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Re: [SEAOC] Tiltup Retrofit Anchors

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usdwpydp(--nospam--at) wrote:
> ** Reply to note from IBMMAIL(I1720810) 02/21/96 11:03pm
> >  From: CarlS95(--nospam--at)
> >  Subject: ìSEAOC? Concrete Anchors in Tilt-Ups
> >  I'm looking for opinions, friendly or otherwise:  Are expansion-type
> >  anchors, such as Hilti Kwik-Bolt II, appropriate for out-of-plane anchors in
> >  the wall-to-roof connection to retrofit existing, pre-1971, concrete tilt-up
> >  buildings?  The configuration would consist of concrete anchors drilled
> >  through the wood ledger, and connected to the wood joists with Simpson
> >  holdowns or similar hardware.
> Carl,
> We are applying an approach which I feel comfortable with- on new
> retrofit anchors, we are using strictly epoxy-grout anchors. Our
> experience with any type of expansion anchor that relies on friction to
> retain it in the concrete is that they fail under dynamic (seismic)
> loads well below their static capacity. Furthermore, we have noticed
> that most manufacturers allow a large amount of anchor displacement to
> occur in testing, and as long as it is 'holding', use the ultimate
> pullout value, regardless of anchor displacement. This is not acceptable
> under dynamic conditions of load reversal.
> On existing buildings fitted with expansion anchors in the roof to wall
> connection, if the calculated load based on the Division 91 criteria is
> well below the LARR allowable value (use judgement, but 50% of allowable
> should be a clear case), we are approaching on a case-by-case basis,
> approval of the existing anchors by calculation.
> .bc THONLE
> Thomas D. Honles, S.E.
> DWP Energy Services Structural Engineering  (213)367-0006
> Vines:thonle@pdc_csess_struc@ladwp          (213)367-0066 Fax
> Internet E-Mail: usdwpydp(--nospam--at)
> ...

I concur with Tom Honles assessment of expansion anchors, although the 
Tilt-up committee had taken a position on "under-cut" anchors and felt 
that these would be perferable to expansion anchors. The Under-cut 
anchor, though, requires a special bit since the end of the hole is 
widened (bell shaped) to gain a greater hold with less tension against 
the sides. 
I perfer, and always have - especially with retrofit into poorer grades 
of concrete - to use the Hilti Hit anchor system with their C-100 epoxy 
adhesive for solid based materials. Covert Anchor uses a similar 
adhesive as does a typical SAE 1018 threaded rod and the Simpson 
"Epoxy-Tie" adhesive system.
Hope this helps.
Dennis S. Wish PE