Cantilever 2nd story shear wall to 1st floor

[Disx]

Designing a conventional wood framed 2-story duplex. The client desires to have one side of the 2nd story cantilevered 2-feet over the 1st story. At the edge of the 2’ cantilever is supporting both wall and roof load. 2x12 floor joists @ 16” are facilitating the cantilever.

I have never detailed this before, but just at guess my thought is to double up the 2x12 rim and transfer the roof/2nd story shear via the floor diaphragm to the 1st story shear walls. My question and concern is how is to overcome moment/overturning?

Also, on that 2nd story cantilevered shear wall line, I have limited width for shear walls (read H:V <2). Is it possible to use something like a Simpson shear wall on a cantilever? Again, I am at the same loss as to how to transfer the chord forces.

Thanks for your help!

 

[csd72]

If you provide solid blocking between the joists over the inner wall then this will stop the joists rolling over.

The return walls can be used to help resist the push/pull at the ends.

As for the simpson shear wall, you need to go back to first principles and calculate the additional bending in the cantilever from the push/pull under overturning.

csd

 

[lsmfse]

This is done all the time. I would use at least dbl 2x12 or 4x12 @ the ends of the upper level shearwalls. Fasten/strap the end of the shearwall to dbl or 4x. Back @ the lower level walls, attach an upsidedown PHD with threaded rod thru top plates to HD post below. Agree with csd72 about the Strong-Wall.

 

[NKT]

Three ways of handling this come to mind:

1. Size the rim joist to handle the couple induced by the overturning moment in the shearwall. Calcs out best when you have a lot of short shearwalls at the cantilever. The heavy rim joist distributes the overturning forces to a lot of cantilevered floor joists which transfer the forces back to the bearing wall.

2. Install beams (or double/triple/+ joists) at the shearwall ends to transfer the loads back to the wall. Works best when you have a longer shearwalls.

3. Distribute the holdown loads to the cantilever joists under the wall according to displacement under load - zero at the approximate center of the wall and some maximum value at the ends, varying linearly in between.