Application of wind loads

[Br_Engr]

Ok. Flaunting my ignorance for all to see here.

Reviewing wind loads, and it DOES look something like this (Thank you @NikR_PE):



and have a question about the application of the design wind pressures.

Examples show that the design wind pressure on the windward wall is a uniform pressure for the first 15' (q15) and then varies linearly up to the wind pressure at the mean roof height (qh).

My question is: Where is it stipulated that a uniform pressure is applied for the first 15'? Is a code requirement or just convention? The design pressure figure from ASCE-7 shows the parabolic pressure distribution starting at 0 at ground level to qh, but also has a line representing (what I think to be) the uniform pressure component.



I was not able to find anything that explains the origins of this approach. I am not questioning this, just trying to understand where it comes from.

As always, thank you in advance for all of your help.

Br_Engr

 

[thedaywa1ker]

If you're asking how the bottom 15' is implemented in the wind provisions, its by the Kz factor that is the same from 0-15'

If you're asking why they do that...don't think I can point to anything in the code about it. Plain old simplicity and conservatism probably.

 

[Br_Engr]

Thank you. I understand how it is computed, just was not aware of the "why"