Wind Loading - Kzt

[Skazak]

I am working up the design loads for a building on top of a hill in the middle of a plain.

In working up my Kzt value per ASCE 7-05 Fig 6-4, what exactly is the 'z' value used to calculate K3?

ASCE calls out z to be the "height above local ground level".

With my building at the top of the hill, will this result in z = H?


Followup question: If this is the case here is my problem. My hill is steep so that H/Lh > 0.5.

According to note #2, this means that I am to substitute 2H for Lh for my evaluation of K3.

This being the case, my K3 factor will be z/Lh => H/2H => 1/2

In other words, because my hill is steep, my K3 term can never get bigger then 0.14.

Is this correct?

Thanks

 

[chichuck]

Skazak,

z is the height above the base of your building. (Local ground level is the base of your building.) Thus, K3 varies from bottom of bldg to top. For your case, with the steep hill, you calculate z/2H for various heights on your building, then use the values in the table, with linear interpolation between the values to obtain K3 for any or all locations above your bldg base. That value will get bigger than 0.14 for the lower reaches of your building height, and will get down to 0 at heights > 1.50* (2H) = 3.0*H.

Also from Note 2, use x/2H instead of x/Lh to determine K2.

Calculate Kzt according to the formulas in the code.

Hope this helps.

regards,

chichuck

 

[miecz]

chickuuck-

Are you sure about that? The sketch that accompanies figure 6-4 doesn't measure z from the base of the building.