Cantilever Steel Deck Diaghragm
Cantilever Steel Deck Diaghragm
(OP)
I'm designing a small attachment (single level, ~900 sf) to an existing steel building To save on bracing, I'd like to design the roof diaphragm as a cantilever (see attached sketch - traditional method on left, proposed method on right). I can see no good reason this wouldn't work, and it would basically eliminate the need for bracing this addition, but it's also something I've never done. Some background - wind loads will control, seismic loads are an afterthought where I am and will be much smaller than the wind loads on this structure. No significant gravity loads on the roof outside of snow.






RE: Cantilever Steel Deck Diaghragm
1) Deflection of the diaphragm at the free end.
2) Diaphragm aspect ratios limits expressed in the governing code.
Expect many of our cohorts to dislike this from a seismic design perspective.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cantilever Steel Deck Diaghragm
Mike McCann, PE, SE (WA)
RE: Cantilever Steel Deck Diaghragm
RE: Cantilever Steel Deck Diaghragm
@ms - I'll certainly be checking it, but it frames into a 180' tall 80x80 braced frame building. So unlikely to need any reinforcement
@lion- tying into an existing braced building, not a diaphragm. Otherwise it would be a whole different ball game
RE: Cantilever Steel Deck Diaghragm
Assuming a rigid diaphragm, I don't think that I'd have any concerns.
With the more typical metal deck/flexible diaphragm, you need to keep a close eye on deflections along the right hand side - including both shear and flexural deformations.