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Re: ACI 355.2

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I use thru bolts for tilt up retrofit where possible and epoxy bolts
elsewhere.
I use only epoxy hold down bolts.

Stan Scholl, P.E.
Laguna Beach, CA

On Tue, 20 Mar 2001 09:09:08 -0800 "Structuralist" <dennis.wish(--nospam--at)gte.net>
writes:
> Mark,
> Thanks for the summary which goes a long way to at least identify 
> the
> problem. This brings up some questions I have as one who uses 
> anchors in
> residential construction as remedial measures for those omitted by 
> the
> contractor.
> 
> 1. Expansion anchors are commonly used by contractors to secure 
> plates to
> concrete at the edge of slab on grades. I learned some years ago of 
> the
> growing concern with using expansion anchors so close to the edge of 
> the
> slab (roughly 2-inches for a 2x4 plate and 3-inches for a 2x6 plate) 
> and the
> potential for cracking of the slab edge of an anchor under full 
> torque.
> Since learning of this problem, I've replaced expansion anchors with 
> epoxy
> anchors and found that when used to resist shear, most 
> municipalities will
> allow the epoxy anchor to be installed without special deputy 
> inspection.
> However, if used above 1/2 strength working stress capacity for 
> tension
> anchors (tie-downs) then deputy inspection was required.
> 
> Question: What restriction if any will be placed on the use of epoxy 
> anchors
> (or other chemical anchors which do not promote concrete cracking 
> from
> expansion pressure?
> 
> 2. When the provisions for retrofit of Tilt-up concrete to alleviate
> cross-grain tension failures in ledger connections reached its 
> height of
> design in the early 90's the questions of capability of expansion 
> anchors
> was also raised. It was my understanding that expansion anchors were 
> not
> recommended for tension installations in retrofit projects. However,
> Undercut anchors were determined to provide appropriate strength 
> with less
> risk of cracking concrete and reducing strength. Again, I have opted 
> to use
> chemical anchors over expansion or undercut anchors as common sense 
> dictated
> that the bond from chemical anchors would be superior to compression 
> type
> anchors and would do less damage.
> 
> Question: Is this the perception of other engineers and if so, what 
> major
> consequence will there be in retrofit work for the restrictions 
> placed on
> compression type anchors that can not be resolved with possible 
> changes in
> installation requirements of chemical anchors that would insure 
> appropriate
> strength, mixture and installation without the need of deputy 
> inspection?
> 
> Question: This leaves the wide range of historic uses for 
> compression and
> undercut anchors on interior slabs and with appropriate edge 
> distance on
> foundations. What evidence is there of reduced tensile strength that 
> has not
> been tested by other manufacturers such as ITW and Covert and is 
> this a
> major concern?
> 
> Dennis S. Wish, PE
> 
> > -----Original Message-----
> > From: Mark Gilligan [mailto:MarkKGilligan(--nospam--at)compuserve.com]
> > Sent: Tuesday, March 20, 2001 6:47 AM
> > To: INTERNET:seaint(--nospam--at)seaint.org
> > Subject: Re: ACI 355.2
> >
> >
> > I have received input from John Silva of Hilti and Richard 
> Klingner who is
> > on the committee that wrote ACI 355.2 and I have some comments on 
> several
> > related topics.
> >
> > Topic 1
> >
> > The manufacturers opposing ACI 355.2 claim that the test  method 
> is
> > un-necessary, that its adoption will require engineers to assume 
> concrete
> > is cracked, and will require changes is practice.
> >
> > This seems to ignore the fact that the ICBO  Evaluation Reports
> > for anchors
> > (Including ER-1372 issued to ITW RAMSET/RED HEAD) state that the
> > values are
> > limited to installation in uncracked concrete.  To me, this means 
> that if
> > the engineer determines that the concrete is cracked the ICBO 
> approval is
> > not valid.
> >
> > The status quo that the manufacturers opposing ACI 355.2 are 
> proposing is
> > one in which the engineer is left with no guidance.  One strategy 
> would be
> > to not use post-installed concrete anchors where concrete is 
> assumed to be
> > cracked, but somehow this does not seem to be what is implied by 
> the
> > www.alertaci355-2.com web site.  That web site seems to imply that 
> we
> > should use these anchors in cracked concrete and not worry despite 
> what
> > ICBO says..
> >
> > Unless you can change the ICBO acceptance criteria there is a need 
> for
> > anchor values in cracked concrete and for anchors subject to 
> earthquake
> > loading.  It appears that ACI 355.2 provides us with a way 
> forward.  The
> > manufacturers opposing ACI 355.2 have not offered any alternative.
> >
> > It appears that one of ITW's sister-operations in France, SPIT has 
> an
> > anchor that can pass the ACI 355.2 criteria so we should be 
> assured that
> > there will be more than one manufacturer that will be able to 
> provide
> > anchors that comply with ACI 355.2.
> >
> > The ICBO acceptance criteria will be discussed at the ICBO ES 
> public
> > hearing on Tuesday, April 8 at the Furama Hotel near LAX.
> >
> >
> > Topic 2
> >
> > On the question of whether any anchor failures have been reported 
> Richard
> > Klingner, who monitors this list, states that there have been 
> instances of
> > anchor failure.   Apparently because the investigators were not 
> looking
> > specifically for failures due to cracks in concrete the presence 
> of cracks
> > were not reported.  A post-installed anchor that fails as a result 
> of
> > cracked concrete will manifest itself as an anchor that simply
> > comes out of
> > a hole.  Do we have a situation where because we have blinders on
> > we do not
> > see a problem?
> >
> > This is a partial answer but it would still be desirable to have
> > a specific
> > example of and anchor failure due to cracked concrete.
> >
> > It is commonly accepted that concrete cracks, and there appears to 
> be no
> > dispute that many anchors in cracked concrete have lesser 
> capacities, at
> > least when tested as per ACI 355.2.  The question then becomes one 
> of why
> > have we not seen more failures?
> >
> > Some of the possible reasons that  we have not seen more failures 
> are:
> > --Cracking is often associated with factored loads which do not 
> commonly
> > occur.
> > --The loads on anchors may be less than assumed.
> > --The use of multiple anchors in a connection may provide enough 
> capacity
> > to prevent failure even if one anchor fails due to cracking.
> > --The test procedure may not reflect the installed situation.
> >
> > I would be interested in specific reasons why the test procedure 
> is
> > believed to be not reflective of field conditions.
> >
> > Given that our codes are based on the acceptance of a certain 
> number of
> > failures it could be argued that one could ignore the impact of 
> cracks on
> > most connection designs.  The problem then becomes one of making 
> sure that
> > the tradeoff of failures against construction cost is reasonable.  
> This
> > typicall consists of identifying the total annual loss due to 
> failures and
> > comparing it with the   cost of preventing the loss.   I would 
> welcome a
> > letter from one or more of the manufacturers showing a cost 
> benifet
> > analysis of such a trade-off.
> >
> > In the case of connections that have to carry load during and 
> after an
> > earthquake I do not think that it is reasonable to ignore concrete 
> cracks
> > in determining connection capacities.  During earthquakes we will
> > often see
> > loads on the concrete in excess of those used in design.  In 
> addition the
> > loads on the anchors during an earthquake may be considerably 
> larger than
> > assumed.  These realities combined with the relatively infrequent
> > occurrence of earthquakes, and thus limited experience with 
> anchors in
> > these situations, argues that we should not ignore the impact of 
> cracks on
> > anchor capacity when dealing with earthquake loading.
> >
> >
> > Topic 3
> >
> > The manufacturers objecting to the adoption of ACI 355.2 state 
> that:
> >
> > "The European Commission has determined that the new code does
> > not meet the
> > basic criteria of the Construction Products Directive, thus 
> creating
> > unnecessary burdens for builders, producers and consumers alike! 
> The
> > Commission's Directorate General for Enterprise directed the 
> European
> > Office of Technical Approvals (EOTA) to determine a mechanism to 
> address
> > these complaints and to report its proposed method to accomplish 
> this
> > mandate, including substantive revisions to the ETAG. "
> >
> > Apparently this issue was raised by ITW.
> >
> > According to John Silva of Hilti, who on occasion has monitored 
> this list
> > server, it is not clear that this review will result in any 
> significant
> > change.
> >
> > There appears to be a difference of opinion as to the  
> significance of any
> > changes to the ETAG documents.  Can somebody list the specific 
> changes and
> > comment on the significance of each.
> >
> >
> >
> > A number of people have expressed concern about hearing of this 
> problem at
> > the "last moment".  It should be noted that there was aa Aug 
> 28,2000
> > posting to this list by Kent Carlson in  which he summarized the 
> issues.
> >
> > Mark Gilligan
> >
> 
>