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RE: ASTM A970 welded headed anchor problems

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Dave,

A 496 requires 75 ksi yield and 85 ksi ult yield.  Nothing definitive on
elongation, but there are bend requirements. 

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	Dave Evans [SMTP:DEvans(--nospam--at)tnh-inc.com]
> Sent:	Tuesday, October 16, 2001 1:35 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: ASTM A970 welded headed anchor problems
> 
> 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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