In this study two aspects of the fatigue analysis of fixed offshore structures subjected to random waves are investigated. The one is related to the fatigue life and the other is to the fatigue reliability. For the estimation of the fatigue life, two methods based on the narrow band and the wide band assumptions of stress time histories are studied. For the evaluation of the fatigue reliability, the uncertainties associated with the Palmgren-Miner's hypothesis, the fatigue data, the stress analysis procedure and the narrow bandedness of the stress are considered.
Example analysis have been carried out for various seastate conditions using a fixed offshore structure in 700ft water. Numerical results include the RMS values of the structural responses, the fatigue life, the narrow band correction factors and the fatigue reliability index.