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RE: ASTM A970 welded headed anchor problems

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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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