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[TowerTalk] tower installation HG52SS

To: <>
Subject: [TowerTalk] tower installation HG52SS
From: "Wilson Lamb" <>
Reply-to: Wilson Lamb <>, "Tower and HF antenna construction topics." <>
Date: Fri, 12 Feb 2010 12:25:21 -0500
List-post: <">>
If you really have rock, why are you digging?
The big concrete bases above ground are impressive, but if not securely 
attached to rock, they will easily turn over!
There's no need for all that rebar framing, except in a big hunk of 
Why not just use some of the techniques shown to tie down your tower base to 
the rock?
If you don't think the base provides enough holes, weld it to a steel plate 
and tie that down with as many rockbolts as you need.

I just used some 1" stainless expansion anchors from Fastenal to tie down 
some large objects.  They are well made and Fastenal can provide ratings. 
They provide a psychologically reassuring grip at the bottom of the hole 
that you may like, but I have no idea how they compare to grouting.  For 
sure, grouting depends upon adequate roughness of the pins, like the rebar 
surface, and the sides of the hole.

The modern SDS drills are amazing.  Harbor freight even has a cheap one that 
will surely last long enough to finish your project.  Your greatest hazard 
is horizontal separations of the rock, so your hole has value to help you 
asses the quality of the rock!

Since you have the hole started, how about setting some long anchors in the 
pattern of your tower base holes with epoxy, welding them to a rebar cage 
and then pouring concrete to level your hole at the original ground level?

It's sure worth getting the expected overturning moment from the tower 
company and checking the anchor ratings against it, which is pretty easy.

It's hard to get comfortable with all this grout/epoxy technology, but done 
right it's good.  Remember all the concrete ceiling slabs held up in the Big 
Dif in Boston?  And the one that fell down because of improper epoxy use?

Here's a 3/4" drop in anchor.  You can screw threaded rod of any length into 
it after it's expanded by driving in a bolt to expand the lower part..

Adhesives for anchoring

Here's a manufacturer's catalog showing drop ins.  They show relatively 
shallow setting, so I doubt if the numbers are anywhere near the ultimate 
capacity of the anchor.  No doubt they would advise you about rock 

Anchor performance with epoxy.  Failure modes explained and example 

Wow, this is fun stuff.  I think I'll put up a tower this year.


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