NBC Wind Code Options - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
13

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.

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

Indicates open-level terrain (open or standard exposure) with only scattered buildings, trees, or other obstructions, open water or shorelines. Reference wind speeds are based on Exposure A.

Exposure B

Indicates rough terrain (rough exposure), 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.