The Peak Factor for Gust Loading: A Review and Some New Proposals

Abstract

Abstract. Wind forces on structures that can be considered stiff are usually calculated by using the so-called gust factor G that magnifies the effects of the statical part of the wind speed U. In the expression of G a peak factor g is introduced to account for the maxima of the response dynamical displacement Xd(t),which is a zero mean stationary Gaussian process. The peak factor is derived by assuming that the upcrossings of a given level are a Poisson process, which is deemed very conservative by several authors. Thus, other ways for computing g are proposed herein, preserving its classical definition. They are: (1) the use of the envelope of the response process; (2) the solution of the backward Kolmogorov equation; (3) the use of some approximate formulae such as those by Preumont, Lutes et al., and Vanmarcke. The theoretical models are applied to the response of a linear SDOF oscillator for two values of the ratio of critical damping. In the last part of the paper a nonlinear response, that of a Duffing oscillator, is considered and the problem of the peak factor for this nonlinear case is attacked by using the stochastic averaging of energy envelope. The results of the various approaches are compared with those obtained by numerical simulation.