This paper presents uncertainties in spectral fatigue damages of offshore structures firstly. Then, attention is given to the formulation and procedure of a fast and efficient computation of fatigue reliability estimates. Most of uncertainties are embedded in response characteristics of the stress process and the damage-model used. Uncertainties in stress statistical characteristics are associated with the modeling of structures and random wave environment as well as wave loading and the analysis used. Uncertainties arising from degradation of member stiffness, wave-current and water-structure interactions can be considered in the modeling of structures, wave environment and loading. In the fatigue damage, there are additional uncertainties arising from the modeling of damage-mechanism. These uncertainties are due to experimental fatigue data and structural joint configurations. All these uncertainties can be classified into aleatory (naturally inherent) and epistemic (due to lack of knowledge) categories. The second part of the paper is devoted to a fast and efficient computation of fatigue reliability. This algorithm eliminates repetitive execution of spectral analysis procedure. It is performed only once for all reliability iterations. In this technique, a suitable spectral formulation of the stress process is used and a new uncertainty parameter is introduced to represent most of uncertainties in the stress spectrum. A detailed modeling of the fatigue-related uncertainties is presented. The failure function of the reliability analysis is expressed independently of the spectral analysis. The advanced FORM reliability method is used to calculate the reliability index and to identify important uncertainty parameters. The procedure is demonstrated by an example jacket structure and the results are compared with previously available ones.

1.
Wirsching, P.H. and Light, M.C., 1980, “Fatigue under wide band random stresses”, Journal of the Structural Div., ASCE, Vol.106, No.ST7.
2.
Karadeniz, H., 1990, “Fatigue analysis of offshore structures under non-narrow banded stress processes”, Proceedings of the First European Offshore Mechanics Symposium (EUROMS-90), Trondheim, Norway, August 20–23.
3.
Karadeniz, H., 1991, “An improved fatigue analysis for offshore structures”, Journal of Marine Structures, No.4, pp.333–352. Elsevier Science Publishers Ltd.
4.
de Back, J. and Vaessen, G.H.G., 1981, Fatigue and corrosion fatigue behaviour of offshore steel structures, ECSC Convention 7210-KB/6/602, Final Report, Dept. of Civil Engineering, Delft University of Technology, Delft.
5.
Karadeniz
H.
,
2001
, “
Uncertainty modelling in the fatigue reliability calculation of offshore structures
”,
Int. Journal of Reliability Engineering and System Safety
, December, Vol.
74
, No.
3
, pp.
323
335
.
6.
Barltrop, N.D.P. and Adams, A.J., 1991, Dynamics of fixed marine structures, Third edition, Butterworth-Heinemann Ltd., Oxford, U.K.
7.
Karadeniz, H., Vrouwenvelder, A. and Bouma, A.L., 1983, “Stochastic fatigue reliability analysis of jacked type offshore structures”, Proceedings of the NATO Advanced Study Institute on Reliability Theory and Its Application in Structural and Soil Mechanics, Edited by P.Thoft-Christensen, Martinus Nijhoff Publishers, The Hague.
8.
Gresnigt, AM, 1986, “Plastic design of buried steel pipelines in settlement areas,” Heron, Vol 31, No 4.
9.
Karadeniz
H.
,
1994
, “
An algorithm for member releases and partly connected members in offshore structural analysis
”,
Proc. 13th Int. Symp. Offshore Mechanics and Arctic Engineering (OMAE)
, Vol.
1
,
471
476
, Houston, Texas.
10.
Karadeniz, H., 2001, “Uncertainties in Spectral Fatigue Damages of Offshore Structures”, Proc. 20th Int. Symp. Offshore Mechanics and Arctic Engineering (OMAE), Paper No. S&R OMAE01-2118, Rio de Janeiro, BRAZIL.
11.
Karadeniz, H., 1992, “Stochastic analysis of offshore structures under wave-current and fluid-structure interactions”, Proceedings of the 11th International Conference on Offshore Mechanics and Polar Engineering (OMAE), Volume I-A, ASME, New York.
12.
Huang
N. E.
,
Chen
D. T.
,
Tung
C. C.
and
Smith
J. R.
,
1972
, “
Interactions between steady non-uniform currents and gravity waves with applications for current measurements
”,
Journal of Physical Oceanology
, Vol.
2
, pp.
420
431
.
13.
Brebbia, C.A. and Walker, S., 1979, Dynamic Analysis of Offshore Structures, Butterworth & Co. (Publishers) Ltd., London.
14.
API RP 2A, 1989, Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms, 18th. edition, American Petroleum Institute, Washington DC.
15.
Schutz, W., 1981, “Procedures for the prediction of fatigue life of tubular joints”, Proceedings of International Conference on Steel in Marine Structures, Paris, France, 5–8 October.
16.
CIRIA, 1976, Rationalisation of Safety and Serviceability Factors in Structural Codes, Report No. 63, Construction Industry Research and Information Association, London.
17.
Thoft-Christensen, P. and Baker, M.J., 1982, Structural Reliability Theory and Its Applications, Springer-Verlag, Berlin.
18.
Madsen, H.O., Krenk, S. and Lind, N. C., 1986, Methods of Structural Safety, Prentice Hall Inc., Englewood Cliffs.
19.
Melchers, R.E., 1999, Structural Reliability Analysis and Prediction, 2nd edition, John Willey & Sons, New York.
This content is only available via PDF.
You do not currently have access to this content.