Cyclic Stiffness Degradation in Nonlinear Jackup Dynamics
- Authors
- Edward T.R. Dean (Soil Models Limited) | Rich Metters (Geotechnical Engineering and Marine Surveys Limited)
- DOI
- https://doi.org/10.2118/132170-PA
- Document ID
- SPE-132170-PA
- Publisher
- Society of Petroleum Engineers
- Source
- SPE Projects, Facilities & Construction
- Volume
- 5
- Issue
- 02
- Publication Date
- June 2010
- Document Type
- Journal Paper
- Pages
- 89 - 96
- Language
- English
- ISSN
- 1942-2431
- Copyright
- 2010. Society of Petroleum Engineers
- Disciplines
- 2.4.3 Sand/Solids Control, 4.5 Offshore Facilities and Subsea Systems, 5.1.5 Geologic Modeling, 4.3.4 Scale, 1.6 Drilling Operations
- Downloads
- 1 in the last 30 days
- 156 since 2007
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| SPE Non-Member Price: | USD 35.00 |
Introduction
The load-deflection response of the elevated hull of an installed jackup, subject to environmental loading, and the stresses at the leg/hull connections, depends on the stiffness of the spudcan foundations and thus on the moduli of the soils supporting them (Osborne et al. 1991; Dean et al. 1992; Temperton et al. 1997; Martin and Houlsby 1999; Nelson et al. 2000; Cassidy et al. 2002; Dier et al. 2004). Typically, soil moduli decrease with increasing cyclic-strain amplitude (Atkinson 2000). Soil stiffness can also change as a result of cyclic-strain history and because of buildup of excess pore-water pressures, both because of a sequence of storms, and during a design storm (Hsu 1998).
SNAME (2002) uses the concept of a yield envelope to determine combinations of vertical and horizontal loads and moments on a spudcan that cause significant elastoplastic responses. The envelope is used as if it were a failure envelope in the Step 2 bearing capacity check, which includes an option to allow for rotational foundation stiffness. If the jackup fails Step 2, it can still be accepted if it passes a Step 3 displacement check, which can include allowance for hardening. Sophisticated models of this type include Schotman (1989), Dean et al. (1997a; 1997b), van Langen et al. (1997), Cassidy et al. (2004), Bienen et al. (2006), and others.
This paper explores the guidelines using a simplified jackup response model. Results are found to be potentially conservative if stiffness degradation is ignored. Stiffness degradation is shown to produce significant nonlinearity in dynamic responses. An implication appears to be that observations in mild seastates do not extrapolate linearly to more severe seastates.
| File Size | 359 KB | Number of Pages | 8 |
References
Atkinson, J.H. 2000. Non-linear soil stiffness in routine design.Géotechnique 50 (5): 487-508.
Bienen, B., Byrne, B.W., Houlsby, G.T., and Cassidy, M.J. 2006.Investigating six-degree-of-freedom loading of shallow foundations on sand.Géotechnique 56 (6): 367-379.
Cassidy, M.J., Houlsby, G.T., Hoyle, M., and Marcom, M.R. 2002. Determiningappropriate stiffness levels for spudcan foundations using jack-up caserecords. Proc., 21st International Conference on Offshore Mechanics andArctic Engineering (OMAE), Oslo, Norway, 23-28 June.
Cassidy, M.J., Martin, C.M., and Houlsby, G.T. 2004. Development andapplication of force resultant models describing jack-up foundation behaviour.Marine Structures 17 (3-4): 165-193.
Dean, E.T.R., Hsu, Y.S., James, R.G., Schofield, A.N., Tan, F.S.C., andWong, P.C. 1992. The bearing capacity of conical footings on sand in relationto the behaviour of spud footings of jackups. In Predictive Soil Mechanics:Proceedings of the Wroth Memorial Symposium, ed. B.G.S. Parry and R.H.G.Parry, 140-161. London: Thomas Telford.
Dean, E.T.R., James, R.G., Schofield, A.N., and Tsukamoto, Y. 1997a.Theoretical modeling of spudcan behaviour under combined load. Journal ofthe Japanese Geotechnical Society: Soils and Foundations 37(2): 1-15.
Dean, E.T.R., James, R.G., Schofield, A.N., and Tsukamoto, Y. 1997b.Numerical modeling of three-leg jackup behaviour subject to horizontal load.Journal of the Japanese Geotechnical Society: Soils and Foundations 37 (2): 17-26.
Dier, A., Carroll, B., and Abolfathi, S. 2004. RR289--Guidelines forjack-up rigs with particular reference to foundation integrity. London: HSEBooks.
Duffing, G. 1918. Errzwuhgene Schwingunge bei vemderlicher Eigenfrequenzund ihre technische Beteutung. Braunschweig, Germany: Vieweg.
Foundation Fixity of Jack-Up Units: A Joint Industry Study. 1987. Report No.L13829/NDA/MJR, Noble Denton & Associates Ltd., London (10 March 1987).
Hsu, Y.S. 1998. Excess pore pressures under cyclically loaded model jack-upfoundations. PhD dissertation, Cambridge University, Cambridge, UK.
Kramer, S.L. 1996. Geotechnical Earthquake Engineering. Upper SaddleRiver, New Jersey: Prentice Hall.
Kreysig, E. 1998. Advanced Engineering Mathematics, eighth edition.New York: John Wiley & Sons.
Martin, C.M. and Houlsby, G.T. 1999. Jackup Units on Clay: StructuralAnalysis With Realistic Modelling of Spudcan Behaviour. Paper OTC 10996presented at the Offshore Technology Conference, Houston, 3-6 May. doi:10.4043/10996-MS.
Masing, G. 1926. Eigenspannungen und Verfertigung beim Messing.Proc., 2nd International Conference on Applied Mechanics, Zurich,Switzerland, 323-335.
Murff, J.D., Prins, M.D., Dean, E.T.R., James, R.G., and Schofield, A.N.1992. Jackup Rig FoundationModelling. Paper OTC 6807 presented at the Offshore Technology Conference,Houston, 4-7 may. doi: 10.4043/6807-MS.
Nelson, K., Smith, P., Hoyle, M., Stonor, R., and Versavel, T. 2000. Jack-up Response Measurements and theUnderprediction of Spud-Can Fixity By SNAME 5-5A. Paper OTC 12074 presentedat the Offshore Technology Conference, Houston, 1-4 May. doi:10.4043/12074-MS.
Newmark, N.M. 1959. A Method of Computation for Structural Dynamics.Journal of the Engineering Mechanics Division 85 (EM3):67-94.
Osborne, J.J., Trickey, J.C., Houlsby, G.T., and James, R.G. 1991. Findings From a Joint Industry Studyon Foundation Fixity of Jackup Units. Paper OTC 6615 presented at theOffshore Technology Conference, Houston, 6-9 May. doi: 10.4043/6615-MS.
Ott, E. 1993. Chaos in Dynamical Systems. Cambridge, UK: CambridgeUniversity Press.
Pyke, R. 1979. Nonlinear Soil Models for Irregular Cyclic Loadings.Journal of the Geotechnical Engineering Division 105 (6):715-726.
Schotman, G.J.M. 1989. TheEffects of Displacements on the Stability of Jackup Spud-Can Foundations.Paper OTC 6026 presented at the Offshore Technology Conference, Houston, 1-4May. doi: 10.4043/6026-MS.
SINTEF. 1996. Foundation Fixity Study for Jack-Up Units. Confidential ReportSTF22 F96660, SNAME OC-7 Panel, Jersey City, New Jersey (30 August 1996).
SNAME Technical & Research Bulletin 5-5A, Guidelines forSite-Specific Assessment of Mobile Jackup Units, Rev.1. 1991. Jersey City,New Jersey: Society of Naval Architects and Marine Engineers (SNAME).
SNAME Technical & Research Bulletin 5-5A, Guidelines forSite-Specific Assessment of Mobile Jackup Units, Rev. 2. 2002. Jersey City,New Jersey: Society of Naval Architects and Marine Engineers (SNAME).
