Cold Formed Steel Stage

[Bammer25]

Have a client wanting a cold formed steel stage in a commercial building. No wood for fire protection reasons. Anyway, I don't do a ton of work with this stuff. No seismic or wind so very straight forward, but my question is about the detailing. The stage will be semi-circular in plan view. Can you get curved pieces, or would I be looking at cantilevering beams off slightly in increasing lengths and having some sort of banding that goes around the edges?

This will be very lightly loaded.

Also they want a wheel chair ramp attached. I have done wooden wheelchair ramps where you can rip members to get your slope just right. Any pointers?

 

[ANE91]

I have worked in factories that assemble the roll-form machines which produce CFS members. I am unaware of of any that do curves, though they may exist. What I typically see is a curve discretized using many short, straight pieces.

Ramp should be no problem. You can probably buy it pre-cut/kitted, or at least be able to cut and screw as-needed in the field.

I have no substantive CFS design experience to offer. That said, and while the "no wind" thing makes sense, the "no seismic" thing gives me pause. I doubt that your local code allows you to ignore seismic detailing completely, even in SDC A.

 

[phamENG]

Clark Dietrich makes a curved track, but it's marketed as non-bearing and for drywall studs only. It's a bunch of little pieces of track riveted (or something) together so they articulate into all sorts of curves. Probably need to cantilever out to something like that and use it to make a 'non-bearing' curtain wall. Or discretize the curve as ANE91 mentioned.

 

[JAE]

We typically delegate the design of cold formed framing and walls - there are several companies that specialize in this.

Having said that I have done some design and detailing of LG framing. Takes some time and study so if your fee is tight maybe consider delegating.

Agree with ANE91 on seismic. (except SDC A doesn't require seismic "detailing" - only application of a nominal load.)

You say lightly loaded but then add a wheelchair ramp and call it a stage. This suggests 100 psf or more loading per ASCE 7 in the US.

 

[JAE]

For the knife edge of the ramp at the bottom we've sometimes constructed a concrete toe to the ramp (using a slab depression of 1 1/2" or more and extending the concrete "toe" up far enough where there's then adequate depth to start the LG steel framing from there.

 

[Celt83]

For curves generally do a cantilevered LG joist portion with infill wall below to either a field knipped track to create the curve or one of the pre-fab curved tracks.

You will have nominal seismic loading as others have mentioned. We typically put some notional lateral live load to account for inertia of people moving and stopping/changing direction. Agree with @JAE regarding 100 psf live load.

We've been using FRT plywood for the top surface to satisfy the non-combustible material requirement, type 3 wood construction has made it easy to source. Make sure your LG knee walls are braced in two directions we accomplish this with LG in-plane bracing and out-of-plane "X" bracing (around 48" o.c.).