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RE: ASTM A970 welded headed anchor problems

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Harold,

Thank you for your reply.  To clarify: ASTM A970-98 covers ductile 
welded or forged headed concrete reinforcing bars and the 
contractor has elected to use the welded flavor.  

The head is a piece of ASTM A36 7/16" plate, 1.5" square, and the 
bar is ASTM A706 #4.   The pre-production tensile test limits yield 
to 60 ksi min, 78 ksi max; tensile to 80 ksi min and at least 1.25 
times actual yield; elongation to 14% min in 8"; and failure must be 
at least one bar diameter from head, in the parent material. There 
is a 90 degree bend test, too.

Regarding ASTM A496 deformed bars-I do not have the current 
edition but my 1993 says there is no elongation requirement.  I 
wonder if an A496 deformed bar would meet A706 yield, tensile, 
and elongation requirements.

After my first email, but before I got your reply, the contractor
ran another series of tests with a modified joint and 200 deg F 
preheat.  They obtained better results, but again had difficulty with 
the elongation: one sample achieved 9.4% elongation and failed in 
the HAZ (but more than one diameter from the head), with 14% 
reduction of area; the other acheived 14.4% and failed in the parent 
material, with 39% RA.  

Dave


> Dave,
> 
> I am having a hard time understanding the problem.  A970 is for headed
> studs.  A 706 is for weldable rebar.  What is being welded and what is it
> being welded to?  What testing is required?
> 
> You describe the failure at the head presumably of a stud, but then you
> write about a failure in the HAZ of the rebar.  I am sorry, but I am
> confused.
> 
> The carbon equivalence requirements of A970 is the same as A706 with 0.30%
> max C and a CE max of 0.55%.  This should be "weldable".  Reduced ductility
> is generally due to high carbon.  You can make a weld more ductile by the
> application of preheat.  If you are welding a stud, you should be using
> fusion welds as opposed to a flux core arc weld FCAW.  In either case it
> should still give you a ductile weld.
> 
> If the welding is FCAW and there is any significant breeze, you could be
> loosing the shielding.  This has been a recurring problem for projects I
> have worked on.  Try using a stick electrode, add a wind screen, or augment
> the shield with an additional gas shield like C02.  Also check the date on
> the wire.  Some old flux core wires can take on water.
> 
> If the welding is OK I would be suspicious of the CE of the bar because you
> describe the failure along the HAZ of the rebar.  Have the bar tested for
> CE.  
> 
> The easiest thing to do is use a deformed bar anchor as opposed to welding
> rebar.  If it is rebar that you want to weld to carbon steel use the DBA.
> The DBA has a point on the end and uses a fusion weld the same as if it was
> a headed stud.  The weld takes seconds per DBA as opposed to 15 or 20
> minutes for preparing and welding pieces of rebar.  The fusion welds for
> DBA's are usually very ductile, and easy to obtain.
> 
> Regards,
> Harold O. Sprague
> 
> > -----Original Message-----
> > From:	Dave Evans [SMTP:DEvans(--nospam--at)tnh-inc.com]
> > Sent:	Monday, October 15, 2001 8:53 PM
> > To:	seaint(--nospam--at)seaint.org
> > Subject:	ASTM A970 welded headed anchor problems
> > 
> > A contractor is having difficulty achieving the required elongation 
> > (test = 3 to 5% vs. required 14%) and failure location (test = 0.32" 
> > to 0.38" from head vs. required 0.46").  Yield and tensile are ok and 
> > failure is cup and cone in HAZ in rebar.
> > 
> > Weld is chisel-point full-pen with FCAW 80T1.
> > Rebar is #4 A706.
> > 
> > Contractor is going to try building weld farther away from head to 
> > get failure location away from head, and is going to try preheat to 
> > help elongation.  
> > 
> > Any comments or ideas on how to improve performance would be 
> > appreciated. 
> > 
> > Thanks,
> > Dave Evans, P.E.
> > TNH, Inc.
> > 
> 
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