Civil Engineering Reference
In-Depth Information
For synoptic winds:
(2.19)
For downburst winds:
(2.20)
The combined probability of exceedence of a given gust speed from either type of wind is
obtained by substituting in Equation (2.3):
(2.21)
Equations (2.19), (2.20) and (2.21) are plotted in Figure 2.4. The lines corresponding to
Equations (2.19) and (2.20) cross at a return period of 30 years. It can also be seen that
the combined wind speed return period relationship is asymptotic to the synoptic line at
low return periods and to the downburst line at high return periods.
2.5
Parent wind distributions
For some design applications it is necessary to have information on the distribution of the
complete population of wind speeds at a site. An example is the estimation of fatigue
damage for which account must be taken of damage accumulation over a range of wind
storms (see Section 5.6). The population of wind speeds produced by synoptic wind
storms at a site is usually fitted with a distribution of the Weibull type:
(2.22)
