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Value-based Optimal Design of FPB and LRB Isolators for Short to Medium Rise Buildings

Rahgozar, Arash | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55557 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Esmail Pourestekanchi, Homayoon
  7. Abstract:
  8. Seismic base isolation is the most effective method of protecting and strengthening structures against seismic damage caused by large to small earthquakes and aftershocks. Providing damping and energy absorption of the seismic isolation at the structure's base level can significantly reduce the cost of repairing and strengthening the structure in addition to reducing seismic damage. However, besides these advantages, due to their high cost, seismic isolations in major infrastructure projects, hospitals, and crisis management centers should have economic and social justification. In this regard, a value-based seismic design approach can justify this important issue. In recent years of research regarding seismic isolations, despite the focus on the assessment of the state of the superstructure when exceeding the maximum displacement limit permitted by the regulations due to large earthquakes, the failure effects of the seismic isolator devices have been neglected. For this purpose, the contribution of this research is divided into two main sections: 1) proposing a more accurate equivalent two-degree-of-freedom system in predicting the global structure response, and 2) providing the necessary suggestions for updating the geometrical and mechanical property of seismic isolators that extreme failure modes did not consider. In the first part, the proposed two-degree-of-freedom system will greatly consider the effects of stiffness and strength deterioration, the effect of structure collapse under a large P-Delta, the uplift effect of vertical earthquakes on the reduction of the isolator capacity, and the moat wall impact phenomenon in order to properly predict the global collapse state of seismic isolator buildings. This system has been validated with a wide range of short to mid-range moment frame buildings. In the second part, the failure limit states of rubber-lead isolators (including compressive buckling and tensile rupture of rubber) and triple friction pendulum isolators (including extreme uplift and sliding exit from the end boundary) on their optimal properties were investigated for three special steel moment frame buildings of 4, 8 and 12 stories. The detailed modeling of these three buildings was done in OpenSees software and verified with the dynamic and non-linear specifications of the NIST report. The design objective is to optimize the isolation properties based on maximizing the value of the whole building. For this purpose, the initial construction cost and the lifetime damage cost of seismic isolation buildings were selected as valuable design parameters, the sum of which constitutes the total building cost. In other words, maximizing the total value of the building is defined as minimizing the total building cost in the lifetime. The structure response analysis is done with the help of the fifth generation of endurance time method named "kd" series excitation functions. The seismic consequences are predicted according to the FEMA P-58 loss analysis procedure. Finally, the efficiency of the results of the value-based approach is carefully compared to the code-based design approach. In rubber-lead isolators, on average, with a 2% increase in the optimal construction cost of the code-based method, the total value of the building can be increased by 8%. Also, in triple friction pendulum isolators, the total value of the building can be increased by 4.5%, with an average increase of 0.3% in the optimal construction cost of the code-based method.
  9. Keywords:
  10. Value Based Seismic Design ; Endurance Time Method ; Life Cycle Cost (LCC) ; Cost Analysis ; Vibration Isolators ; Steel Moment Frame Buildings ; Vertical Earthquake Component ; Moat Wall Impact ; Two Degrees of Freedom System

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