welded side laps on metal deck
welded side laps on metal deck
(OP)
Anyone have any experience with welding the side laps on 1.5B roof deck? I have always specified screws, but specified welds this time around for aesthetics (the Arch didn't want to see any screws b/c the underside of the deck is exposed). This is now backfiring on me, because apparently it is nearly impossible to weld the 2 sheets together without burning through. I upsized the deck from 22 to 20 ga to try to mitigate this problem, but the welders still can't avoid the burn through. I have come across a few "references" that say burn through is to be expected or that it is the rule and not the exception, but I don't see how this burn through cannot undermine the strength of the weld, not to mention it looks pretty bad. If this is such an issue, why do all the metal deck manufacturers publish diaphragm strength data for welded sidelaps?






RE: welded side laps on metal deck
RE: welded side laps on metal deck
The side laps could have been punched. This is done with a special tool that clips the sheets together. Haven't seen one used in years, but they were available at one time.
Assuming you are in the us, hopefully you required that the welders be certified to the sheet metal code (AWS D1.3) rather than just D1.1
RE: welded side laps on metal deck
Dik
RE: welded side laps on metal deck
John Southard, M.S., P.E.
http://www.pdhlibrary.com/
RE: welded side laps on metal deck
John Southard, M.S., P.E.
http://www.pdhlibrary.com/
RE: welded side laps on metal deck
I am considering using screws installed from the bottom side of the deck. That is an idea that the GC has already proposed. Any other thoughts?
Back to the welding issue... upon reviewing AWS D1.3, arc spot welds (a.k.a. puddle welds) seem only to be allowed for sheet steel to supporting structural steel, not sheet to sheet, so why does the SDI allow puddle welds on side laps? Also, the AWS D1.3 qualification test for arc seam welds (a possible alternative to puddle welds) shows a standing seam that has been crimped together so there are 3 plies in contact, not just 2. Figure 2.12 impies that this crimping helps with the burn through issue. It doesn't appear to address just 2 plies lapped in the horizontal plane.
Have any of you actually successfully used welded side laps before? Personaaly, I am leaning toward avoiding them in the future.
RE: welded side laps on metal deck
From the Steel Deck Institute Manual of Construction:
"Burn holes are the rule rather than the exception and an inspector should not be surprised to see them in the deck. The weld develops its strength by holding around the perimeter. A good weld will have 75% or more of its perimeter working."
The manual is online at http://www.sdi.org/whites/moc2.pdf
RE: welded side laps on metal deck
Dik
RE: welded side laps on metal deck
RE: welded side laps on metal deck
All, I have decided to increase the number of welds to the supporting structure and allow screws driven from the bottom on the sidelaps to achieve the same shear strength as the original attachment pattern with welded sidelaps. Thanks for the input.
RE: welded side laps on metal deck
I have successfully specified welded side laps before... at least as far as I know. However, we had the erector do some tests prior to construction to see if it could be done. I believe we used 18 ga deck though, not 20ga.
RE: welded side laps on metal deck