Wind Speed vs Wind Load

on 30 September 2024. Posted in Hydrology Engineering

Wind Speed

Definition - Wind speed is the rate at which air moves across the Earth's surface, typically measured in meters per second ($m/s$), kilometers per hour ($km/h$), or miles per hour ($mph$).
Measurement - It is often measured by an anemometer and is influenced by factors like geography, altitude, and local weather systems.
Relevance - Wind speed is a direct measurement of how fast the wind is blowing. It is an important factor for weather forecasting and is used to determine the potential forces acting on objects or structures exposed to wind.

Wind Load

Definition - Wind load is the force exerted by wind on a structure. It is a result of wind speed acting on the surface of buildings, towers, bridges, and other structures.
Relevance - Wind load is critical for engineering and architectural design, ensuring that structures can withstand the forces exerted by wind without failure.

Key Differences

"Wind speed" is a natural phenomenon, "wind wind" load is a calculated force based on the wind speed and how it interacts with structures.
"Wind speed" is measured directly, but "wind load" depends on the shape, size, and material of the structure. Higher wind speeds lead to greater wind loads on buildings or objects.

Wind speed measures how fast the wind is moving, while wind load measures the impact of that moving air on objects.

Wind Load (Generic Formula) Formula
$ F \;=\; A \; p_w \; C_d $
Symbol	English	Metric
$ F $ = Wind Load	$lbf$	$N$
$ A $ = Area	$ft^2$	$m^2$
$ p_w $ = Wind Pressure	$lbf\;/\;in^2$	$Pa$
$ C_d $ = Drag Coefficient	$dimensionless$	$dimensionless$

Wind Load (Electronic Industries Alliance) Formula
$ F \;=\; A \; p_w \; C_d \; Kz \; Gh $
Symbol	English	Metric
$ F $ = Wind Load	$lbf$	$N$
$ A $ = Area	$ft^2$	$m^2$
$ p_w $ = Wind Pressure	$lbf\;/\;in^2$	$Pa$
$ C_d $ = Drag Coefficient	$dimensionless$	$dimensionless$
$ Kz $ = Exposure Coefficient	$ft$	$m$
$ Gh $ = Gust Response Factor	$ft\;/\;sec$	$m\;/\;s$

Electronic Industries Alliance (EIA)

Wind Pressure (d_w) is found by calculating the wind speed ($v$) squared multiplied by 0.00256. The formula is $p_w = v^2 \; 0.00256$.
Exposure Coefficient (Kz) is found by calculating the height from the ground to the midpoint of the fixture/object ($z$) divided by $33^{2/7}$. The formula is $Kz = z \;/\; 33^{2/7}$.
Gust Response Factor ($Gh$) is calculated by entering the height ($h$) of the fixture/object into the following formula: $Gh = 0.65 + 0.60 \;/\; [\;(h\;/\;33) \;(1\;/\;7)\;]$.

Wind Load (Uniform Building Code) Formula
$ F \;=\; A \; P $ (Uniform Building Code) $ P \;=\; Ce \; Cq \; Qs \; Iw $
Symbol	English	Metric
$ F $ = Wind Load	$lbf$	$N$
$ A $ = Area	$ft^2$	$m^2$
$ P $ = Wind Pressure	$lbf\;/\;in^2$	$Pa$
$ Ce $ = Combined Height Exposure	$ft$	$m$
$ Cq $ = Pressure Coefficient ($C_d$ Drag Coefficient)	$dimensionless$	$dimensionless$
$ Qs $ = Wind Stagnation Pressure	$mph$	$kph$
$ Iw $ = Importance Factor	$dimensionless$	$dimensionless$

Uniform Building Code (UBC)

Combined Height Exposure (Ce) - Combined height, exposure, and gust response factor.

Exposure B - The terrain with buildings, trees or other surface irregularities covering at least 20 percent of the surrounding area and extending 1.6 kilometers or more from the site.
Exposure C - Has terrain that is flat and generally open, extending 0.8 km or more from the site.
Exposure D - Is the most severe, with basic wind speeds of 129 km/hr or greater and terrain that is flat and unobstructed facing large bodies of water.

Wind Stagnation Pressure (Qs) - Qs is equivalent to the wind pressure calculation $Qs = 0.00256 \; V^2$, where $V$ is the wind speed in miles per hour (mph).

Importance Factor (Iw) - Can be determined using table in UBC. It is a multiplier used in calculating loads that takes into account the use of the building. If a building contains hazardous materials, its importance factor will be higher than that of a traditional building.

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Tags: Hydrology

Wind Load (Generic Formula) Formula
\( F \;=\; A \; p_w \; C_d \)
Symbol	English	Metric
\( F \) = Wind Load	\(lbf\)	\(N\)
\( A \) = Area	\(ft^2\)	\(m^2\)
\( p_w \) = Wind Pressure	\(lbf\;/\;in^2\)	\(Pa\)
\( C_d \) = Drag Coefficient	\(dimensionless\)	\(dimensionless\)

Wind Load (Electronic Industries Alliance) Formula
\( F \;=\; A \; p_w \; C_d \; Kz \; Gh \)
Symbol	English	Metric
\( F \) = Wind Load	\(lbf\)	\(N\)
\( A \) = Area	\(ft^2\)	\(m^2\)
\( p_w \) = Wind Pressure	\(lbf\;/\;in^2\)	\(Pa\)
\( C_d \) = Drag Coefficient	\(dimensionless\)	\(dimensionless\)
\( Kz \) = Exposure Coefficient	\(ft\)	\(m\)
\( Gh \) = Gust Response Factor	\(ft\;/\;sec\)	\(m\;/\;s\)

Wind Load (Uniform Building Code) Formula
\( F \;=\; A \; P \) (Uniform Building Code) \( P \;=\; Ce \; Cq \; Qs \; Iw \)
Symbol	English	Metric
\( F \) = Wind Load	\(lbf\)	\(N\)
\( A \) = Area	\(ft^2\)	\(m^2\)
\( P \) = Wind Pressure	\(lbf\;/\;in^2\)	\(Pa\)
\( Ce \) = Combined Height Exposure	\(ft\)	\(m\)
\( Cq \) = Pressure Coefficient (\(C_d\) Drag Coefficient)	\(dimensionless\)	\(dimensionless\)
\( Qs \) = Wind Stagnation Pressure	\(mph\)	\(kph\)
\( Iw \) = Importance Factor	\(dimensionless\)	\(dimensionless\)

Wind Load (Generic Formula) Formula

Wind Load (Electronic Industries Alliance) Formula

Wind Load (Uniform Building Code) Formula

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