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Stairwell Enclosure Ideas - Cold Formed Roof Trusses? 4

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Structural
Jan 15, 2021
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I'm pricing a job as a metal subtrade for a GC, and they already have a design for the roof structure. My problem is the so-called design is A) lacking so many details that as a CWB Division 1 certified shop I ethically need to pretty much redesign it myself to be comfortable, and B) where the design is clear it calls for what amounts to welded moment connections (FIELD moment connections to boot w/PPJ's everywhere) for a stairwell enclosure. It's utter absurdity (looking at $30,000 to $40,000 CND PER stairwell enclosure if not more) and if I have to redesign it anyways, I might as well go fully Monty and completely change it to something that makes economical sense (as long as it's steel...dont tell me this should be wood framed...it should be wood framed but I am a steel sub lol)

Having said that I've lived a sheltered life and have never worked with cold formed steel in any significant way. But this seems like a great application for some light weight steel members if I have ever seen one (no live load, snow loads are Toronto area so relatively light). Do people think that might be a good approach to look into and if so, what are good references for design of such animals? I have to make sure I can actually design something cheaper before I submit an alternative bid!

EDIT - In case anyone was wondering we have a CofA and so can offer both design/build. Hence why I am even considering the option of just abandoning the design in hand. I'm not reckless over here!

For context here is the EOR's schematic (no loads, no conceptual framing, just a sketch of a bloody shanty)
Pic1_lnemka.png


Here is the GC's design engineer's approach to the schematic above
Pic2_gfqsxp.png


Pic3_llpsi5.png
 
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What the EOR has shown seems absurd. You could likely build the roof with 362S162-33 Rafters and Ceiling joists screwed together.
 
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And honestly a double wythe brick building new in Canada? That also seems odd.

I'm with XR, you could likely do it exactly like old wood framed raftered roofs.
 
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EDIT - Didnt notice the section XR mentioned was cold formed. Yes, I was thinking of screwing together C-sections absolutely. But do you have a design guide for such things? Even though the loads here are small and most things would work, still I've never done it before and to get comfortable I'd like to see some examples.

Jayrod I appreciate that, solid points but.....

From the OP: "(as long as it's steel...dont tell me this should be wood framed...it should be wood framed but I am a steel sub lol)"

 
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Enable - by "exactly like the old wood framed raftered roofs" I'm pretty sure jayrod is saying you can stick frame it with light gauge like you would a wood framed roof. And I would say yes - this is a perfect little shack for a light gauge back-up with veneer and light gauge roof.



 
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Aw. I am still on my first cup of coffee. My mistake!

Right, so back to does anyone have a reference to a design guide or textbook or what have you? I know it's trivial but since I've never designed with it before even just for the learning opportunity I'd like to get into something with some substance.
 
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For design guides, I use the American Iron and Steel Institute's S100 and the S200 series guides. The front of my S100 is marked "approved in Canada by the Canadian Standards Association CSA S136-07/S1-10". There's a newer version, but they got wise and stopped offering them as a free PDF.

AISI Manuals and Design Guides
 
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For CSA you're looking for CSA136 as per phamENG. In our office we also use the american standards when necessary. Often we just look at that stuff as first principles in a sense. Analyze it the same you would a wood raftered roof. But provide light gauge members with the same capacity.

I'd put my money on the contractor preferring to do a full light gauge structure with just brick veneer if you were to suggest it. If durability on the inside is a concern of the architect, provide 1/2" plywood sheathing beneath 1/2" cement board on the inside face. Might get the odd dent, but you can't put holes in the wall unless you're specifically trying to. That's what we do on our multi-tenant residential corridors to improve the durability to accidental bumps and nicks.
 
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jayrod - brilliant idea for corridors. Now I have a way to sell it when I need it for shear walls...
 
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Funny enough, that's precisely how I came up with that argument. I needed plywood shearwalls and everyone was arguing against it. Late one night that idea came to me, pitched it to the client/consultant team and it worked. So now I start with that suggestion at the beginning of the project and everyone jumps on board early. Then I have the bonus of having extremely long shear walls available to me.
 
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Wow, the proverbial brick sh!thouse in the wild. Even the architect was bright enough to anticipate light framing. Elevations are marked "top of plate".
 
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If you can compute the combined bending and compression demand in the chords, then this free software ought to help you analyze the individual members. Feel free to post your final design here for some feedback.

 
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Many thanks team. With these I was able to get a handle on what I’d like to do so I could submit an alternative bid. I suspect everything totaled it’ll come to half an order of magnitude less in cost [2thumbsup]

Will certainly be coming back if it goes through to ask questions. Lots of details that I’ll need to sort out!
 
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