Having summarized briefly uncertainties in spectral fatigue damages of offshore structures, this paper presents the formulation and procedure of an efficient computation of reliability estimates on basis of fatigue damages and stresses. 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, random wave environment, wave loading and the analysis used. In the fatigue damage, additional uncertainties arise 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 the categories as a) those naturally inherent (aleatory) and b) those due to lack of knowledge (epistemic). The second part of the paper is devoted to a fast and efficient computation of the fatigue reliability. This algorithm prevents repetitive execution of spectral analysis procedure during the reliability iteration. In this technique, a suitable formulation of the stress spectrum is used with a model uncertainty parameter representing most of uncertainties in the stress spectrum. The failure function of the reliability analysis is expressed independently of the spectral analysis. For the stress based reliability calculation the mean stress-amplitude of the stochastic stress variation is used to define a limit state function. The related uncertainties are the same as those aforementioned. 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. The third part of the paper explains the inverse reliability method to determine some parameters, which may be deterministic or probabilistic, under required reliability constraints.

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