Welding on joist retrofits

[kc9508]

Hi - new to this forum, but based on my experience with this site I'm hoping someone may be able to shed some light on this question for me.

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.

 

[MotorCity]

Never heard that one before, as the method of reinforcement you describe above is quite common. Here is my two cents. Say the insulation does melt...so what. You are left with an extremely small un-insulated area of roof (as long as it does not catch on fire of course). But more realistically, I think the roof deck and the 1.5" air gap between the joist and insulation will greatly dissipate the heat generated by welding.