Signboard wind force to EN 1991-1-4 Section 7.4.3: force, overturning and torsional moments at the base, with the eccentricity. Run the free template.
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About this Signboard Wind Force Calculator
This calculator gives the total wind force on a signboard, with the overturning and torsional moments at its base, to EN 1991-1-4 Section 7.4.3 using the recommended values with no National Annex. The peak velocity pressure is worked at the centre of the board, the force coefficient applies to a board held clear of the ground by at least a quarter of its height, and the resultant acts with a horizontal eccentricity so the supports carry shear, overturning and torsion together.
- Sign structure designer sizes posts, footings and baseplates for billboards and pylon signs from the base force and moments.
- Building services or facade engineer checks a roof-mounted or elevated sign and its fixings back to the supporting structure.
- Certifying engineer reviews a sign submission against Section 7.4.3, with the clearance check and eccentricity set out on the page.
The force, moments, peak velocity pressure and force coefficient are reported together with a pass or fail clearance check. It is an engineering-grade calculation you can duplicate and adapt in a CalcTree workspace.
More info on Signboard Wind Force
Reference height and area
Section 7.4.3 takes the reference height at the centre of the board, the height of its bottom edge plus half the board height, not at its top. The reference area is the full board, its width times its height. The peak velocity pressure is worked at the reference height from Section 4.
Clearance and force coefficient
A board whose bottom edge is at least a quarter of its height above the ground takes the Section 7.4.3 force coefficient. Below that clearance the board behaves as a free-standing wall (Section 7.4.1), the page falls back to a non-Section 7.4.3 value, and the clearance check fails so the case is not missed.
Force, overturning and torsion
The force is the structural factor times the force coefficient, the peak velocity pressure and the reference area (Eq. 5.3). It acts at the reference height, so the overturning moment at the base is the force times that height. The resultant is offset horizontally from the centre of the board by an eccentricity, a fraction of the width set as a Nationally Determined Parameter (Section 7.4.3(2)), which gives a torsional moment at the base. Check both senses.
Common Calculation Errors to Avoid
- Taking the reference height at the top of the board Section 7.4.3 uses the centre of the board. Using the top overstates the peak velocity pressure and puts the force at the wrong lever arm for the overturning moment.
- Leaving out the torsion The eccentric resultant twists the supports, and the eccentricity grows with the board width. Both senses of the eccentricity need checking.
- Applying the signboard coefficient to a low board A board closer to the ground than a quarter of its height is a free-standing wall under Section 7.4.1, with zoned net pressure coefficients rather than a single force coefficient.
- Using the mean pressure for cladding The mean wind pressure on the board is for the global design of the board and its supports. Panels and fixings need local pressure coefficients.
- Skipping the National Annex The eccentricity fraction and the wind parameters are nationally determined. Check the National Annex for the country of use before relying on the recommended values.
Engineering templates
Common calculators
Design guides
FAQs
Why is the reference height at the centre of the board?
That is where Section 7.4.3 places it, together with a reference area equal to the full board. The force acts at that height, so the overturning moment at the base uses it as the lever arm.
What happens if the board is close to the ground?
If the bottom of the board is less than a quarter of its height above the ground, Section 7.4.3 does not apply and the board is treated as a free-standing wall under Section 7.4.1. The page flags this with a failed clearance check.
Why is there a torsional moment?
Section 7.4.3(2) offsets the resultant force horizontally from the centre of the board by a fraction of its width. That offset times the force gives a torsional moment at the base, which the posts and their connections must carry in either sense.
Does the force coefficient include end or corner reductions?
No. The signboard force coefficient carries no end-effect, corner or surface roughness reductions.
Are the results characteristic or design values?
Characteristic. Apply the partial factor for wind from EN 1990 for the ultimate limit state.
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