This is the first of four companion papers that present a comprehensive assessment of the effect of sea floor subsidence on the Valhall complex of platforms. The study has included an estimate of the increase in platform failure probability as a function of increased subsidence. Subsidence raises the effective mean still water level and increases the potential for inundation of the deck for extreme storm conditions. Deck wave slam forces generate significantly greater platform loading and lead to: (a) higher levels of structural inelastic response and increased risk of structural failure as well as (b) water reaching the cellar deck, and hence affecting operators as well as equipment. The paper focuses on addressing the first of these two issues. A structural assessment study was performed to address the significance of present and future levels of subsidence on the safety of three North Sea platforms. The study included a systematic assessment procedure that addressed each of the factors that impacted structural integrity issues and reliability concerns. Such factors included: ultimate strength analysis methodologies, tubular joint formulations, group pile effects, and soil-structure interaction, which are described in this paper, as well as deck impact force formulations (Pawsey et al., 1998, “Characterization of Environmental Loads on Subsiding Offshore Platforms,” 17th International Conference on Offshore Mechanics and Arctic Engineering, Lisbon, Portugal, July) component and system reliability modeling (Jha et al., 2000, “Assessment of Offshore Platforms Under Subsidence—Part II: Analysis and Results,” ASME J. Offshore Mech. Arct. Eng., 122, pp. 267–273), and acceptance criteria (Stahl et al., 1998, “Acceptance Criteria for Offshore Platforms,” 17th International Conference on Offshore Mechanics and Arctic Engineering, Lisbon, Portugal, July). This paper presents the assessment procedure, as well as the modeling approach. The paper also discusses the consequence classification of the three platforms and state-of-the-art soil mechanics techniques that lead to a significant increase in the tensile capacity of the foundation. [S0892-7219(00)00204-1]
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November 2000
Technical Papers
Assessment of Offshore Platforms Under Subsidence—Part I: Approach
Joseph M. Gebara,
Joseph M. Gebara
Aker Engineering Inc., Houston, TX 77079
11
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Dan Dolan,
Dan Dolan
Bechtel Offshore, San Fransisco, CA 94142
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Stuart Pawsey,
Stuart Pawsey
Digital Structures, Berkeley, CA 94704
22
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Philippe Jeanjean,
Philippe Jeanjean
BP Amoco Corporation, Houston, TX 77079
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Knut Dahl-Stamnes
Knut Dahl-Stamnes
BP Amoco Norge AS, Stavanger, Norway
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Joseph M. Gebara
11
Aker Engineering Inc., Houston, TX 77079
Dan Dolan
Bechtel Offshore, San Fransisco, CA 94142
Stuart Pawsey
22
Digital Structures, Berkeley, CA 94704
Philippe Jeanjean
BP Amoco Corporation, Houston, TX 77079
Knut Dahl-Stamnes
BP Amoco Norge AS, Stavanger, Norway
Contributed by the OMAE Division and presented at the 17th International Symposium and Exhibit on Offshore Mechanics and Arctic Engineering, Lisbon, Portugal, July 5–9, 1998, of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. Manuscript received by the OMAE Division, October 1998; revised manuscript received April 21, 2000. Associate Technical Editor: C. Guedes Soares.
J. Offshore Mech. Arct. Eng. Nov 2000, 122(4): 260-266 (7 pages)
Published Online: April 21, 2000
Article history
Received:
October 1, 1998
Revised:
April 21, 2000
Citation
Gebara, J. M., Dolan, D., Pawsey, S., Jeanjean, P., and Dahl-Stamnes, K. (April 21, 2000). "Assessment of Offshore Platforms Under Subsidence—Part I: Approach ." ASME. J. Offshore Mech. Arct. Eng. November 2000; 122(4): 260–266. https://doi.org/10.1115/1.1313530
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