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RE: Rebar breaking

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Mike,

You are kind of correct.  A706 rebar will meet most of the A615
requirements.  Obviously, the reverse is not true.  Rebar meeting A615 will
probably not meet A706.  

The MINIMUM yield strength of 60 grade A706 and 60 grade A615 will be 60
ksi, but the minimum tensile strength of A706 bar is 80 ksi, and the minimum
tensile strength of grade 60 A615 bar is 90 ksi.  

There are other departures that require care for dual certification.
Obviously if the bar is dual certified the minimum tensile strength will be
90 ksi to meet A615.  There is also a requirement in A706 for a minimum
ratio of tensile to yield strength of 1.25.  So if the minimum tensile
strength is 90 ksi (for 615 compliance) the maximum yield (for A706
compliance) would have to be 72 ksi.  This is an issue that is not that well
addressed in special moment resisting concrete frames when calculating the
Mp.  

If the special inspector is looking at a bunch (bunch = 2 times one gob) of
steel, and some of the rebar is specified to be A615 and some A706, the
marking would tell the inspector (with the S symbol) that it meets A615 bar
requirements.  It was a similar issue when A36 and A572 started to be dual
certified.  For many years Nucor only ran one type of steel, but it would
meet both A36 and A572.  

BTW older rebar will not be marked the same.  I am not sure when A615
started to require the S.  Older bar (circa 1975) only used the S to
indicate supplemental requirements.  The ACI A615-75 used "N" to indicate
compliance to A615.  It also stood for new billet.  

I am looking forward to the demise of A615 bar.  I have had more than a few
problems with A615 bar, but it is the vast majority of rebar in the field
today.  It is a terribly loose specification, and the steel is very brittle
as the original post pointed out.

Regards,
Harold O. Sprague

-----Original Message-----
From: Mike Murphy [mailto:Mike_Murphy(--nospam--at)Ameron.com] 
Sent: Wednesday, October 08, 2003 12:16 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Rebar breaking

I was under the impression that rebar that meets A706 always meets the
requirements of A615. The ASTM A706 specification is just a stricter subset,
so to speak, of the A615 requirements.

Is this not correct? 

Harold's comments that bars marked S and W meet both specifications has got
me wondering. A bar marked W (for A706) would meet both specifications if my
understanding is correct

Regards,
Mike  Murphy

-----Original Message-----
From: Sprague, Harold O. [mailto:spragueho(--nospam--at)bv.com] 
Sent: Tuesday, October 07, 2003 9:30 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Rebar breaking

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
 



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