Sensitivity Analysis of Selected Random Variables of Existing Offshore Jacket Structures in Persian Gulf

Authors

1 Prof, K. N. Toosi University of Technology and TWI Persia

2 Structural Integrity Section, TWI Persia

3 Senior Structural Engineer

Abstract

Structural integrity evaluation of an existing offshore platform typically is based on a combination of non-linear structural analysis together with risk and reliability analysis. Quantitative assessment of the probability of failure of a jacket platform under extreme metocean loads is a multi-disciplinary task, poses significant challenges and involves a large number of uncertainties regarding the metocaen hazards, structural system and modelling, loads, material behaviour and geotechnical information. The probability of failure is commonly estimated using a reliability analysis to account for uncertainties in derivation of both the loading and the strength.
Different sources of uncertainties contribute to the platform ultimate strength. Sensitivity analysis should be carried out to provide quantitative information necessary for classifying random variables according to their importance. These measures are essential for reliability-based service life prediction of deteriorating materials and structures. Accordingly, in this paper, Tornado approach has been used to identify those variables that affect the failure most so that more research can focus on those variables. To this end, six existing offshore platforms located in Persian Gulf are investigated. The results have been presented in the form of a Tornado diagram which will graphically show the sensitivity of the target function to each random variable.

Keywords


[Ref. 1] Zeinoddini, M., Ranjbar, P., et al., “Remaining Fatigue Life Assessment of Aging Fixed Steel Offshore Jacket Platforms”, Accepted in Journal of Structure and Infrastructure Engineering. [Ref. 2] Golpour, H., Zeinoddini, M., et al., “Structural Integrity Assessment of Aging Fixed Steel Offshore Jacket Platforms: A Persian Gulf Case Study”, ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering, Nantes, France, June 9–14, 2013, OMAE2013-10712, pp. V02AT02A055. [Ref. 3] Zeinoddini M, Ahmadi I, Khalili H, Golpour H, Nikoo MH , “Fatigue Life Assessment of Pinned Connections in an Aging Jacket Platform”, 6th International Offshore Industries Conference, 4 and 5 May 2015 – Tehran, Sharif University of Technology. [Ref. 4] Hezarjaribi M, Bahaari MR, Bagheri V, Ebrahimian H. Sensitivity analysis of jacket-type offshore platforms under extreme waves. Journal of Constructional Steel Research 2013; 83: 147-155. [Ref. 5] Saltelli A., Annoni P., Azzini I., Campolongo F., Ratto M., Tarantola S., “Variance based sensitivity analysis of model output. Design and estimator for the total sensitivity index”, Computer Physics Communications, Volume 181, Issue 2, February 2010, Pages 259–270. [Ref. 6] Tian W., “A review of sensitivity analysis methods in building energy analysis”, Renewable and Sustainable Energy Reviews, Volume 20, April 2013, Pages 411–419. [Ref. 7] Wainwright H., Finsterle S., Jung Y., Zhou Q., Birkholzer J., “Making sense of global sensitivity analyses”, Computers & Geosciences, Volume 65, April 2014, Pages 84–94. [Ref. 8] Rodriguez G., Carrillo A., Dominguez F., Lopez J., Zhang Y., “Uncertainties and sensitivity analysis in building energy simulation using macroparameters”, Energy and Buildings, Volume 67, December 2013, Pages 79–87. [Ref. 9] Saltelli, A., Tarantola, S., Campolongo, F., and Ratto, M. (2004). Sensitivity analysis in practice: A guide to assessing scientific models, Wiley, New York. [Ref. 10] Kong J. S., and Frangopol D. M., (2005), Sensitivity Analysis in Reliability-Based Lifetime Performance Prediction Using Simulation, Journal of Materials in Civil Engineering, Vol. 17, No. 3, June 1. [Ref. 11] Porter, K.A. (2003). An Overview of PEER’s Performance-Based Earthquake Engineering Methodology. Conference on Applications of Statistics and Probability in Civil Engineering (ICASP9), Civil Engineering Risk and Reliability Association (CERRA), San Francisco, CA, July 6-9, 2003. [Ref. 12] Porter, K.A., J.L. Beck, and R.V. Shaikhutdinov (2002). Sensitivity of building loss estimates to major uncertain variables. Earthquake Spectra, 18 (4), 719-743. [Ref. 13] Porter, K.S. “A Beginner’s Guide to Fragility, Vulnerability, and Risk”, University of Colorado Boulder and SPA Risk LLC, Denver CO USA. [Ref. 14] Bentley Systems, SACS Suite program, version 5.3, 2011. [Ref. 15] NORSOK Standard N-006, “Assessment of structural integrity for existing offshore load, bearing structures”, Edition 1, March 2009. [Ref. 16] American Bureau of Shipping (ABS), “Commentary on the Guide for Buckling and Ultimate Strength Assessment for Offshore Structures”, ABS Plaza, Houston, TX, USA, March 2005. [Ref. 17] Gerwick, “Construction of Marine and Offshore Structures”, 2007. [Ref. 18] American Petroleum Institute, “Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms - Working Stress Design”, API RP 2A-WSD, 21st Edition, Supplements 2-3, October 2007. [Ref. 19] CEN, EUROCODE 3, “Design of Steel Structures, General Rules and Rules for Buildings”, European Committee for Standardization, 2005. [Ref. 20] Skallerud, B., Amdahl, J. (2002). Nonlinear analysis of offshore structures. Research studies Press Ltd, Bldock, Hertfordshire, England. [Ref. 21] JCSS. (2001). Probabilistic Model Code - Part 1: Basis of Design. (12th draft). Joint Committee on Structural Safety, March 2001. [Ref. 22] Hansen, P.F., Madsen H.O., Tjelta T.I. (1995). Reliability analysis of a pile design, Journal of Marine Structures 8(2): 171-198. [Ref. 23] Baecher, G.B., Christian, J.T. (2003). Reliability and Statistics in Geotechnical Engineering. John Wiley and Sons.