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Re: COMPRESSION Force On Anchor Bolts/Rods

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To Q. one

You may get an idea from ACI 318-99 Section 12.16.4 "End-Bearing Splice".
In case of compression, splice is made between anchor bolt and concrete.
Unless you use deformed wire anchor, that is, if you use headed anchor,
shank of the bolt dose not provide any resistance to compression or tension.
Like the upward tension, all the compression is concentrated on anchor
head. 
So, if the foundation is shallow, you may have to check downward punching
(say blowout)and concrete bearing at the bottom of anchor head.  

To Q. two

Early draft revision of ACI 349-01 App. B once simply described about
the effect of  reinforcement on the anchor bolt. After that withdrawn.
Currently, you cannot rely on reinforcement. 
But. ACI 349-97 and earlier, there are several details of  rebar reinforcing.

In any cases, you cannot use rebar provided for concrete structure against
flexure, shear and axial. Stress induced from anchor bolt is not well quantified.

Best Wishes





----- Original Message ----- 
From: Bill Polhemus <bill(--nospam--at)polhemus.cc>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, December 12, 2001 7:42 AM
Subject: Q: COMPRESSION Force On Anchor Bolts/Rods


> QUESTION ONE.
> 
> I am obliged to design the anchor rods for a base plate which is NOT grouted
> so that ALL forces are transmitted to the anchor rods via hold-down AND
> leveling nuts. I gather this isn't an altogether uncommon thing since the
> baseplate design program I'm using actually allows it as a condition for
> design.
> 
> My problem is in considering the embedment of the bolts and the capacity
> thereof to resist compressive forces. If I have a steel-plate anchor
> mechanism, it seems to me that the anchorage and the encapsulating concrete
> are going to see the same kind of effect with the bolts in compression as
> from tension, only in reverse (i.e. there will be an effective conical
> "pushout" area BELOW the anchorage).
> 
> As you might expect, because of the gravity loading the compressive force is
> actually GREATER than the tension force in a given bolt.
> 
> It seems to me as a first approximation, then, that you'd need at least as
> MUCH concrete below the anchorage as would be required above it, to keep the
> anchor rod from "plunging" or the anchorage zone from blowing out.
> 
> Has anyone looked at this in detail? If so, what design assumptions did you
> make and why?
> 
> QUESTION TWO.
> 
> Using the publication "Strength Design of Anchorage To Concrete" by Ronald
> A. Cook, published 1999 by the Portland Cement Association, and which
> purports to be a "late draft" of the proposed provisions for design of such
> anchorages to be included in the next edition of ACI 318, I have NOT been
> able to determine if the designer may utilize surrounding reinforcing bars
> that cross "concrete cone failure" boundary to increase the concrete
> breakout strength.
> 
> I have seen this utilized in other instances, and it is inferred in ACI 318
> ? 11.7.7 (esp. see the accompanying Commentary), so it seems logical you
> could do that in this instance, but I don't see where Cook explicitly
> mentions it.
> 
> Any comments are very welcome.
> 
> Thanks.
> 
> 
> 
> William L. Polhemus, Jr. P.E.
> Polhemus Engineering Company
> Katy, TX, USA
> Phone (281) 492-2251
> FAX (281) 492-8203
> email bill(--nospam--at)polhemus.cc
> 
> 
> 
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