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RE: Embedded Anchor Bolts In Compression

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Mark,

The reason that bond for plain bars went out of fashion was due to the
variability, and the potential for catastrophic failures.  The original bond
strengths were predicated on very limited testing of hot rolled mild steel
which had a lot of porosity at the surface.  Cold rolled shapes did not have
this surface porosity.  More modern rolling mills had much less surface
irregularities than older mills even for mild steel.  Bond strength testing
to plain steel could not be validated.

Personally I saw an iron worker back out an unheaded anchor bolt that was
embedded 4 feet into a drilled shaft.  It backed out just due to the tension
from tightening with a plain spud wrench.  According to ACI 318-63, the
embedment was enough to fully develop the bolt.  ACI 318-63 was the last 318
that allowed for bond to plain steel.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Mark Baker [SMTP:shake4bake(--nospam--at)earthlink.net]
> Sent:	Monday, October 23, 2000 9:41 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re: Embedded Anchor Bolts In Compression
> 
> Just because it is not in fashion anymore to design anchor bolt embedment
> based upon bond.......
> 
> Look back at mid 60's vintage ACI manual for bond strengths at various f'c
> and bolt diameters. Let me know if you can't find it.
> 
> Mark
> 
> ----- Original Message -----
> From: Bill Polhemus <bpolhem(--nospam--at)swbell.net>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Monday, October 23, 2000 3:26 PM
> Subject: Embedded Anchor Bolts In Compression
> 
> 
> > I know we talked a little about this a few months back, but now that I
> have a
> > little more knowledge (a "little knowledge" being, of course, a
> dangerous
> thing)
> > about the topic, I'd like to recast the question I asked before.
> >
> > In some instances there are advantages to NOT grouting structural column
> base
> > plates. For example, our stated DOT does not allow grouting of column
> base
> > plates for overhead traffic sign structures, which are typically hollow
> sections
> > and have cables or conduit running up into them from the bottom (the
> base
> plates
> > have concentric openings to allow this). They are afraid that condensed
> moisture
> > will build up inside the columns and cause accelerated corrosion.
> >
> > Thus, no grout under the base plates, and the compression AND tension
> forces are
> > carried by the anchor bolts, the plate resting on the levelling nuts.
> >
> > An embedded anchor bolt in compression would tranfer the column forces
> into the
> > concrete pedestal by bearing on the nut at the bottom of the bolt. But
> these
> > forces are bound to be large, and using the ACI code-calculated bearing
> strength
> > of the concrete under the nut (ACI 318-10.17.1) is not going to be
> sufficient
> > for such a force.
> >
> > Does anyone have any experience with this? What did you use to determine
> > adequacy?
> >
> > I seem to recall that research into anchor bolt failure mechanism showed
> that,
> > because of localized confinement, the bearing at the nut allowed was
> typically
> > on the order of many times the ACI 318 code calculation, when the bolt
> is
> in
> > tension. Not sure if the same would apply here.
> >
> > Look forward to your input.
> >
> >
> 
>