Joist retrofit welding

[kc9508]

I'm working on a project where we have designed some retrofits for existing roof joists to increase their capacity. In particular, we are proposing to weld a 5/8" rod to each top chord of the joists (which are a pair of 1.75"x2"x1/4" angles). The roof system consists of metal deck (supported by the joists) with insulation and membrane on top. The rod needs to be welded to the angles with 2" long stitch welds every 12" o.c. The contractor has expressed concern that when he welds to the top leg of the angle (i.e. in direct contact with the rib of the metal deck) that he may melt/burn the insulation. From what I've read, the proposed retrofit detail seems like a pretty common one, so I'm wondering if the concern is valid or if there are means/methods that should be used to reduce or eliminate this concern? Metal deck is 1.5" deep.

Thanks in advance.

 

[KootK]

It's a very common detail and I've never heard of said problem developing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

Should not be an issue. The weld will only heat the bottoms of the flutes and the insulation sits on the top of the flutes. Since only a two-inch weld, it could be done in the void between flutes, so absolutely no influence!

 

[kc9508]

Thanks Ron and KootK, that makes me feel much better!