Wind Hazard Risk Assessment and Management for Structures

Chapter 2. Structural Components and Wind Directionality 18
determined by a professional team in the Florida Commission on Hurricane Loss Projection
Methodology. For example, the statistical measures (lower limit, mode and upper limit) of
Vt, ∆P and Rmax for a category 5 hurricane are (4.5, 6.75, 9) (85, 95, 105) and (8, 20, 40),
respectively.
Table 2.1: Probability distribution of tropical cyclone parameters.
Parameter Symbol Unit Category 1 Category 3 Category 5
Translational velocity Vt m/s
Central pressure difference ∆P mB
Radius of maximum wind Rmax km
2.2.3 Tropical Cyclone Track
a = 4.5
b = 6.75
c = 9
a = 15
b = 22.5
c = 30
a = 20
b = 35
c = 64
a = 4.5
b = 6.75
c = 9
a = 45
b = 57.5
c = 60
a = 13
b = 32
c = 64
a = 4.5
b = 6.75
c = 9
a = 85
b = 95
c = 105
a = 8
b = 20
c = 40
Two simplifying assumptions are made in modeling the tropical cyclone track. First, for
the purpose of estimating the wind damage to an individual structure, it is unnecessary
to track the tropical cyclone from genesis to dissipation. We are only interested in the
time period when the wind speed is above a certain threshold (below which damage is
highly unlikely). It is assumed that the tropical cyclone track remains straight during this
relatively short time period. Second, we are interested in the wind angle relative to the
structure’s orientation, not the absolute wind angle with respect to the cardinal directions;
therefore the absolute translational direction of the tropical cyclone does not matter.
Based on these assumptions, the location of the tropical cyclone track can be fully
defined by the closest distance between the track and the structure, denoted herein by s. A
plus or minus sign is assigned to the quantity s to indicate whether the structure is on the