roof diaphragm & shear wall connections 2

[bdlc2k]

I am designing a 50x262 icf building with cold formed/metal deck roof. Because the high aspect ratio of 5.24:1, we want to use some of the interior metal stud walls as shear walls.
Two questions are: Is this aspect ratio indeed too high to span the entire length without the interior shearwalls?
Does the interior shear wall have to reach the metal deck roof for proper transfer or can we just connect the shear wall to the chords?
I also believe that the roof can be designed as a series of simple spans.
I attached a plan for reference. Thanks!

 

[msquared48]

You will definitely need interior shear walls, and, to connect to the bottom chord of a manufactured truss, the truss will have to be rated to take the shear. Normally, I would not do that. I would install a separate wood or steel beam to connect the shear wall to, that was also connected to the roof diaphragm.

You will also have to make sure that you are not making the shear wall into a bearing wall, allowing vertical deflection to occur over the wall. Otherwise you are creating a hard point in the roof with respect to the parallel trusses, and you will work the diaphragm causing a leak, or two, or three... eventually.

Mike McCann
MMC Engineering

 

[ron9876]

If the owner will allow an interior wall I would extend it to the deck in place of a joist. If you are using ICF exterior walls and you use steel studs for the interior wall you may be introducing a trade out of sequence. The GC will likely want to install the roofing as soon as the deck is up and the interior wall framing likely happens after that. That leaves you screwing to the deck after the roofing is in place.

I also wouldn't attach a shearwall to the bottom of a joist.

 

[bdlc2k]

Thanks, for your input! Since it is a finish out, they are adding wall later, so we decided to install a chevron frame. Same basic concept, but same issue. Should the roof deck attach directly to the beam of the frame? Of course bypassing the roof joist. Thanks again

 

[ron9876]

Attach directly.