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RE: Anchoring in seismic zones

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As a participant in the drafting of seismic test method 2 in both ICBO ES
acceptance criteria, AC01 and AC58, I would like to provide some insight
into the ICBO ES testing that supports the approval for seismic loading in
evaluation reports. The test is a pass/fail test at load levels that are
approximately twice the "allowable load" published for the anchor. The test
is a test of the anchor, not the concrete.  The response below, which has
appeared previously, is based on an assumption that if the laboratory
concrete block does not crack from the loads applied to the anchor during
the laboratory testing, then the concrete in a structure will not crack in
service.  

Seismic loads result from response of the structure to ground movement,
which may cause cracking of the concrete in tension zones, with or without
anchors. One cannot say that the seismic testing of anchors in uncracked
concrete laboratory blocks proves that the concrete in structures will not
crack during seismic events. The issue remains that concrete in structures
may crack under seismic loading, and the ICBO ES evaluation reports, while
"approving" anchors for use under seismic loading, still restrict anchors to
uncracked concrete. 

Finally, the suggestion that the epoxy may serve to strengthen the concrete
and prevent cracks from intersecting the anchor location is not borne out in
laboratory testing (see Cannon, R.W. ACI Structural Journal, Nov.-Dec. 1981
and Burdette, E.G. et al. ACI Structural Journal Mar.-Apr. 1985). The epoxy
around the bolt, no matter how high the compressive or tensile strength, may
not act to deflect crack propagation any more than the presence of aggregate
in the concrete can confine cracks to the cement paste. Cracks run either
through the aggregate or around it, but not away from it.

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: COEngineer(--nospam--at)aol.com [mailto:COEngineer(--nospam--at)aol.com]
Sent: Wednesday, May 16, 2001 12:14 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Anchoring in seismic zones


Select anchors that have passed seismic testing.  ICBO ES seismic testing is

done in unreinforced concrete.  If the concrete is going to crack at the 
anchor location due to the applied seismic load, this will happen during 
testing and the anchor will probably not pass the test requirements.  Epoxy 
adhesive anchors may even strengthen the area at the anchor location (18000 
psi compressive, 5000 psi tensile strength) and cause the cracking to stay
in 
the very low tensile strength concrete-just an idea.

Howard



-----Original Message-----

From: Jan Hermanek [mailto:herzmi(--nospam--at)hotmail.com]

Sent: Tuesday, May 15, 2001 8:44 AM

To: seaint(--nospam--at)seaint.org

Subject: Anchoring in seismic zones





Dear Sirs,


I have a question about anchoring to the concrete.


Our structures are connected to the concrete by chemical or short mechanical


anchors. My question is about anchoring in seismic zones. Chemical anchors 

are not suitable for cracked concrete. In Europe they are not recommended 

because during seismic event concrete cracks. But in the USA I've seen 

evaluation documents for chemical anchors. There you can find that those 

anchors are not suitable for cracked concrete but they are allowed to resist


seismic forces and some document allows even increasing of allowable 

stresses (extra 33% up). I have also understood that mechanical anchors in 

seismic zones are not really welcomed in USA.

Thank you for any suggestion to this topic.


What should I do then to fulfill criteria accepted by US building officials?


Jan Hermanek



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