THE PEAK FACTOR FOR GUST LOADING - A REVIEW AND SOME NEW PROPOSALS

Wind forces on structures that can be considered stiff are usually cal culated by using the so-called gust factor G that magnifies the effect s of the statical part of the wind speed U. In the expression of G a p eak factor g is introduced to account for the maxima of the response d ynamical displacement X-d(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 conservat ive 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 at, and Vanmarcke. The theoretical models are applied to the response of a linear SDOF oscillator for two value s of the ratio of critical damping. Tn the last part of the paper a no nlinear response, that of a Duffing oscillator, is considered and the problem of the peak factor for this nonlinear case is attacked by usin g the stochastic averaging of energy envelope. The results of the vari ous approaches are compared with those obtained by numerical simulatio n.