Cantilever Wood Diaphragm (W' +100')

[EngStuff]

I have a wood structure that has walls on 3 sides, I am designing it as a cantilever "Open Front Structure", it's open without any store front windows at the front end, so it's a partially enclosed structure. I usually do these by hand, but for this particular one, I wonder if the dimensions are "too long" and/or i should take into account that the portal frames will take some of the loading due to the structure rotating or if I could ignore the portal frames for that loading. (Refer to image below)

My L'= 20 feet, my W'=100+ feet from out to out, So it definitely meets the L'/W' ratio of .67. I do have portal frames in-between to resist the wind load from the direction perpendicular to the W' (long span).

I wonder if having a large W' could be "too Large" I don't see any limitations on the SDPWS 2015 addition.

Should I assume that the portal frames will take some of the wind load perpendicular to the L' direction, because the structure is too long and it will rotate slightly, or could I get away with assuming "no portal frames" when designing for wind perpendicular to L' and only wind loads the portal frames see is wind perpendicular to W'?

I have seen many questions that involve Cantilever diaphragms on here, but not involving my situation.

 

[driftLimiter]

Perhaps if you treat the diaphragm as rigid and use the relative stiffnesses of the frames vs. the walls you could get a decent result. I can't think of how one would analyze the forces in the intermediate frames using a flexible diaphragm approach.

 

[ChorasDen]

Eng, what's the unfactored wind PLF load on the L side? Let me run it through some software assuming no portal frames and we can see how it performs.

 

[jittles]

W getting larger (and the aspect ratio smaller) is surely better, hence no limitations in the SPDWS...

I'd say it's fair and code-compliant to ignore the portal frames.

But if I were doing it myself I would likely envelope some portion of load to the portal frames.

 

[ChorasDen]

Note sure the portal frames would even be necessary for loading perpendicular to the L direction. Assuming continuous shear walls on the top and sides of the diaphragm, the system would be so stiff that you wouldn't need them, and since we are assuming rigid diaphragm, how much load would actually make it's way to the portal frames?