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A Study on Importance of Overstrength Factor in Inelastic Behavior of Soil-Structure Systems

Bakhtiari, Ali | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49850 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ghannad, Mohammad Ali
  7. Abstract:
  8. Recent studies on inelastic behavior of soil-structure systems indicate that seismic design codes provisions, which use the same response modification factor for fixed base structures and soil-structure systems, are not appropriate and could lead to an increase in ductility demand of structures (as a part of soil-structure system). As a result, to reduce design base shear and design forces with regards to collaboration of soil-structure interaction could be in non-conservative manner. In all of these studies, the ductility component of the response modification factor (i.e. Rµ ) has been the major concern and the overstrength component has been ignored. However, the existence of overstrength affects the nonlinearity of the structure. The main objective of this research is to study the nonlinear behavior of soil-structure systems regarding the overstrength of the structure. The overstrength factor is dependent to natural period of the structure, attributed seismic design category and the structure’s lateral bearing system. Therefore, the amount of nonlinearity of two structures with the same response modification factor, would not be the same. Also, the dominancy of SSI in inelastic behavior of structure is dependent to the amount of nonlinearity in the structure. Hence, the dominancy of SSI in inelastic behavior of the structure is dependent to the value of the structure’s overstrength factor. In this research, at first, the major past studies on inelastic behavior of soil-structure systems, and also studies on structural overstrength are reviewed. Then, 15 reinforced concrete special moment frame structural models in various heights, and with different attributed seismic design categories are designed, and then in order to calculate their overstrength factor by means of pushover analysis, they are inelastically modeled in OpenSees. The results, show the dependency of overstrength factor values to the natural period of the structure and seismic design category. Then, by using the calculated overstrength factors for the structural models of each studied seismic design category, a function called “ Overstrength-Period” is attributed to each SDC. These functions are obtained by means of fitting the best possible power function to the couples of overstrength-period. By using these functions, for a specified seismic design category, one can predict the overstength factor of a structure knowing its natural period. Then, these functions are introduced as inputs to the program which is written in Matlab for modeling and analyzing the inelastic behavior of soil-structure systems. In this program, for modeling the soil-structure system, the structure is substituted with a single degree of freedom elastoplastic model and for modeling the soil, cone models are utilized
  9. Keywords:
  10. Pushover Analysis ; Base Shear ; Inelastic Behavior ; Response Modification Factor (R) ; Ductility ; Soil-Structure Interaction ; Natural Structure Period ; Overstrength Column Factor

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