embedded foundations are investigated. Then, efficient procedures for seismic demand estimation are presented that hold enough accuracy and proper simplicity. In this regard for both KI and II effects existing methods are investigated and some of their shortcomings are discussed. Then efficient alternative methods are suggested
  9. Keywords:
  10. Soil-Structure Interaction ; Seismic Assessment ; Embedded Foundation ; Equivalent Dynamic Properties ; Rocking Motion

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