BIZOMAT MAKEOS · Mechanics
Wind Pressure and Force on a Surface
What force and overturning moment does wind at this speed put on this sign, guard or structure?
Dynamic pressure of wind from its speed and air density, the pressure on a surface with a shape (force) coefficient, the resulting force and its overturning moment about the base.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Wind speed | m/s | Design wind speed (from the applicable wind-load standard for structures). |
| Air density | kg/m³ | Air density; about 1.2 kg/m³ at sea level and 20 °C. |
| Shape (force) coefficient | Force coefficient for the shape (from the wind-load standard or test). | |
| Area facing the wind | m² | Projected area facing the wind. |
| Height of the area centre above the base | m | Lever arm from the base to the centre of pressure. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Wind speed
- What it is
- The speed of the wind striking the surface. For structures, the design wind speed for the site comes from the applicable wind-load standard.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0.000001 m/s to 200 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pressure and force rise with the square of speed: doubling the speed quadruples the force.
- Get it right
- Convert km/h to m/s by dividing by 3.6.
What this means: Air density
- What it is
- The density of the air, which falls with altitude and rising temperature; it scales the dynamic pressure of the wind.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 2 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pressure and force rise in proportion.
- Get it right
- Take it from a standard atmosphere table for the site altitude and temperature.
What this means: Shape (force) coefficient
- What it is
- A dimensionless coefficient for the shape of the body that converts the dynamic pressure of the wind into the net pressure on the area facing it.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pressure and force rise in proportion.
- Get it right
- Use the coefficient defined for the same reference area you enter, from the wind-load standard or a wind-tunnel test.
What this means: Area facing the wind
- What it is
- The projected area of the body as seen from the wind direction: its silhouette, not its total surface area.
- Units and format
- Enter a number in m²: square metres. The form accepts 0.000001 m² to 1000000 m². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 m² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The force and overturning moment rise in proportion.
What this means: Height of the area centre above the base
- What it is
- The height from the base, or the edge about which the object could tip, to the centre of the area facing the wind; it is the lever arm for the overturning moment.
- Units and format
- Enter a number in m: metres. The form accepts 0 m to 1000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The overturning moment rises in proportion; the force does not change.
Method and formulas
- Dynamic pressure q = ½ ρ V².
- Pressure on the surface p = C q; force F = p A; moment = F h.
- The handbook’s pressures (about 0.004 V² lb/ft² with V in mph) correspond to C ≈ 1.6 on this basis.
- Example: 20 m/s on 2 m² with C = 1.2 gives 576 N.
Limitations
- Steady wind; gusts and dynamic response are not included.
- Structures must be designed to the applicable wind-load standard.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check anchoring of an outdoor enclosure, sign or guard
- Estimate wind force on a crane load or panel being lifted
- Size fixings for a rooftop unit
Who it is for
- Structural engineers
- Rigging supervisors
- Site engineers
What you get
- Dynamic pressure
- Wind pressure and force
- Overturning moment
Interpreting the result
- Pressure rises with the square of speed: doubling the wind speed quadruples the force.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3028. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Roof loads, fixings and wind
In Rooftop Solar for Factories by the Numbers
What it covers: How to estimate the dead load of an array, the wind pressure and uplift on flush-mounted and ballasted modules, the loads on clamps and brackets, and the wind risk to modules during installation.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.