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Re: Welding Through Metal Roof Deck

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If I understand your setup here you basically have two structural members crossing perpendicular to each other with a metal deck sheet metal in-between and you want to fillet weld the two structural members together with fillet welds across their intersection.  In regards to the welding you have a couple of problems.  The first issue is that the sheet metal is causing a gap between the two structural members (i.e. the root opening is greater than zero) which is not a big issue as long as it does not exceed 3/16 inch.  You would still need to add the root opening dimension to your required fillet weld leg dimension.  The second issue would be that the sheet metal would melt and possibly get into the liquid weld metal pool which would be an impurity causing unknown metallurgical issues with the weld properties.  As a minimum I suspect you would need an approved Welding Procedure Specification (WPS) qualified by testing with a Procedure Qualification Record (PQR) since this situation does not seem to be covered by either AWS D1.1, Structural Steel, or AWS D1.3, Sheet Steel.

Thomas Hunt, S.E.

"Adair, Joel" <jadair(--nospam--at)>
03/02/2009 11:04 AM
Please respond to seaint
Welding Through Metal Roof Deck

To all the Welding Experts on the List:

I have a project that has a lot of exposed steel structure.  We're using
a decorative steel roof deck that is going to be exposed in many
locations on the interior, but also on the exterior after it crosses the
perimeter beam and becomes the soffit of the roof overhang.  The
architect wants to have deck overhangs longer than what the deck can
cantilever, but doesn't want to see outriggers, so I've proposed putting
2"-deep outriggers above the deck, where they'll be buried between the
deck and rigid insulation.  However, this means that the outriggers
would have to be welded to the perimeter beam and the first interior
joist by intentionally burning through the 20-gauge deck as the fillet
weld between the outrigger and the roof beam/joist is made.

Should I be concerned about making this weld?  Should I come up with an
alternate connection detail?

Thanks for your insights.

-- Joel

Joel Adair PE
Structural Engineer


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