Well, I Googled it, finally.
Did you realize it's rated for 50 mi/hr, with max load, 9.5 SF?
I'm betting a big triband quad will get close to that, as will a large
The T-11 LP is 11.5, I think.
It sounds like you should have some guys no matter what!
To the point of design:
I don't think gluing the concrete down is realistic.
The drawing shows that the three rebar legs are capable of supportiing the
tower at full load, so why isn't the drill and grout I suggested a good
answer, assuming you verify the performance of the grout/anchors.
Getting the working tensile rating of the rebar would be a good first step.
Is it 1" bar??
Depending on the length of the base, it looks to me like cutting the plates
off and weldiing them to the other end of the bars and then sinking the long
ends of the bars in the rock would work out about right. Or cut the lower
braces off and move them higher. Then you could use the plates as they are.
You wouldn't have expansion anchors, of course, just the epoxy, which may be
The next improvement would be to get threaded rod with the same tensile
rating as the rebar, which should be easy, and setting it with expansion
anchors AND epoxy...belts and suspenders.
You could weld on a few braces like the original, if you like them, but they
are there to reinforce the concrete and take tensile load if the rebar slips
in the concrete. If your anchored legs work, the braces will see no load!
The concrete glob should have bars around its perimeter and some crossways,
just to keep it from falling apart.
I don't see any reason for the concrete to be above the original ground
level, or to be square. You could move over and have no concrete at all,
but since you have the hole it will be good to use it because it puts your
anchors deeper into the rock, where it's probably stronger.
What could be cheaper than the above? I'm betting three anchors and some
threaded rod, galvanized, would be under $100. The epoxy I used on a job
here was brutally expensive, but it doesn't take much.
The C-6 epoxy develops 48,000 pounds tensile in a 1"X9" hole, but I'm not
sure what surface roughness is required on the rod.
----- Original Message -----
From: "Michael Goins" <firstname.lastname@example.org>
To: "Wilson Lamb" <email@example.com>; "Tower and HF antenna
construction topics." <firstname.lastname@example.org>
Sent: Saturday, February 13, 2010 6:37 PM
Subject: Re: [TowerTalk] TowerTalk Digest, Vol 86, Issue 53
Okay, just for clarity, I've had a ticket for over 30 years and this
isn't the first tower I've ever put up or helped put up or been up.
And it is also important to me to do it right, but I am not looking to
do thousands in the base and do this in a realistic, practical manner.
The circumstances are different here because of the rock, and that's
why I asked this knowledgeable group.
We were in the Houston area in the past, which is mostly gumbo soil.
Here it is rock, on the side of a hill up 1800 feet, and the hole is
in solid rock - not shale, not limestone, a boulder. A solid rock
shelf. The specified hole, by the manufacturer, is 42" X 42" X 5.5
feet. We are now at about 3.5 feet, making the hole a couple of feet
shallow at the moment. It is SOLID rock, nothing more, nothing less -
no cracks, no splits, solid.
It is going to be where we will stay, likely, forever. I am a quad and
homebrew antenna guy, so it will never have multi-stacks or whatever.
A quad now, a monobander (if that) in the future. A tied-in pad at the
top which is say, 5X5 feet would have to be pushed into the soil from
the opposite side to move, and that will not happen as the area is
rock and less than an inch under the soil. That is why I thought a top
pad might help, even though I know it needs to be deeper or at least
epoxied into the stone shelf. I have to have a squared up pad at the
top anyway, so 4-5 feet square would accomplish both tasks.
The tower base doesn't have holes - it is a HG52SS and I have the
factory heavy-duty rebar base with the ears on it that double bolt to
the tower legs. The base sits in the hole, is cross-braced, and
concretes in with only the ear part sticking out to attach the tower
I may cut the lowest brace off the factory base and drill 3 holes for
the three base legs to drop into and then epoxy them in with the
special rock epoxy. The factory base will then lack the lowest brace,
but I'd add one up higher that would be in the concrete pour and the
three 1" rebar factory legs would be epoxied in about 18" into the
Still looking for ideas so this is a right as I can make it, and, for
the record, I won't lower the tower all the time, but will when I know
there is weather coming or when away for any period of time. The rest
of the time it will have a 2-el quad on it.
Pipe Creek, Texas
Fast cars, slow boats, big dogs, and summers off to write
On Sat, Feb 13, 2010 at 3:44 PM, Wilson Lamb <email@example.com> wrote:
> In answer to Kipton, below.
> The slug of concrete sitting in the rock bowl can't be expected to hold
> anything, unless the sides of the hole are near vertical. The point of the
> rods drilled into the rock is to take all the load in tension, like the
> nails someone mentioned and as they will do in all the base designs with
> concrete. He would have been as well off to just drill into the top of the
> The unknown, of course, is the quality of the rock, which he can determine
> with deeper borings and horizontal excavation to see if there are cracks
> coming to the surface. In other words, he doesn't want to bore into a
> separated block of rock that can move.
> Do not depend upon letting the tower down in strong winds! Sure, you can
> it sometimes, but what about the time you're away, or asleep?
> Deep expansion anchors, with their threaded rods grouted or epoxied, seem
> good way to go.
> It would be a good idea to have an engineer sign off on it though, at
> under the assumption that the rock is good. He would not have to come out
> to do it.
> A good first cut would be to use threaded rod as large as will go through
> the holes in the tower base and set the anchors to develop the working
> strength of the rod. No design can do better than that, if you use the
> right rod material.
> If we had a drawing of the base and the expected moment, we could actually
> talk about the loads with some accuracy.
> Of course one set of "insurance" guywires at the top would make things
> really nice!
> Not to hijack the thread or anything, but I have been following this
> discussion, and the comments suggest drilling holes into the rock base
> and attaching the rebar into the holes with something like epoxy. That I
> can understand.
> He is 3 1/2 feet down. Would it be a good idea to also drill
> horizontally into the sides and epoxy rebar into the sides also? It
> seems to me (uneducated in his stuff) that would have a big effect
> preventing the forces from moving the hunk of concrete. With all the
> rebar cemented vertically you are depending on the strength of the epoxy
> (plus the weight of the concrete) to prevent the tower from falling
> over. But if you also went in the sides, then you would also have to
> shear the rebar to get it to tip over.
> Of course you would have to be low so you do not have a chance of
> breaking out the top of the stone. Am I thinking correctly or is there
> something I am missing?
> Kipton Moravec AE5IB .- . ..... .. -...
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