Assessments of performance and reliability of template-type offshore platforms under extreme hurricane conditions

As the fleet of aging offshore platforms is becoming larger and larger, the need to access and requalify them is becoming more and more demanding. Detailed structure analysis turns out to be expensive and impractical to fully address this demand. The call for a simpler and more efficient analysis process led to a seven-year joint industry-government sponsored research project at University of California at Berkeley. The research described in this dissertation is a part of the long-term effort to simplify the process of structural reliability analysis of platforms without compromising accuracy. The focus of the research is the assessment of performance and reliability characteristics of conventional, steel, pile supported template type platforms in extreme condition hurricanes. This dissertation documents a comprehensive study and evaluation of the important factors that control the performance and reliability of offshore platforms and summarizes the formulation, development, verification and completion of a versatile computer analysis program—TOPCAT (Template Offshore Platform Capacity Assessment Tools).; Different assessment and requalification analysis methods are applied in this dissertation to verify the validity of the simplified structural reliability algorithms used in TOPCAT. Analysis formulas were developed to include shallow water wave kinematics, effects of spatially distributed wave loads, diagonal wave loading, reliability sensitivity analysis, long-term reliability analysis and platform deck element analysis. The analysis model in TOPCAT computer program is a 3-dimensional one that is capable of analyzing 3-D distributed loads and global torsion. During the development of this analysis tool, a wide-range of factors influencing performance and reliability are addressed. These include: effects of Type I (natural) and Type II (analytical model) uncertainties in demands and capacities; effects of correlation; effects of truncations in loadings (deformable sea floor effects on wave characteristics); effects of foundation elements and systems; effects of structure elements and systems (deck, jacket, joints); effects of forces modeling (wave in deck forces); and effects of structure modeling (2-D and 3-D). Case studies are conducted to verify the analysis processes developed during this research. This research is of interest to offshore engineering and regulatory communities, including platform owner/operators, and engineering consulting companies.