Confidence in the long-term use of jack-up platforms in deep water and harsh environments requires appropriate models for their assessment under dynamic loading conditions. In this paper probabilistic models are used to develop further understanding of this assessment. Particular emphasis is placed on achieving a balanced approach in considering the non-linearities and uncertainties in the structure, foundations and wave loading. A method of calculating short-term extreme response statistics, while including variability in parameters, is briefly outlined, and a numerical experiment for typical central North Sea conditions detailed. Long-term extreme response statistics are also evaluated, and the quantitative influence of the probabilistic formulations of the variables (as opposed to deterministic values) shown.


Most analysis of jack-up units use deterministic models, i.e. the material and geometric properties, loading conditions and actions are uniquely specified. It is known, however, that there are parameters within the models that are not unique, but have a range of possible values. By using a probabilistic formulation of one or more of the material properties, geometric dimensions or the actions on the structure, the likelihood that the jack-up behaves in a certain way can be more "realistically" evaluated. Within this paper, probabilistic methods are used to develop an understanding of the response behaviour of jackups. In structural reliability theory, the failure probability of one component is defined as (equation 1 shown in paper) where G(X) is the failure function (G(X)< 0 is a failure state and G(X) > 0 a safe state), X is a set of k random basic variables, i.e. [X]-- [X l, X2..... Xk] and fx (X) the multi-variant density function of X. For a component reliability analysis, failure criteria are usually set on the limiting factors of strength or behaviour of the jack-up and are of the form:

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