BIZOMAT MAKEOS · Mechanics
Wind Load on a Sign or Panel Post (Force, Base Moment, Stress, Deflection)
What wind force does this sign or panel take, what bending stress does it put in the supporting tube post, and how far does the top deflect?
Check of a panel, sign or guard on a single cantilever round-tube post: dynamic pressure, surface pressure, wind force and the base overturning moment (as the wind pressure tool), the post’s second moment and section modulus, bending stress at the base, deflection at the panel centre treating the wind as a point load there, and checks against your allowable stress and deflection limit.
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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 (gust) at the panel height (from the wind code for the site; your value). |
| Air density | kg/m³ | Air density. |
| Force coefficient | Force (drag) coefficient for the panel shape (about 1.2 for a flat sign; from the wind code). | |
| Panel area | m² | Area of the panel facing the wind. |
| Height of the panel centre above the base | m | Height from the post base to the centre of the panel. |
| Post outside diameter | mm | Outside diameter of the tube post. |
| Post wall thickness | mm | Wall thickness of the post. |
| Post elastic modulus | GPa | Elastic modulus of the post. |
| Allowable bending stress | MPa | Allowable bending stress for the post (your design value). |
| Largest deflection as a fraction of height (1 ÷ …) | Deflection limit expressed as height divided by this number (100 means h/100). |
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 design wind speed at the sign, from the wind loading standard that applies to the site or from site data.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0.000001 m/s to 100 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
- Wind force, base moment and stress rise with the square of the speed.
What this means: Air density
- What it is
- The density of the air, used to turn wind speed into dynamic pressure.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.5 kg/m³ to 1.5 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.
- Get it right
- Air density falls with altitude and temperature; use the value your wind standard specifies.
What this means: Force coefficient
- What it is
- The force (drag) coefficient of the panel shape, which turns dynamic pressure into the pressure acting on the panel face.
- Units and format
- Enter a plain number with no unit. The form accepts 0.1 to 3. 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
- Wind force rises in direct proportion.
- Get it right
- Take it from the wind standard for your panel shape and proportions.
What this means: Panel area
- What it is
- The face area of the sign or panel exposed to the wind.
- Units and format
- Enter a number in m²: square metres. The form accepts 0.000001 m² to 1000 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
- Wind force, moment and stress rise in direct proportion.
- Get it right
- The post itself is not included; add its projected area if it is significant.
What this means: Height of the panel centre above the base
- What it is
- The height from the post base (ground or base plate) to the centre of the panel area, where the wind force is taken to act.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 100 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 base moment rises in proportion, and deflection with the cube of this height.
What this means: Post outside diameter
- What it is
- The outside diameter of the round hollow post.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 114.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The section modulus rises steeply with diameter, so a slightly larger post lowers stress and deflection a lot.
- Get it right
- Use the actual tube outside diameter, not the nominal pipe size.
What this means: Post wall thickness
- What it is
- The wall thickness of the round hollow post.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the actual wall, less any corrosion loss you need to allow for.
What this means: Post elastic modulus
- What it is
- The elastic modulus of the post material, from material data. It affects the deflection result only, not the stress.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 400 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Allowable bending stress
- What it is
- The bending stress the post may carry under this wind load, from your design standard and the material’s strength.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 2000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Largest deflection as a fraction of height (1 ÷…
- What it is
- The deflection limit written as height divided by the allowed deflection at the panel; a larger number allows less movement.
- Units and format
- Enter a plain number with no unit. The form accepts 10 to 1000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type only the number under the line in “height ÷ …”, not the deflection itself.
Method and formulas
- q = ½ ρ V²; p = C_d q; F = p A; base moment M = F h (as the wind pressure tool).
- Tube I = π (D⁴ − d⁴) ÷ 64; Z = I ÷ (D ÷ 2); stress σ = M ÷ Z.
- Deflection at the panel centre δ = F h³ ÷ (3 E I).
- Example: 20 m/s on 2 m² gives 576 N and 1,728 N·m at the base; the post runs at 46.789 MPa and deflects 12.281 mm.
Limitations
- Single post with a rigid base; base plate, bolts and footing need their own checks.
- Wind on the post itself and dynamic (gust) response are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a post for a sign, screen or guard
- Check an outdoor panel for a design wind speed
- Check a machine guard against wind or air blast
Who it is for
- Design engineers
- Structural engineers
- Plant engineers
What you get
- Pressure, force and base moment
- Post section and base bending stress
- Deflection at the panel against the limit
Interpreting the result
- Deflection often governs tall single posts before stress does.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3028, 257–277. Topic reference; no source tables or recommended settings are reproduced.
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Open the Wind Load on a Sign or Panel Post (Force, Base Moment, Stress, Deflection) calculator