Wind Load Calculator: Design Wind Speed, Pressure and Force on a Wall or Sign (AS/NZS 1170.2)
Work out the wind pressure and the force on a wall, a sign or a surface once you have the speeds and coefficients from the wind standard.
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How this calculator works
Enter the regional design wind speed and the direction, terrain and height, shielding and topographic multipliers from AS/NZS 1170.2, then the pressure coefficient and the dynamic factor.
The calculator finds the design wind speed, the dynamic pressure 0.6 V squared, the design pressure on the surface, and the total force on the area you give.
With the height of the centre of the force it also finds the overturning moment at the base, for sizing a footing or a post.
Formulas used
- V_{des} = V_R M_d M_{z,cat} M_s M_t
- q = 0.6\,V_{des}^2\times10^{-3}\ \mathrm{kPa}
- p = q\,C_{fig}\,C_{dyn}
- F = pA,\quad M = F h
Worked example
With the default numbers in the calculator above:
- Design wind speed at the surface: 45.00 m/s (162.00 km/h)
- Dynamic (free stream) pressure: 1.22 kPa (the factor 0.6 is half the air density of 1.2 kg/m3)
- Design pressure on the surface (a negative value is suction, pulling away from the surface): 0.97 kPa (972.00 Pa)
- Total force on the surface: 19.44 kN (1981.65 kg-force)
- Overturning moment at the base (the force acting at the height you gave): 116.64 kN m
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
Why 0.6 V squared?
It is one half of the density of air, 1.2 kg per cubic metre, times the speed squared. With the speed in metres a second, the result is in pascals, so the factor 10 to the minus 3 gives kilopascals.
What does a negative pressure coefficient mean?
Suction: the wind pulls the surface away. Roofs, leeward walls and side walls are in suction.
Where do I get the multipliers?
From AS/NZS 1170.2, which gives the regional speeds for each region and return period and the tables for the terrain, height, shielding and topography.
Is this enough for a structural design?
No. It does the arithmetic. A structure needs an engineer to select the coefficients, the combinations and the load path.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: AS/NZS 1170.2 Structural design actions: Wind actions; AS 4055 Wind loads for housing.
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