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Investigation on Performance Based Seismic Design of Concentrically Braced Frames

Zare Dastjerdian, Mehrdad | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40475 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Moghaddam, Hassan
  7. Abstract:
  8. Today, Stability review of existing structures is one of the most important problems that have underperformed in our country. Base of doing this important project is Instruction for Seismic Rehabilitation of Existing Buildings No.360. In these Criteria, Nonlinear Static Procedure (NSP) is the most popular analytical method. In this procedure, a building shall be modeled, analyzed, and evaluated as an assembly of elements and components. For modeling of components, in lieu of relationships derived from experiment or analysis, the generalized load-deformation with parameters a, b, c, shall be used for members of structure. These parameters were defined in Tables 5-6 and 5-7 for steel moment frames in issue 360. In first step of this project, Review of these modeling parameters in comparison with parameters obtained from tests was our objective. In next step, effect of these two procedures of defined parameters on behavior of some steel structures was investigated. These investigations, indicate that difference between effect of these two procedure was considerable (prestandard’s procedure in comparison with experimental procedure, was over estimated). This overestimation and uneconomical rehabilitation of structures result in many structures to give up this work and finally, according to this principal, loss of life increase in probable earthquake. In criteria of issue 360, for braces, the first controlling was compressive deformation of brace because of modeling parameters for this action, have large factor of safety. On the other hand, experimental investigations of others show that this parameter strongly depend on width/thickness and independent of slenderness of members but In this section, Author believed that prestandard was far from reality. In the next step of this project, the behavior of very slender braces such as bars in past experimental works was investigated. Noted that this prestandard Criterion seems any place for ductility of these members while experimental reports were contrary to this subject. At last section of this thesis, behavior of axially loaded braces with different sections under cyclic loading by finite element procedure was investigated. Results show that local buckling is the most important event in the behavior of these members. When braces loaded after some cycles, in the mid span of brace, local buckling was occurred. Before this event, the distribution of stress and strain in this section was uniform and after this, strains at some positions concentrated and axial strain was grown strongly. This phenomenon was called strain jumping. Later, braces section was cracked at this critical places and complete fracture at mid span was started.

  9. Keywords:
  10. Strain Localization ; Strain Jump ; Pushover Analysis ; Acceptance Criteria ; Deformation Usage Ratio ; Collapse Preventation

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