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RE: ACI 355.2

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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
>