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Development of a Basic Method for the Preliminary Design of Seismically Isolated Structures

Salehi, Ahmad Ali | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50438 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Moghaddam, Hassan
  7. Abstract:
  8. For the preliminary design of isolated structures, it is necessary to select the appropriate damping ratios in each mode. The inherent modal damping in this type of structures is small. On the contrary, a significant value of damping is induced by dampers in isolator system into structural modes. The purpose of this study is to determine the Modal damping ratios in isolated structures. In this regard, shear structures of 2 to 10 floors with linear behavior in both superstructure and isolation level have been analyzed. The Structures have been modeled taking advantage of OpenSees. Samples are analyzed under sinusoidal loading applied to each floor. In order to achieve modal damping, an innovative method has been used in these structures. The sinusoidal loadings applied to floors in each model, are selected in such a way that it motivates only one mode of the structure. This process has been repeated for all modes in each model. By calculating the displacement response of the roof in each mode, the damping ratio of that mode is obtained by one of the damping calculation methods. MATLAB program has been used for damping calculation. The effects of different isolator parameters on the results are investigated. Besides, the achieving results are compared with the results of using approximate relationships available for modal damping estimation in isolated structures. Finally, the proposed method has been verified by comparing the results of modal analysis under a real earthquake record using calculated damping ratios and the results of analysis in SAP2000 program by modeling of damper in addition to the isolator instead of assigning modal damping ratios. The results indicate the high accuracy of this innovative method in calculating modal damping
  9. Keywords:
  10. Modal Analysis ; OpenSees Software ; Prelimanary Design ; Isolated Structures ; Modal Damping Ratios ; Damping Evaluation

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