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RE: Rebar breaking

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I would worry too.  

In this country, the normally specified rebar is for ASTM A615.  A 615 has
no upper limit for carbon.  It is common for A615 bar to have 0.45%or 0.50%
carbon, but there is no set upper limit of carbon in the steel.  It is a
medium to high carbon steel.  High carbon steels can have a propensity for
carbon "lenses" to develop in the rolling process.  These local areas have
even higher carbon concentrations resulting in very poor resistance to
impact, and do not bend well.  

Look closely at the bends, and you may see small cracks in the bend areas.
The rebar may not be in compliance with Section 10.1 of A615.  Do some dye
pen tests to try to find cracks in the bend area of the rebar.  Get the
testing done as well.  Require the mechanical testing.  I would get
chemistry done, even though there are no limits in chemistry for A615.  Have
them do the bend test too.  

I hope that you specified that you wanted the mill test reports (heats).  If
they are not required to be submitted in your specification, they are often
thrown out when the rebar ships from the fabrication shop to the field.  

Check the bar marks, it is probably marked with an "S" after the size
designation which indicates that it is A615.  

Compare A615 bar to A706.  It is a world of difference.  A706 is marked with
a "W" after the size callout.  Carbon is limited to 0.30% maximum.  They
also limit the carbon equivalence to 0.55%.  The chemistry of A706 makes it
much more ductile, resistant to impact, and weldable than A615.

Even though A615 is allowed in certain high seismic applications, I am not a
big fan, and when there is any doubt, I tend to specify A706 bar.

By the way, when an S and W are stamped on the bar after the size, it is a
dual certified rebar to A615 and A706.

Regards,
Harold O. Sprague

-----Original Message-----
From: Michael L. Hemstad [mailto:hemstad.ml(--nospam--at)tkda.com] 
Sent: Tuesday, October 07, 2003 10:57 AM
To: seaint(--nospam--at)seaint.org
Subject: Rebar breaking

I have a project under construction using drilled pier foundations.
Each pier has 6-#7 bars with 90 degree hooks, projecting from the top.

A backhoe working around the piers snags the hooks, and they break.
They apparently don't bend and deform; they just snap off in the middle
of the bend. They have broken perhaps 15 hooks so far.  I've never seen
this happen, and suddenly it's happening a lot.  Call me a worrier, but
I don't like it.

I am in the process of obtaining mill certs, and am considering material
tests.

Is this problem seen often, and is there an identifiable cause?  Does
anyone have any recommendations as to testing of the rebar?

Thanks for any help or advice.

Mike Hemstad, P.E.
TKDA
St. Paul, Minnesota
 

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