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A Novel Discrete Model Proposal for Analysis of Soil-Structure Systems in Time Domain

Khodabakhshi, Parisa | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40089 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghannaad, Mohammad Ali
  7. Abstract:
  8. Soil-structure interaction may have a considerable effect on the response of the superstructure. One of the main steps in analyzing the soil-structure system is determining the soil impedances which vary with frequency. Although it is possible to analyze a dynamic system with complex frequency-dependent property matrices, this cannot be taken into account in most standard general-purpose softwares. In addition, the nonlinear behaviour of the structure can only be studied in time domain. Therefore, in the past two decades efforts have been made to replace the soil media with discrete models having a small number of degrees of freedom (DOFs) and a few springs, dashpots and masses with frequency-independent coefficients. The coefficients of elements are derived so that the dynamic stiffness of the model is consistent with that of soil media. In order to achieve higher degree of accuracy in these models, the number of the internal degrees of freedom is increased, but on the other hand, this will make the models less practical. In this thesis a novel discrete model for structures supported on rigid foundation embedded in homogeneous elastic halfspace is investigated, which is simpler than its counterparts in previous researches. For this purpose the surface discrete model that was proposed by wolf based on wave propagation in Cone Models is extended to embedded foundations. This will be done through introduction of a set of modification coefficients instead of adding DOFs to the model. These modification coefficients have been calculated for a practical range of nondimensional parameters, utilizing response-spectral-matching method. Finally, to make the results more convenient to use, simple equations are provided for the modification coefficients using nonlinear regression analysis. The accuracy of both frequency domain (transfer functions) and time domain (timehistory analyses) results of the proposed model, compared to the rigorous ones, is quite satisfying.

  9. Keywords:
  10. Soil-Structure Interaction ; Time History Analysis ; Embedded Foundation ; Soil Discrete Model ; Response Transfer Function

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