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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