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RE: More On Ungrouted Baseplates for Traffic Signal/Signage Struc ture s

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Harold,

In case you ever get involved with the subject of head bearing pressures
again, Werner Fuchs did extensive research in this area at the University of
Stuttgart in the late 1980s.  In most cases, limiting the head pressure to
12-13f'c will prevent progressive crushing.  The other guy who is an expert
on headed anchors (as in headed rebar) is John Wallace at UCLA.

On the subject of double-nutted anchors without baseplate grout for tall
mast-type structures, I have always been amazed at the number of anchorages
I see constructed this way.  A couple of things to keep in mind.  You are
correct, Bill, in assuming that compression loads (including overturning)
are taken into the anchor and are resisted at the head.  If the anchor has
been embedded with tension loads in mind, the distance from the head to the
bottom of the foundation may not be adequate to carry this load.  Lateral
loads are carried in bending in the anchors.  A quick calculation of their
bending capacity will show that the lateral capacity of a connection done
this way is minimal compared to the nominal shear capacity of the anchors.

Hilti has done some limited research on the subject of optimizing the
performance of the grouted baseplate detail.  Essentially, (and perhaps not
surprisingly) we found that roughening the surface of the concrete before
placing the grout enhances the lateral resistance substantially.  Providing
nominal reinforcing in the grout layer also helps.

>From my own earthquake reconnaissance experience, I've seen enough failed
anchor bolt details to convince me that they are generally being
under-designed.

Bill, I can recommend the following additional references on the design of
anchorages (if they weren't already mentioned):

Fuchs, Eligehausen, Breen, "Code Background Paper:  Concrete Capacity Design
(CCD) Approach for Fastening to Concrete" ACI Structural Journal Vol. 92 No.
1  Jan.-Feb. 1995

Balogh, Eligehausen, "Code Background Paper: Behavior of Fasteners Loaded in
Tension in Cracked Reinforced Concrete", ACI Structural Journal Vol. 92, No.
3 May-June 1995

CEB Design Guide, Design of Fastenings in Concrete, Thomas Telford
Publishing, London 1997

I've been told that the last one (CEB) is somewhat expensive, but it gives a
good overview of the subject.  Finally, I would note that if you cannot get
sufficient tension capacity from your anchorage using a concrete cone
failure model, you probably need to think in terms of transferring the load
directly to reinforcing in the foundation using hairpins or other means.
Remember also that without sufficient transverse reinforcing, splitting may
control your capacity.

Regards,

J. Silva, SE

silva(--nospam--at)hilti.com

-----Original Message-----
From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
Sent: Wednesday, May 17, 2000 9:14 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: More On Ungrouted Baseplates for Traffic Signal/Signage
Struc ture s


Bill,

Thank you for your kind words.  I too have learned a lot from this list.  I
am glad that you find my contributions helpful.

It has been several years since I obtained these documents, but I believe
that I got them from Dr. Klingner.  I was doing some research on
substantiating the enormous bearing pressures (well beyond ACI 318 limits)
at the head anchorage of anchor rods.  All the research showed that the
bearing stress (confined local crushing)  was not a problem.  

Regards,
Harold Sprague


> -----Original Message-----
> From:	Polhemus, Bill [SMTP:wlpolhemus(--nospam--at)sbinfra.com]
> Sent:	Wednesday, May 17, 2000 9:32 AM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	RE: More On Ungrouted Baseplates for Traffic Signal/Signage
> Struc ture s
> 
> Thanks, Harold. I had checked with them yesterday, and did not even found
> where I could ORDER these pubs.
> 
> Did you get these references from the work that you mentioned?
> 
> I'm going to contact them about ordering.
> 
> Regards.
> 
> [N.B.: May I say that I appreciate--actually, I'm breathless at--your
> depth
> of knowledge of so many subjects. You humble me greatly, as I don't
> believe
> I have even a fraction of these facts that you seem to be able to come up
> with off the top of your head. What a rare talent. I'm envious, but I'm
> also
> glad that I and others have you available!]
> 
> -----Original Message-----
> From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)bv.com]
> Sent: Tuesday, May 16, 2000 5:24 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: More On Ungrouted Baseplates for Traffic Signal/Signage
> Struc ture s
> 
> 
> Bill,
> 
> The Center for Transportation Research web site is:
> http://www.utexas.edu/depts/ctr/, but I don't think that the reports are
> on
> line.
>