Wind Load on Basement Levels?

[psychedomination]

Hi there,

I am working on a project, where the architect has included a basement level for a residential renovation. This is a 3-storey structure (when you include the basement level)

- Basement level
- Ground floor level
- 1st floor level

Total building height from basement level to roof of 1st floor level is ~35'.
I'm in a hurricane-prone region. In the basement level there is an open courtyard with trees etc (about 200ft2 of open space) about 11' below grade level.

How should I go about calculating the windload at the basement level. Would it be the same calculation approach as if the building was built from grade level up? Or is there a provision in ASCE to reduce the wind load for below-grade open spaces?

Any assistance would be greatly appreciated.

 

[ANE91]

Wind is 0 at surface of the earth.

ASCE says use some minimum pressure for the first 15ft above grade. Power law takes over thereafter. Screenshot below from ASCE 7 demonstrates this.



Wind doesn’t know that it’s below the downwind grade until it reaches said grade and speeds up. You account for this speedup with Kzt.

You might want to read about sectoral analysis in the Commentary. It’ll give you an idea of what ASCE is doing. The equations will make more sense.