[TowerTalk] Concrete anchor

Sat Aug 15 22:28:04 EDT 2015

Normally, I see substantial  locking nuts used on the back side of steel 
plates

73

Roger (K8RI)


On 8/15/2015 12:24 PM, Ray Benny wrote:
> John,
>
> I wanted all the strength I could get using the adapter plates. The original tower base plate had only 6 - 1" mounting bolts, while the new tower plate has 12. Besides, I did not know mathematically how to figure what thickness of steel plate I would need. 1" sure seemed thick enough to me.
>
> With the additional six thread stock bolts coming out of the concrete and going through the adapter plates and tower base, I am confident that the tower will stay in place.
>
> Ray,
> N6VR
>
>    
> ----- Original Message -----
> From: john at kk9a.com
> To: towertalk at contesting.com
> Sent: Sat, 15 Aug 2015 10:28:38 -0400 (EDT)
> Subject: Re: [TowerTalk] Concrete anchor
>
> Why wouldn't you just tap 1-8 holes in the adaptor plate, bolt this plate to
> the concrete using the existing bolts and then bolt the new tower base
> directly to the adaptor?
>
> John KK9A
>
> To:	Rich Hallman - N7TR <rich at n7tr.com>
> Subject:	Re: [TowerTalk] Concrete anchor
> From:	Ray Benny <rayn6vr at cableone.net>
> Date:	Sat, 15 Aug 2015 03:50:13 -0400 (EDT)
> List-post:	<towertalk at contesting.com">mailto:towertalk at contesting.com>
> Rich,
>
> I replaced a medium size 71ft tower with a heavy duty 71ft tower several
> years
> ago. None of the existing six 1" bolts matched with the new tower base
> plate,
> 12 bolt holes. In a sense, I made adapter plates for the old and new tower
> base
> bolts
>
> What I did was purchase two 1" thick  by 10" flat steel plates (one was 30",
>
> the other 36" long) and scribed the existing 6 bolts, and the new tower base
>
> bolt pattern onto these plates. I then had the steel company drill 1 1/8"
> holes
> at the center of the scribe marks. Now the 1" steel plates fit over the
> existing concrete bolts, and allows the new tower base plate to set on top
> with
> matching holes. The existing 6 bolts were then bolted onto the 2 plates with
>
> nuts between them and the concrete. On all but six of the new base plate
> bolt
> holes I used short bolts, nuts and bolted the plates and new tower base
> plate
> to the concrete. The remaining 6 holes would have new bolts (hardened
> threaded
> stock) epoxied into the existing concrete base.
>
> Next, I was able to find a local guy who specializes in concrete boring. I
> had
> him bore 6 - 1 1/8" holes into the concrete base to 20" depth, aligned with
> the
> steel plates and new tower base holes. I used the steel plates as templates.
> I
> then bought 1" hardened threaded rod stock, cut to 24" lengths at the steel
> shop using a special blade (remember its high grade steel) and used the
> epoxy
> recommended by the steel company to epoxy in the new 1" thread stock. Since
> the
> 1" plate holes and concrete holes were cut to 1 1/8", there is not much room
>
> for miss-aligning. Make sure the thread stock goes thru everything and will
> seat at the bottom of the hole. Not all mine came out properly aligned so I
> had
> to use a rotary rasp and elongate a few of the holes on the steel plates.
>
> Mixing and pouring the epoxy is a messy job. The epoxy comes in two separate
>
> tubes and you must use a special mixing applicator device that mixes the
> epoxy
> as it is injected into the holes. Luckily, my local concrete guy had one I
> could borrow. Putting the right amount of epoxy into the hole is a hit and
> miss. You want just enough in for it to ooze out of the hole once the thread
>
> stock is pushed in all the way down, but not too much extra. The epoxy is
> not
> cheap. The first time I tried, the epoxy did not come out of the hole, so I
> had
> to pull the threaded stock and add more epoxy. This makes a real mess, the
> epoxy sticks to everything! the epoxy hardens in about 10 minutes and so the
>
> thread stock must be set right the first time! I suggest you use a small
> wooden
> dowel as a depth gauge once you determine the right amount epoxy that is
> needed
> per hole.
>
> According to the manufactures specs, maximum pull out strength is obtained
> at
> just 20" depth into the concrete for a 1" threaded rod stock in a 1 1/8"
> concrete bored hole. You must go to the specs and see what size hole to bore
>
> and to what depth for your base bolts/threaded stock size.You cannot just
> bore
> any size hole, fill it with epoxy and shove in the thread stock.
>   I feel totally comfortable with what I did. And according to the specs, the
>
> bolt will shear/break before it would pull out of its hole!
> I can provide photos of the 1" plates, the concrete boring, and the final
> completed job.
>
> With the right size threaded stock and correct hole size bored and depth,
> epoxy
> should work on any concrete tower base, as long a the base meets the
> manufacturers size and rebar requirement.
>
> Good luck,
>
> Ray,
> N6VR
>
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-- 

73

Roger (K8RI)


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