To: "INTERNET:seaint(--nospam--at)seaint.org" <seaint(--nospam--at)seaint.org>
Subject: Re: ACI 355.2
From: Peter Higgins <76573.2107(--nospam--at)compuserve.com>
Date: Wed, 21 Mar 2001 17:15:15 -0500
Re Mark Gilligans posting (omitted here for brevity).
The more I dig into it, the more I am surprised at this thing.
We have here a classic red herring. Concrete does crack. All the time. The
test procedures are in real concrete.
The proposed procedure is not representative of reality (how many of us
install anchors into a strip 2-3' wide, with a known crack all the way
across the width?). Maybe if I did anchors exclusively in sidewalks, I'd
have some sort of a problem, but not in a building sized chunk of concrete.
I personally have installed dozens of anchors into construction and full
cold joints in a slab and then pulled them to ensure they perform. I have
yet to find any problems. Why? I don't know, but there aren't any, and
that's the bottom line. One shouldn't put theory ahead of Mother Nature's
teaching. Yeah, the equations look impressive. However, when I substitute
into them, I get an answer which predicts failure at a small (less than 5%)
fraction of what these anchors were known to pull. This isn't safety factor
territory, it's plain wrong. When the theory doesn't fit reality, one
doesn't continue to insist on the theory. You go back and find out what's
wrong with the theory.
Millions of these things are installed every year. If cracking were a
problem, you would not even be able to set these anchors (the proposed
procedure requires that the pretension be present during installation. It
is only relaxed AFTER the anchor is installed. If they didn't do this, you
would never even get an expansion anchor to so much as set, let alone
develop significant torque).
The procedure also deliberately distorts the hole after drilling, which
most certainly isn't representative of reality.
With all due respect to the list, I have yet to see documented, published
problems with expansion anchors, let alone the sort of evidence required to
outlaw them completely. Anecdoteal stories can hit the trash can as far as
I'm concerned. It takes cold hard data to base a decision, not vaguely
remembered stories related second to third hand. If the data are out there,
where are they? Show me, and I'll be the first to change my mind and admit
the error of my ways. The first guy (person) to show it to me will also get
a free dinner at the restaurant of their choice.
Peter S. Higgins, SE