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Investigation of Crack and Buckling Effects on Ultimate Capacity of Fixed Offshore Platforms with Dynamic Analysis Approach

Erfani, Mohammad Hadi | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53677 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Sayyadi, Hassan; Tabeshpoor, Mohammad Reza
  7. Abstract:
  8. Tubular sections and consequently tubular joints in construction of steel structures in the form of space frames is widely used in ground and marine structures, including offshore jacket platforms. The passage of part of the life of the existing offshore platforms has caused cracks in various parts of the joints of these structures due to various reasons, the most important of which is fatigue. In this thesis, by adopting numerous numerical studies and validations with some cited experimental papers, the principles governing the proper buckling behavior of tubular members focusing on the conventional geometries of Persian Gulf platforms as well as the behavior and local flexibility of tubular joints focusing on cracked K joints have been discussed. Axial load-bearing capacity of the braces comprises approximately 90 percent of the total lateral load-bearing capacity of an offshore jacket platform. Therefore, in the first step the effects of the existing fundamental parameters on the buckling behavior of tubular members have been investigated and the proper buckling behavior of these members based on experimental results has been achieved. The selected parameters include imperfection value, number of mesh elements on cross-section, and mesh size ratio (ratio of mesh size on length to the cross-section). These parameters have been studied versus various D/t and L/D ratios. At this part, the most important parameter in estimating the critical buckling load is the amount of ipperfection and the mesh ratio has been introduced as the most effective parameter on estimating the initial elastic stiffness and post-buckling strength. In the next step, the behavior of K-type tubular joints has been investigated and the LJF equations in both intact and cracked K joints have been presented. The presented equations have been developed based on the standard form of previously proposed equation in the literature and compared to the other forms in valid papers. Also, in order to study the effects of the findings of thesis on the overall behavior of the jacket structure, the geometries of the two existing platforms have been choosed include Resalat and South Pars phase 9-10 in the Persian Gulf. The proper estimation of buckling behavior of braces can affect the ductility of the structure up to 33% and the lateral bearing capacity of the structure up to 8%
  9. Keywords:
  10. Offshore Jacket Platform ; Bearing Capacity ; Buckling ; Crack ; Tubular Joint ; K Joints ; Tubular Members

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