>
> I just looked on line and I see no reference to that. On 45G they show and
> talk about the gravel in the bottom of the hole, tower legs placed on the
> gravel so they drain, etc etc. But then, maybe I'm looking at the wrong
> page......... OR maybe pier pin for really tall towers. My 40', 45G, is
> "in the ground". Now if I was lucky/brave enough for 80' or more, I would
> probably go pier pin. As always, YMMV.
>
As far as I can tell, all of the bases that show the legs placed on gravel
are for free-standing and bracketed towers. The guyed towers all specify
bases CB1 to CB3 which are all pier-pin bases.
Over the years most ham installations have ignored Rohn's instructions and
buried the base in concrete. Commercial installations, which certainly
required an engineer's stamp, have primarily used pier-pins. There's a
reason. The pier-pin bases are less likely to fail due to twisting and
bending at the base. K7NV has done a study of this and posted the results.
It makes interesting reading.
http://k7nv.com/notebook/towerstudy/towerstudy1.html
You'll note that the tower that failed in this study did so at the base
section buried in concrete, not the upper sections. When the base was
replaced with a base that can move (i.e., a pier pin), the tower survived
with much large safety margins.
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