[TowerTalk] Concrete anchor

[john at kk9a.com]

That makes sense.  The original poster NJ0F was changing to a smaller tower where an adaptor plate with no extra bolts should be adequate (if properly designed). 

John KK9A


-----Original Message-----
From: Ray Benny [mailto:rayn6vr at cableone.net] 
Sent: Saturday, August 15, 2015 12:25 PM
To: john at kk9a.com
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Concrete anchor

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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Ray,
N6VR