RELIABILITY OF OFFSHORE GUYED TOWER AGAINST ANCHOR PILE FAILURE

Abstract

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 guyline system. Two failure modes, for the extreme and the cyclic loadings at an anchor pile, are considered. Dynamic analysis of the response of the tower to random waves is carried 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 compared 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.