Wind-induced fatigue of structures under neutral and non-neutral atmospheric conditions

The authors of this paper have carried out a wide research project aimed at determining the wind-induced fatigue of structures, hypothesising the wind field as neutrally stratified, as it is typical of evaluations addressed to ultimate loading conditions. As wind-induced fatigue is sensitive to moderate wind velocities, for which stable or unstable atmospheric conditions can occur, this paper extends the procedures previously established to non-neutral thermal stratifications. The mean wind velocity profile and the cross-power spectral density functions of the atmospheric turbulence are expressed in terms of the Monin–Obukhov length. The occurrence of stable, unstable and neutral conditions is taken into account by means of the joint probability distribution of the mean wind velocity and direction and of the Monin–Obukhov length. The effects of non-neutral stratifications on the structural response and on the mean fatigue life are preliminary discussed with reference to an example concerning a steel chimney.