Commercial towers have no fancy thrust bearing. It's usually just a very
heavy but small diameter plate that is just large enough to accept the
angled in tower legs, which are welded to the plate in the most amazing
mass of welding you ever saw. And this small plate just sits on a larger
plate on the concrete base centered by the pier pin.
-Steve K8LX
On 5/11/2011 10:45 AM, Dick Green WC1M wrote:
> Regarding the pier pin base, I agree that in theory it's the way to go, and
> that's what I have on my 110' Rohn 55. However, I've often wondered if the
> Rohn flat-plate pier pin base used by most hams who install pier pin bases
> really does what a pier pin base is supposed to do, namely provide some
> "give" in response to torquing forces on the tower. Seems to me that the
> friction between the base plate and concrete is substantial, especially
> given the weight of the tower/antennas/rotors/cables and the downward force
> of the guys. Does the plate really move? How much wind would it take to move
> it? I've never detected any evidence that mine has moved. Commercial pier
> pin bases are tapered and, if I'm not mistaken, the pin fits into a bearing
> of some sort (probably a thrust bearing) attached to the concrete.
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