When you place a 45G concrete base plate with the pier pin centered over an
18"radius pier, two corners will overhang.
The plate hole is centered with the legs, not centered with the plate ;-))
That's the gotcha...
K4EAR
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Joe Subich, W4TV
Sent: Wednesday, October 26, 2011 4:10 PM
To: Richard Thorne
Cc: Towertalk
Subject: Re: [TowerTalk] Tower Base Round or Square?
I asked the same question of a well known Professional Engineer a couple of
years ago. His answer was quite simple and made a lot of sense ... the
round base can be used instead of a square one if the diameter of the round
base is the same as the *diagonal* measurement of the square base.
In your case, for a 2' 6" (30") square base the round equivalent would be
42" diameter *not* 36" as you propose. The reason has to due with projected
surface area - the area that resists overturning
- not volume (or weight) of the concrete.
73,
... Joe, W4TV
On 10/26/2011 1:28 PM, Richard Thorne wrote:
> I'm finally getting some dirt work done in the next day or two at my
> new place which will include holes/concrete for my 45g tower.
>
> I plan on using a pier pin install, so does it matter if the base is
> square or round? The rohn book calls for a 2' 6" square hole 4' deep
> (I'm designing the tower based on 90mhp winds with a height of 120').
> It would be easier to use a 36" auger to dig the hole. Since I'm
> going with a pier pin I don't see that there would be any twisting
> moments on the concrete base, it would only be there to hold the tower
> up. But I'm not an engineer, hence the question.
>
> Thanks
>
> Rich - N5ZC
>
>
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