At 05:27 PM 6/27/2007, jeremy-ca wrote:
>Rohn offers 3 mounts using flat steel plates. What I have done is use the
>idea of the self supporting mount, 25GSSB, which uses mounting holes in the
>4 corners. By drilling 3 holes and going from 5/8" to 3/4" bolts it
>increases the strength a bit. Probably not necessary, especially on short
>towers or light wind loads. The pier pin is not used on a bracketed tower.
Hmm.. by going to a larger bolt, assuming it's the same material,
you've increased the shear strength of the bolt by 20%, but decreased
the strength of the flange that's being bolted by some amount (I
don't have the drawing in front of me). Why not just use a stronger
5/8" bolt if you're worried about shear failure? You can get awfully
strong bolts (Titanium or very strong steel)
On a bracketed tower, you're going to see almost all shear loads,
because the bracket will act as a fulcrum. Even with a monster
antenna in a huge wind, you're probably only going to see a few
hundred pounds lateral force on the bolt. That's not a big
amount. The bolt load is probably dominated by the vertical down
force from the weight of the tower, unless the tower weight is
supported by the base.
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