Windforce

[gerkin]

For a constant wind speed does wind loading increase for an increase in specific humidity and pressure ?

[gen2]

The wind load will depend upon the density of the air.

Increased atmospheric pressure will increase the density of the air and therefore the wind loading.

Increased humidity however reduces the density of the air and will therefore reduce the wind loading.

[Clanad]

While gen2 is certainly correct, another important consideration is the temperature of the air.  Cold air is more dense than warm air, so for any given wind speed, the actual force changes with the temperature, along with the considerations for humidity and air pressure...

[Dacetine]

Following gen2's answer, I do not understand why increasing humidity results in decreased air density? Am I being stupid?

[gen2]

Dacetine (and any others), It is all to do with Avogadro.

If the temperature and pressure remain constant, a fixed volume of air will contain the same number of molecules, regardless of the gas. At Standard Temperature and Pressure (STP) 22.4 litres of gas will contain 2g of Hydrogen, or 28g of Nitrogen, or 32g of Oxygen, or 18g of water vapour.  Air being mostly nitrogen + oxygen will weigh around 29g per 22.4 litres.  As water vapor enters the air, it does not add to the mass, it displaces some of the heavier N2 and O2 molecules and replaces them with the lighter water molecules (H2O).  The density of air therefore goes down as the air gets more humid.

Look up 'Avogadro's number' and '22.4 litres' in google for more details