[TowerTalk] Windload at 90 mph (was: Plumbing a tower)

[Jim Lux]

W7CE wrote:
>> One could look at the off-vertical situation by considering that
>> installing it non vertical puts a static side load on the whole thing.
>> The load would be sin(theta)*weight.  Say the whole thing weighs 1000
>> pounds (I don't know if this is plausible.. it's just easy to calculate)
>> and you're 2 degrees off vertical (about 3.5 feet in 100).  The side
>> load is about 35 pounds (distributed along the whole thing).  That's
>> pretty small compared to the wind load (90 mi/hr = about 20 lb/sq ft,
>> and you know the tower has a lot more than 10 square feet of cross
>> sectional area)
>>
> 
> Is 20 lb/sq ft correct for 90 mi/hr winds?  I've run several of the 
> published formulas in the past and seen other references that would 
> indicated that 36 lb/sq ft is a good number to use at 90 mph.  I realize 
> that it is dependent on height above ground and other factors.  Have I 
> miscalculated or am I in the right ballpark?
> 

36 lb/sf is more like 120 mi/hr...

lb/sqft = Vmph^2/391 is the equation.
8100/391 -> 8000/400 -> 20 approx

391 is the half the density of air in weird units  (F = 1/2 * A * rho * V^2)