[TowerTalk] Tower ACCIDENT

[Jim Lux]

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.