[TowerTalk] Concrete anchor

Sat Aug 15 03:50:13 EDT 2015

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

Ray,
N6VR 
----- Original Message -----
From: Rich Hallman - N7TR <rich at n7tr.com>
To: <K7LXC at aol.com><K7LXC at aol.com>
Cc: towertalk at contesting.com, kr5dx at yahoo.com
Sent: Fri, 14 Aug 2015 12:36:32 -0400 (EDT)
Subject: Re: [TowerTalk] Concrete anchor

I'm also in the middle of deciding on using an existing foundation or pouring a new one. What thickness plate would you go with for something like an hdx589? Buying the plate and having it drilled for the old foundation bolts.....then drilling holes for the new base bolts seems like a far easier option. Of course using structural bolts for the new base. 1 1/8 diameter f1445 grade 55 is what I'm looking at for the 589.

Thoughts?

Rich Hallman N7TR

On Aug 14, 2015, at 9:06 AM, K7LXC--- via TowerTalk <towertalk at contesting.com> wrote:

>> I have a 165ft rotating tower going up next Spring so will not be
> putting a larger tower on this base, but it does sound like I need to get a fab 
> shop to just go ahead and build me the base. No galvanizers locally so 
> paint will have to do. 
> 
>> I have a concrete base next to my shop that once had 89ft US Crankup
> Tower
>> on it. The tower is gone, and I acquired a 55ft US Tower that I want to
> bolt
>> to this base for use in my shop. The bolts that once held the bigger
> tower
>> is still there, but I plan to cut them off and install chemical anchors
> to
>> support the smaller bolt pattern. The other option was to fabricate an
>> adapter plate that would mate the 55ft tower T-base to the bigger bolt
>> pattern, but this sounds like much more work than simply drilling into
> the
>> concrete and installing new anchors.
>> 
>> I never used chemical anchors for this purpose and would appreciate any
>> suggestions on size, and where I can source them. The rebar pattern for
> the
>> bigger tower is much wider than the bolt pattern for the smaller tower,
> so I
>> there is little chance for me to hit rebar when I drill. (I suspect I
> will
>> need a BIG drill).
> 
> I assume that the big tower is a Rohn of some ilk. Adapting the base 
> for the new tower is pretty simple - and you don't need anything fabricated.
> 
> There are a couple of tower base options: 1) flat plate for regular 
> bottom section and 2) pier pin. For 1) you can put the plate on the base and 
> use a rotary hammer with concrete coring bit to drill out the bolt holes. 
> I'm not sure what you mean by a chemical anchor but in this case you'd use 
> some industrial epoxy to anchor the bolts to the concrete. The same with the 
> pier pin. 
> 
> Either option works although different folks prefer one over the 
> other. 
> 
> Cheers & GL,
> Steve K7LXC
> TOWER TECH 
> _______________________________________________
> 
> 
> 
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-- 
Ray,
N6VR