IMPROVED SPECTRAL METHOD FOR VARIABLE AMPLITUDE FATIGUE PREDICTION

The dependence of fatigue damage accumulation on power spectral density (psd) is investigated for several types of random processes relevant to the stresses in offshore structures Representative data have been obtained from rainflow analysis of time histories simulated from both unimodal and bimodal psd functions These data are used to test the accuracy of spectral approximation methods in which the damage predictions are made from fairly simple calculational operations on the psd function Primary emphasis is placed on the commonly used Rayleigh approximation method and a new method that involves calculation of only one spectral moment (ie one integral of the psd) The new method is shown to be substantially more accurate than the Rayleigh approximation for some situations. © ASCE.