Rainflow counting is widely accepted as the method that is most suited to analysis of fatigue damage of materials submitted to irregular loading. Formulas such as the Wirsching-Light and the Dirlik one allow to take into account spectral shape and bandwidth in an empirical or semi-empirical manner to obtain a best estimate damage reduction of the rainflow counting with respect to the narrow-band approximation. However, if one considers parametric shape families of common use for the spectra, a more straightforward way is to make damage depend on the shape parameter of the family rather than on the spectral moments. We provide here such semi-empirical parametric formulas for the Jonswap, Wallops, Triangle and Power-tail families. In addition, the ICA formula allows us to extend the above formulas to the well-known bimodal spectral shape proposed by Ochi-Hubble.

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