Wind Load Parameters
Basic Wind Speed
Typical units (depending on your unit system):
-
ft/sec
-
m/sec
-
mm/sec
Specifies the three-second gust speed at 33 ft. (10 m.) above ground for Exposure C category as determined according to Section 6.5.6.3.
According to ASCE 7, the following are typical basic wind-speed values:
-
California and West Coast Areas -124.6 ft./sec. (85 mph)
-
Rocky Mountains - 132.0 ft./sec (90 mph)
-
Great Plains - 132.0 ft./sec (90 mph)
-
Non-Coastal Eastern United States -132.0 ft./sec (90 mph)
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Gulf Coast - 190.6 ft./sec (130 mph)
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Florida-Carolinas - 190.6 ft./sec (130 mph)
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Miami - 212.6 ft./sec (145 mph)
-
New England Coastal Areas - 176.0 ft./sec (120 mph)
Wind Exposure
Specifies the wind exposure. This value is the exposure category that adequately reflects the characteristics of ground surface irregularities. The ASCE 7 code standard (found in ASCE 7 2005, Section 6.5.6.3 and ASCE 7 2010, Section 26.7.3) defines exposure categories as follows:
B or 2
Exposure B. Urban, suburban, and wooded areas, prevailing. For upwind distance requirements, refer to the code standard.
C or 3
Exposure C. All cases where exposures B and D do not apply.
D or 4
Exposure D. Flat coastal areas, prevailing. Urban, suburban, wooded, or open terrain areas with scattered obstructions. For upwind or downwind requirements, refer to the code standard.
-
See ASCE 7 2005 (Section 6.5. 6.3) and ASCE 7 2010 (Section 26.7.3) for any exceptions
on wind exposures.
Structural Damping Coeff.
Specifies the structural damping coefficient. This value is the percentage of critical damping and is used to calculate the gust factor for the wind load calculations.
Structural Classification
Specifies the classification of buildings and structures based on the type of occupancy.
ASCE 7-2005 Table 1-1, classification is as follows:
1 - Category I
Failure represents low hazard.
2 - Category II
All structures except 1, 3, and 4.
3 - Category III
Primary occupancy more than 300 people.
4 - Category IV
Essential facilities (Hospitals, and so forth)
1, 2, 3 and 4 are the options for structural classification categories, and are equivalent to categories
I, II, III and IV defined in ASCE 7.
Importance Factor
Specifies the importance factor (I). This value is used to calculate the velocity pressure for wind load calculations. The importance factor depends on the structural classification and whether the region is prone to hurricanes, as shown below.
For ASCE 7 2010, CAESAR II sets the importance factor to 1, as the code standard no longer addresses this factor.
For ASCE 7 2005, set the importance factor as per the code standard in Table 6-1.
|
Category |
Non-Hurricane |
Hurricane Prone |
|---|---|---|
|
1-I |
0.87 |
0.77 |
|
2-II |
1.00 |
1.00 |
|
3-III |
1.15 |
1.15 |
|
4-IV |
1.15 |
1.15 |
1, 2, 3, and 4 are the options for structural classification categories, and are equivalent to categories
I, II, III and IV, defined in ASCE 7.
Structure Natural Frequency
Specifies the natural frequency used to calculate the dynamic wind gust effect factor for dynamically sensitive structures. (f < 1 Hz.)
If the natural frequency is not defined, CAESAR II uses a gust effect factor 0.85.
Ground (System) Elevation Above Sea Level
Specifies the ground elevation factor used to adjust for air density, determined according to Section 26.9 of ASCE 7 (2016).
Topographic Factor Parameters
Height of Hill or Escarpment
Specifies the height of hill or escarpment value. This value is the height relative to the upwind terrain. It is used in calculations of the topographic factor of structures sited on the upper half of hills and ridges or near the edges of escarpments.
Crest Distance
Specifies the distance upwind of crest to where the difference in ground elevation is half the height of hill or escarpment.
Distance from Crest to Site
Specifies the distance upwind or downwind from the crest to the building site.
Hill Type
Specifies the hill type. This value is the hill type is defined as follows:
0
No Hill
1
2D Ridge
2
2D Escarpment
3
3D Axisymmetric Hill
For more information on using wind reduction factors with ASCE 7, see ASCE 7/IBC Wind and Seismic Load Combinations.