terrain roughness factor Kr

[eriksasha]

I'm trying to set up an excel spreadsheet for BS8100 concerning wind loading on masts but have not been able to find an equation for determioning Kr (terrain roughness factor).

Does anyone out their know the equation?

 

[Bagman2524]

ASCE-07 has a topographical factor Kzt which is equal to
(1 + K1*K2*K3)^2 (i.e square of everything in paranthesis).

K1 is determined from a table that depends on exposure category

K2 is (1 - !x!/uLh)

K3 is e^(-yz/Lh)