[TowerTalk] 130mph Rohn 25G

[Hank Lonberg]

I am really curious as to how this works.

When I calculate the bending moment for a 40 foot section of 25G with a
bracket at 8' up using TIA/EIA-222-F specifications for 130 mph design wind
velocity, I get a moment of 15,872 ft-lbs at the bracket. This is over twice
the allowable as specified by Rohn. This for the tower section alone with no
antenna loading.

When I use 80 mph design wind velocity I get 6,042 ft-lbs which is just less
than the 6,720 ft-lbs of allowable moment as specified by Rohn for 25G.
Again this is without any antenna loading. This would equate to having about
1 sf of allowable antenna capacity at the top.

Can some one explain their calculations to me as it appears that I am doing
something incorrectly!

Regards

Lonberg Design Group, Ltd.

Hank Lonberg, P.E.,S.E. / KR7X
President