Reference Wind Pressure or Design Wind Speed
Specifies the NBC Reference Wind Pressure. The reference velocity pressure q is the appropriate value determined in conformance with Subsection 1.1.3 (based on probability) or Table C-1.
Specifies the design value of the wind speed. This varies according to geographical location and according to company or vendor standards. Typical wind speeds in miles per hour are 85.0, 100.0, 110.0, and 120.0.
Typical units (depending on your unit system):
-
ft/sec
-
m/sec
-
mm/sec
Type the lowest value reasonably allowed by the standards you are following because the wind design pressure (and thus force) increases as the square of the speed.
Importance Factor (Iw)
Specifies the NBC importance factor. This value is the importance factor for wind taken from the table below. This is table 4.1.7.1 on page 4-17 of Division B of NBC 2005.
Importance Category |
Importance Factor, Iw |
|
---|---|---|
ULS |
SLS |
|
Low |
0.8 |
0.75 |
Normal |
1.0 |
0.75 |
High |
1.15 |
0.75 |
Post Disaster |
1.25 |
0.75 |
Exposure Constant
Based on the profile of mean wind speed, the Exposure Constant varies considerably with the general roughness of the terrain over which the wind has been blowing before it reaches the building. These exposures are applicable only under the dynamic (detailed) method, whereas the terms open and rough were used for the static (simplified) method.
Exposure A - (Open or Standard Exposure) - Indicates open-level terrain with only scattered buildings, trees, or other obstructions, open water or shorelines. Reference wind speeds are based on Exposure A.
Exposure B - (Rough Exposure) - Indicates rough terrain, such as large cities with several and dense high-rise buildings, which persists in the upwind direction for at least 20 times the building height. Prior to NBC 2010, referred to winds that persist in the upward direction for 1.0 km or 10 times the building height, whichever is larger.
Exposure C - (NBC 2005 only) - Rough terrain, such as large cities with several and dense high-rise buildings, which persists in the upwind direction for at least 1.0 km or 10 times the building height, whichever is larger.
Roughness Factor
Specifies the Roughness Factor:
1 - Round, moderately smooth
2 - Round, rough (D'/D = 0.02)
3 - Round, very rough (D'/D = 0.08)
Height of the Windward Face
Specifies the height of a piping section that is exposed to wind blow.
Structural Damping Coefficient
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.
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.