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RE: Welding against concrete

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Bill, 

It is a common detail.  I have not seen any failures in the field due to the
local high heat on an embedded steel weld plate.  However, I do see it as a
concern and a potential problem.  Although heat is conducted fairly well in
steel, it is not conducted well in the concrete.  There is generally a
fairly small area of heat effected concrete due to "normal" welding.

To avoid having a problem I:
*	Locate my embedded studs away from the area where the field weld is
to occur
*	If an embed stud must be located opposite a field weld, allow for it
by assuming you've lost about 1/2" of concrete at the stud plate interface.
(This may effect the shear capacity to a degree)
*	Minimize the weld size avoiding multi pass welds (make 1/4" welds
work if possible)
*	If larger welds are necessary, I require a multi-pass prequalified
weld (specify 1/4" maximum weld per pass)  with instructions on waiting for
the heat to dissipate prior to the next pass (use the crayons if you are in
doubt)
*	Design welds that do not require preheat
*	Use a minimum embed plate thickness of 1/2"

I have had occasion to study structural steel trusses that were highly
stressed and welded while members were subjected to large tensile loads.  We
actually stressed members in the lab and welded plates on them to see if the
heat effected area would be large enough to cause a tensile failure.
Obviously the weld was white hot molten metal, but the back side of a 1/4"
angle was just red hot.  It was not a problem for the trusses.

I have also witnessed welds in a steel fabricating shop performed with steel
plate placed directly on a concrete slab on grade, and there was no damage
to the concrete.  Granted the concrete contact was not the same as an
embedded plate, and that is why I try to minimize the potential for
problems.

Regards,
Harold Sprague

> -----Original Message-----
> From:	Polhemus, Bill [SMTP:wlpolhemus(--nospam--at)sbinfra.com]
> Sent:	Wednesday, February 09, 2000 9:49 AM
> To:	'seaint(--nospam--at)seaint.org'; 'structx(--nospam--at)topica.com'
> Subject:	Welding against concrete
> 
> I have a situation where I need to weld (vertical position) some 1/4"
> plate
> that is set against a concrete wall. The weld would just be a partial-pen
> weld, AWS prequalified weld joint designation B-P1c.
> 
> My question is: is there anything I must do to protect the concrete
> directly
> behind the weld? Or is this not a problem?
> 
> Your comments, please.
>