I completed a similar project last year (HDBX-48). I tried to document it on
my web site http://www.kk0sd.net . I did not spend a lot of time explaining
the steel I used, but I did what Rohn said and added vertical pieces of steel
(more rebar) to hold the two grids in place during the pour and clamped the
ground lines from the bolts to the cage. I figured the clamps would stay tight
burried in concrete. My advice to everyone is to make sure to rent the concrete
vibrator! It is a wonderful tool. 73,Joe kk0sd
> To: towertalk@contesting.com
> Date: Mon, 11 Jun 2012 16:31:32 +0000
> From: n0tt1@juno.com
> Subject: [TowerTalk] Concrete tower fountains plans...some questions
>
> Hi Gents,
>
> I'm planning to erect a new 68' self-supporting BX tower and I'm
> going over Rhon's specifications for the concrete foundation.
> (I have NO desire to deviate from those specs.)
>
> A few questions:
>
> 1. There's a grid of 3/8" rebar about 3" up from the bottom
> and is about 4ft square and flat. What's the best
> way to support that off the bottom of the hole while
> the concrete is being poured around it? And will
> the supports allow water to enter and corrode the rebar?
>
> 2. There's also a grid of 3/8" rebar about 3" below the
> TOP surface of the foundation. The rebar is placed at 12" centers.
> I'm *thinking* that the grid can be suspended from the wooden
> jig I'll build to hold the anchor bolts firmly in place while the
> concrete is being poured. From your experience, would
> that be the best/easiest way?
>
> 3. I've read/heard somewhere that rebar in concrete
> tower foundations should be connected/bonded to the tower
> ground system. Seems logical, but is that true?
>
> 4. The Rohn spec sheet shows the TOP of the fountation
> 6" above grade. Why the 6"?...to allow for "growth" of the
> soil around it? Why not, say 3" and dig the foundation
> hole a little deeper?
>
> 5. The 1-inch anchor bolts have a nut and washer above
> and below the U-brackets that support the tower. Is it
> customary to place some anti-sieze compound on the
> threads to easily allow minor adjustments due to any settling
> of the foundation...say in 5-10 years or so?
>
> 73 and thanks for your input,
>
> Charlie, N0TT
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