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Application of Endurance Time Method on Optimal Performance Based Design of Steel Structures

Charkhtab Basim, Mohammad | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40192 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Esmaeil Pourestekanchi, Homayoon
  7. Abstract:
  8. In recent decades, most of the codes have placed a high value on Performance Based Design of structures; however, these methods are computationally complex and time-consuming, and caused researchers to seek new and efficient methods to investigate performance of structures under different intensities of seismic loading. This issue is much more obvious when optimum design of structures, which requires repetitive analysis, is investigated. In the present research, using Endurance Time analysis, we are trying to provide better insights into the dynamic behavior of structures in continuous performance levels. Then, as a first step, we will use the verified method to find the optimum outline of viscous dampers in steel frames, and in the second step, the optimum cross-section of moment resisting steel frames will be investigated. Endurance Time Method consists of excitation of a structure through increasing accelerograms which their different durance indicate various intensities of earthquakes in different hazard levels. Endurance Time Method significantly decreases amount of computation in each step; consequently, various optimization methods can be employed to define design parameters. According to this, various inelastic moment-resisting steel frames, which possess some flaws in primary designing phase, are modeled using OpenSees. Furthermore, genetic algorithm is employed to define the optimum outline of dampers throughout the structure in a way that the structure reaches the allowable performance at the lowest cost. In addition, the performance of the structure under seismic excitation in different performance levels is evaluated based on interstory drift ratios before and after rehabilitation. In all cases, the improved structure has an acceptable performance during seismic loading, and Endurance Time accelerogram leads to an almost proper prediction of structure behavior at various earthquake records. The mentioned method is developed to identify the optimum cross-section of moment resisting steel frames using uniform deformations theorem. In this method, by using a numerical method, structural materials are gradually moving from the stronger parts of structure to the weaker parts in order to reach the optimum distribution of resisting elements. In this structure, deformations reach their acceptable values in all elements and the structure is lighter besides the least structural damages occur under seismic excitation. In this research, ASCE-41 is used as the performance base design criterion.

  9. Keywords:
  10. Optimization ; Genetic Algorithm ; Performance Based Design ; Viscous Damper ; Uniform Deformation Theory ; Endurance Time Method

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