Steel Deck Bearing on Slope

[lexeng18]

Hi all. I am seeking advice on some detailing issues with an interesting framing layout I am working on. See attachment and forgive my penmanship.

It is a conventional steel framed octagon with a 3:12 roof slope. Steel deck spans parallel to roof slope. Two questions:

1) For the low eave condition, Sect. A, this is a fairly common deatail and I am comfortable with it. However, 3/16” plate seems like maybe overkill for this situation. Could I argue 12 or 14ga flat stock? It’s not obvious to me what calculation I could do to verify what is acceptable in this situation.

2) For the high eave condition, due to architectural reasons the decking needs to stop at the face of the tube. Therefore I need deck bearing along this face. The same question as #1 above, but also would a better detail be to provide a bent plate vs just some flat stock with a bevel weld?

Intuitively I am thinking a bent plate would facilitate fabrication more (not having to hold flat stock at an angle while making a bevel weld) but I am not familiar with fabrication techniques enough to know.

 

[phamENG]

I would suggest sticking to steel plate. Welding light gauge to structural steel can be done, but it's tricky and easy to screw up (burn through the lighter material before the base material is sufficiently heated).

As for the bent plate vs flat stock, it'll depend on your welds. 3:12 should fall within the acceptable range for a prequalified fillet weld (see the SCM chapter on welds or AWS D1.1), so if you can get enough strength out of a single weld you're looking at less material, less fabrication (don't have to cold bend the plate), and less welding (bent plate will have a 3/16" fillet on the bottom and a flare bevel at the top). Setting up a jig to hold the plate at the correct angle shouldn't be an issue.

 

[XR250]

I don't see an issue with bent 14ga sheet for this. It is regularly welded to red iron. The deck installers will appreciate the lighter thickness if they are screwing it down.