Wind Hazard Risk Assessment and Management for Structures

Chapter 2. Structural Components and Wind Directionality 28
distribution parameters by Iman et al. (2002) and assuming that s is uniformly distributed
from -200 km to 200 km. This results in three collections of simulated wind time series
in which the tropical cyclone track is at most 200 km away from the structure. Note
that since the entire analytical model involves only algebra, a large number of simulated
wind time series can be generated with scant computational effort. The three wind time
series databases are then employed to calculate the wind pressure over time associated with
each pressure coefficient. Each database, generated with the category 1, 3 or 5 hurricane
parameters, consists of 10,000 wind time series and represents the scenario in which the
tropical cyclone track is at most 200 km from the structure. The angle in which the
tropical cyclone approaches the structure is assumed to be uniformly distributed within
[0, 2π]. For each wind time series, we fix the absolute wind direction and let the orientation
of the structure be one of the 24 evenly spaced angles across [0, 2π]. As a result, 240,000
individual wind velocity time series are considered for each hurricane category.
Figure 2.6 shows the cumulative distribution functions of maximum wind pressure over
time using the hurricane-category-5 simulated wind time series database. In each plot, the
solid line is the cumulative distribution of the maximum wind pressure over time (Smax)
obtained by the time-stepping method, and the dashed line is the cumulative distribution
of wind pressure at maximum wind speed (S ∗ ) obtained by the point-in-time approach.
The mean values of both distributions are shown in the plots. The cumulative distributions
using hurricane categories 1 and 3 are not shown due to space constraints.
The difference between Smax and S ∗ , indicating the degree of inaccuracy of the point-
in-time approach, varies with the pressure coefficient. To compare the two cumulative
distributions of each wind pressure quantitatively, the Kolmogorov-Smirnov statistic is cal-
culated. It is defined (Kendall et al., 1999) as the largest absolute difference between two