Yes he does, and one which I've mentioned here in the past. I think that
the more important feature of a pier pin base is the tilt freedom to
keep the downward force on the legs equalized, rather than rotational
freedom, but that depends on the circumstances.
One relatively easy way to improve the system is to place a large nut or
washer(s) over the pier pin but under the base plate to raise the plate
off the concrete and to provide somewhat of a ball bearing to pivot on
(in all axis).
Except that the Rohn base plate isn't strong enough to do that (except
on a short tower maybe), so another, thicker plate should be inserted
under the standard base plate to give the necessary stiffness.
And I would also provide another plate under the nut to spread the force
over a larger section of concrete.
-Steve K8LX
On 5/11/2011 12:04 PM, Pete Smith wrote:
> I think Dick has a good point. I've always assumed that it would not
> move until the last 5 percent of wind loading, and maybe not even then,
> given the rise in downward forces. I think if I had it to do over
> again, I would put a sheet of Teflon or maybe even Lexan between the
> plate at the bottom of the lowest section and the concrete base, in the
> hope that it would promote rotation when really needed. I think that
> K7NV's study assumed a near-zero-friction pier pin base, and the Rohn
> version for these "little" towers certainly isn't.
> 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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