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RE:"Epoxy?/Chemical? Anchors"

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Thought I would respond to a couple of comments that have appeared about
"epoxy anchors." 

First, "epoxy anchors" seems to be the commonly used generic term, when, in
fact, epoxy is only one of several chemical anchor types available in the
market: epoxy (with many variations and formulations to take advantage of
temperature ranges, load capacities, etc.), polyester, vinyl ester (also
known as epoxy acrylate, but somewhat different from pure epoxies),
acrylics, methacrylates, hybrids that also include cement, etc. Each of
these have advantages and disadvantages that the specifier should
understand. The more generic term should be "chemical anchors."  We also
find the terms adhesive anchors, adhesive-bonded anchors and bonded anchors
in use. Never-the-less, epoxy should only refer to one type of "chemical
anchor."

Over the past weekend, someone provided the comment that "polyesters reacted
with the alkalinity of the concrete to form a compound of water soluble soap
and the anchors would literally slip out of the drilled holes."  Don't
believe this. It just isn't true.  Polyesters are still available in the
market and function well.  The issue is that under high loading (50 to 75 %
of ultimate capacity) and in a wet condition some of the polyester molecular
chains are attacked by the alkalinity in the concrete (hydrolysis) and
break.  There can be a reduction of 25 to 30 percent in ultimate capacity.
Under ASD, generally a global safety factor of 4 is used.  With a reduction
of 25 to 30 %, there is still a safety factor of about 3 which is enough to
provide sufficient resistance in the anchorage.

The second comment (see below) that "epoxies [are] no good in fire" because
of the finding in an ICBO ES evaluation report, is reading too much into the
report.  First, ICBO ES Acceptance Criteria for Adhesive Anchors in Concrete
and Masonry Elements AC58 does not contain specific criteria for evaluating
the performance of chemical/adhesive anchors under fire conditions. Thus,
manufacturers are at a loss as to what data and testing to submit for
evaluation by ICBO ES. The finding in the evaluation report means that the
anchor system has not been evaluated for fire conditions, therefore ICBO ES
cannot state in the evaluation report that the anchors are acceptable for
use in fire resistive construction. This is a far cry from the idea that the
anchors are no good in fires.  

At least two manufacturers have performed fire tests on both mechanical and
chemical anchors.  One obvious finding of the tests is that concrete is a
pretty good heat insulator.  The chemicals don't just melt and the anchors
fall out.  The anchor is usually protected by a base plate so that oxygen is
not readily supplied to the chemical.  They also don't just melt.  Some
soften, but still retain significant resistance. The anchorage has to reach
significant temperatures within the concrete (to most of the embedment depth
of the anchor) to substantially affect the capacity of the chemical bond.
Meanwhile, the steel of the anchor rod and nut are being affected more
severely, since they are directly in the fire.  Something to think about.

Richard E. Wollmershauser, P.E.
Director Technical Services, Hilti, Inc.
Tulsa, Oklahoma
Tel: (918) 252-6571
Fax: (918) 252-6347
E-mail: wollric(--nospam--at)us.hilti.com


-----Original Message-----
From: Gerard Madden [mailto:GMadden(--nospam--at)mplusl.com]
Sent: Thursday, July 26, 2001 11:36 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: No ICBO - Satisfy plan checker


Thanks to everyone for the replies...

I guess I just find it odd that performance based design can be readily
accepted by building departments but a drive pin and the actuator need ICBO
reports or forget about it.

Scott, You have valid points and those are all circumstances where the ICBO
report has told you the weakness in the system (i.e. epoxy no good in fire
etc...) believe me, in the few jobs I have checked I have seen some
horrendous mistakes ( i.e. no wall anchorage in brand new designs for CMU
buildings, no collectors or chords - the basic load path stuff) However,
when it is simply a rat race between different manufacturers to get approval
from ICBO, which takes some time, the engineering behind these items are
sound, it becomes frustrating sorting through who's up to date from job to
job.

For example, the strongwall vs hardy panel/frame which has come up. Simpson
publishes strongwall for raised floor and 2nd floor applications, however,
they do not have ICBO approval for this application. Hardy has a similar
product with the very approvals the strongwall is lacking. Simpson will
eventually get the approval no doubt, but they were simply the 2nd fastest
to address the issue, thus making their product inappropriate for a
kindergarten building  fire country until ICBO gets around to evaluating
their test data. I have no problem with this, except that when
manufacturer's publish these items in their brochures with new approval
claims, then they don't have a current ES report, it makes it really
annoying trying to sort all this stuff out.

I guess what I am trying to say is that it ain't easy for anybody except the
building official who can just say yeah or nay on their gut feeling. Yet, If
I do a performance based design retrofit, ship my design around to a couple
of firms with all PhD's and SEAOC big shots who believe in PBD, no problemo.

Anyway, thanks for the responses ... they have been helpful-as always.
-gerard
SF, CA


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