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Proposing an Appropriate Lateral Load Pattern for Push-over Analysis of Steel Moment Resisting Frame Structures with Mass Irregularity in Height

Ashrafi, Anahita | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 49703 (53)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Rahimzadeh Rofouei, Fayyaz
  7. Abstract:
  8. The irregularity in structures is divided into two categories of irregularity in vertical and irregularity in plan. The irregularity in vertical can be caused by ultra-change in dynamic properties of the structure such as mass, stiffness or strength. Research studies indicate that this irregularity leads to intensify the applied damages to structures in severe earthquakes. In general, nonlinear dynamic procedure (NDP) can provide more realistic results than nonlinear static procedures (NSPs). That is due to consideration of higher modes effects and the shifts in inertia load pattern as the structural system experiences nonlinear behavior. Nowadays, due to complexity of nonlinear dynamic analysis, utilizing nonlinear static analysis for determining forces and deformations in the event of earthquake is more common. This method is based on this procedure that a lateral load with predetermined pattern which is distributed in height of structure, is gradually applied to structure for reaching the node control displacement to target displacement. Nonlinear static analysis is divided into two categories of conventional and improved. In conventional approach, the effect of higher modes and stiffness change of structure on the load pattern are not considered but in improved approach with considering theses effects on lateral load pattern by various methods, the existing error in responses of higher stories of high-rising structures are decreased. In this study, the theory of the nonlinear dynamic and static analyses is discussed. Besides, a number of existing enhanced pushover procedures are elaborated in details. Next, the code of recommended load patterns and the aforementioned enhanced procedures are investigated using nonlinear dynamic time history analyses (NDTHA). For investigating the effect of load pattern on nonlinear responses of structure with mass irregularity in vertical, two models of 10 story moment resisting especial steel frame systems with mass irregularity in stories no.5 and no.8 are analyzed with nonlinear dynamic and static analyses. The displacement and drift story responses resulted by NDTHA and NSPs analyses are assessed. And finally, according to achieved results, appropriate lateral load patterns with considering the envelope two pushover analysis which consider effect of higher modes are represented. It is shown that the proposed method had a good agreement with NDTHA analysis and can properly predict the nonlinear response of structure
  9. Keywords:
  10. Nonlinear Static Analysis ; Lateral Load Pattern ; Nonlinear Dynamic Analysis ; Vertical Irregularity ; Mass Irregularity ; Steel Moment Resistant Frame ; Seismic Excitation

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