Jim,
I'd have to agree with you on the chemical over expansion anchors. I also
agree that it has probably been the engineers I have worked with.
Again, I remain a skeptic and if I was doing it, would probably prefer the
full caged rebar reinforced method. But that is probably due to my
"training" by the old school engineers.
Michael Wood
KE7ENC
-----Original Message-----
From: Jim Lux [mailto:jimlux@earthlink.net]
Sent: Friday, February 03, 2006 10:14 AM
To: AA6DX - Mark; Thin Air Communications; towertalk@contesting.com
Subject: Re: [TowerTalk] Epoxied bolts
At 08:55 AM 2/3/2006, AA6DX - Mark wrote:
>Michael ..So far, your conclusion does not mesh with what I have read at
>various sites, and in the past on this reflector..... But then, the
>companies are selling their glue ....
>but but but ... to engineer types, so... must be truthful?
>Hmmm ... watching this thread, as I have a back porch that is going to be a
>base for a crank-up --- Mark, AA6DX
>----- Original Message -----
>From: "Thin Air Communications" <thinair@thinair.cc>
>To: <towertalk@contesting.com>
>Sent: Thursday, February 02, 2006 9:45 AM
>Subject: Re: [TowerTalk] Epoxied bolts
>
>
>I am not an engineer nor do I pay one on TV. But the use of epoxied bolts
>from my experience drafting structural plans is limited to objects in sheer
>and never in tension. Meaning that yes, the epoxied bolt is no where near
as
>strong and solid as a "J" or "L" or caged bolt in tension.
The restriction of application to shear loads might also just be the
engineer's preference, or a response to some other set of
requirements. Chemical anchors are newer than embedded bolts, so there's
inevitably a transition period.
>The whole
>reasoning behind a "J" or "L" is so the bolt has something to grab on to.
It
>is possible to break the epoxy connection and lift the bolt from the hole.
In properly installed chemical anchors, the bolt will fail in tension
before the adhesive fails. See Hank Lomberg's post from a couple days ago
on this (since he IS an engineer who deals with this)
> I
>would refrain from epoxying bolts used in tension but would also rely on an
>engineer to evaluate the application.
And there's the key... in matters structural, where failure has high
consequences, get someone who really knows to evaluate YOUR particular
situation.
I philosophically "like" chemical anchors, particularly over long time
spans, compared to other "drill a hole and install bolt" approaches
(expansion bolts). Expansion bolts can crush or deform the sides of the
hole, and have potential problems with temperature cycling gradually
loosening them. (Although, properly installed, they should last forever, so
it's one of those gut feel things). Chemical anchors have a molecular bond
with the rock or concrete (although, I admit, there's a workmanship issue:
you can screw up the mixing and application of the adhesive)
I've literally hung my life from both kinds (as rock climbing anchors), and
I'd have to say, I have a lot more confidence in the chemical anchor than
the expansion bolt. Never had a chemical anchor pull out or fail, and I
have had expansion bolts (old, "manky" ones, I grant you) fail.
Jim..W6RMK
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