Effect of unsteady wind flow on galloping of tall prismatic structures

The galloping of tall prismatic cantilever type structures due to unsteady wind is solved analytically. The unsteady wind was considered by adding a t ime varying wind speed component to the mean wind speed component. In reali ty, the time-varying wind speed component is a random phenomenon that can b e modeled as a series of harmonic terms using the transformation of the uns teady wind speed spectrum into the time domain. In doing this it is apparen t that the structure is subjected to multiharmonic external and parametric excitations due to the unsteady wind in addition to the nonlinear self-exci ted wind forces due to the steady wind speed component. To have a clear ins ight into the unsteady wind effect, only one harmonic term is considered ou t of all the harmonic terms. The multiple-scale method is used to study the effect of primary and secondary resonances on the galloping response of th e structure. Comparisons between the analytical results obtained from the m ethod of multiple scales and the numerical solutions obtained from numerica l integration indicate the accuracy of the analysis and the comprehensive i nformation obtained from the analytical solutions.