This paper is concerned with structural reliability of an offshore guyed tower for large storm events. Analysis is conducted in the light of the failure of an anchor pile of the guy line system. Two failure modes for the extreme and the cyclic loadings at an anchor pile are considered. Dynamic analysis of the tower to random waves is earned out in the frequency domain utilizing the stochastic linearizations of the nonlinear mooring force and the nonlinear drag force. The probability of failure due to the extreme anchor load is evaluated based on the results of the dynamic analysis using the first-excursion probability analysis. For the consideration of the degradation of pile capacity due to cyclic loadings, empirical fatigue curves for a driven pile in clay are used. The numerical results indicate that the failure probability due to the cyclic loadings can be fairly comparable to the risk due to the extreme loading, particularly for the case where the mean safety level of the pile strength is low and the uncertainties in the pile resistance are large.


A reliability analysis of an offshore guyed tower for severe storm events is presented in this paper. More specifically, the reliability of an anchor pile of the guy line system is investigated. The guyed tower is one of the compliant structures recently developed for the deepsea oil production 1-3. Each line consists of a guyline catenary, a clump weight, an anchor line and an anchor pile. Under normal environmental conditions, the cable array acts as a hardening restraint. Under severe storm events, however, the clump weights are lifted from the seabed and the cable array acts as a softening restraint. This implies the geometric nonlinearity of the guyline system as in Fig. 2.

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