Roof step w/ ribbon window

[SocklessJ]

I have a new steel building with an 8’ roof step. The wall is CFS with metal panel cladding, and runs parallel to the joists. It’s also offset from the gridline. There’s a 22’ wide ribbon window.

1. What’s the best way to support the wall? I could:

a. Bear the wall on the roof deck. I haven’t checked the deck for web crippling, but just don’t like the idea. Deck is 22ga.​

b. Add another joist under the wall and block the flutes. Seems a little weird to have two beams 14” apart, but otherwise I think this could work.​

c. Add perpendicular beams and run a gigantic bent plate to catch the wall and still get the diaphragm shear back to the gridline.​

2. Should I add HSS headers and jambs for the ribbon window, or can the cold formed engineer deal with this? I assume 22’ is too long to span a cold-formed header, but maybe he can hang it from above if I provide torsional restraint to my beam.

See snapshot below (ignore that the wall is shown extending down through the deck.)

 

[sticksandtriangles]

22' feels a bit too far for CFS, but the loads are small, so there is chance it could work.

I would be inclined to say that hanging above and either a moment clip or a diagonal kicker below might be the best solution.
Lots of times the arch will box out this area allowing the CFS to have a diagonal kicker.

 

[XR250]

If you hang it, you have no deflection accommodation above the window. And things get weird at the jambs.
22 ft. can be done with LGMF, but then you have point loads on your deck.
Not a great situation. As a former LGMF engineer, I would add the tube steel or a second beam instead of kicking this down the road.

 

[sticksandtriangles]

If you hang it, you have no deflection accommodation above the window.

I've always put a note to asking for the window supplier to provide a vertical deflection receiver at the top. Have you seen this before XR250?

 

[SocklessJ]

I guess things get weird at the jambs because they are hung from above, but the window is supported from below, right? The only way to handle that would be to hang the whole system including the window from above. Is that ever done?

Sounds like I can't get out of the second beam under the wall. That would also give me a convenient point to attach the base of HSS jamb posts.

 

[sticksandtriangles]

No jambs in the hung situation. Just add a vertical joint adjacent to the strip window.

 

[XR250]

No jambs in the hung situation. Just add a vertical joint adjacent to the strip window.

View attachment 3010

True, but the framers are going to end up screwing everything together regardless.

I've always put a note to asking for the window supplier to provide a vertical deflection receiver at the top. Have you seen this before XR250?

I have heard that but I question the effectiveness. I always try to keep things as simple as possible for the cladding folks.

 

[sticksandtriangles]

True, but the framers are going to end up screwing everything together regardless.

Damned if we ask the framers to do something complicated, damned if we spec any structural steel.

Cant win

 

[TRAK.Structural]

Back when I did commercial work tube steel would have been the solution here for me. It's not cheap, but that's the cost of this architectural feature.

 

[XR250]

Damned if we ask the framers to do something complicated, damned if we spec any structural steel.

Cant win

Well, once it gets into VE, you’ll be back with light gage steel lol.
Hopefully, you can dig your heels in