Multivariate Distributions of Directional Wind Speeds

The probability of failure of a structure or structural element subjected to wind forces depends, in large part, on the distribution of extreme wind speeds acting on the structure. In the past, distributions of extreme wind speeds were based on extreme wind data without regard to wind direction, and probabilities of failure were computed accordingly. A method is presented herein for calculating failure probabilities by using directional wind speed data as obtained from weather station records. The method takes advantage of the weak correlations found among wind speeds from different directions and the property of extreme value random variables that zero correlation implies statistical independence. The method is applicable to any type of structure, including structures exhibiting aerodynamic amplification or aeroelastic effects. In addition, it is shown that, in practice, the necessary distributions can be estimated almost as accurately from data obtained from readily available published documents as from data obtained from original weather records.