Long Shear Wall

[dgengineering]

Hi everyone,

I am designing a 2 story house with a balloon framed stairway 23' high. The wall there is 4.5' so if I design it as a shear wall it exceeds the 3.5 ratio. I know it should have a lateral system but what can I use? Maybe hardy frames stacked together? Please help me with this.

Thank you

 

[jayrod12]

Stacking frames sounds like a terrible idea. what will brace them?

That being said, a sketch of the situation usually will help immensely with getting constructive advice.

Are there not other walls that aren't 23 feet tall and only 4 1/2 feet wide that you can use as shear walls?

 

[dgengineering]

no, there aren't any other walls on that line. I will attach a sketch

 

[dgengineering]

here is the PDF of floor plan and elevations

 

[jayrod12]

That's a bit unfortunate.

Is it possible to design a wind girt at roughly mid-height of the wall that is stiff enough/strong enough to provide lateral support for the shear walls? Then you could consider it two walls that are each roughly 12 feet tall. Then you should be within your 3.5:1 ratio.

 

[JAE]

Why can't you rely on the set-back adjacent wall (with window) to be the shear wall and cantilever out your stairway with floor-level beams extending out to brace your long thin wall?

 

[dgengineering]

Why can't you rely on the set-back adjacent wall (with window) to be the shear wall and cantilever out your stairway with floor-level beams extending out to brace your long thin wall?

how would that work? please explain more

 

[dgengineering]

the other wall is already a shear wall

 

[JAE]

Something like this - assuming you can get the adjacent shear walls (SW) to work.

 

[dgengineering]

Thank you for taking the time to sketch it. But what's supporting the collector? a beam in the middle of the stairway? I'm assuming you meant a post at that support (first support from left). Correct?

 

[JAE]

"But what's supporting the collector? "
The collector is a member stretching along the whole exterior wall that "collects" horizontal shear forces and delivers them to shear walls.
It would be supported vertically by the underlying stair wall or the red beam and by the exterior wall beyond the stair.
This collector would essentially stretch from the stair wall to the corner of your building with the main floor diaphragm to the right of it.

In my sketch, the collector provides horizontal support at the point on your cantilevered beam that extends outward. The other horizontal support would be further inward and resisted by interior floor framing tied into the main diaphragm.

Any lateral wind forces on the protruding stair bump-out would be resisted by the cantilever and that force sent into the collector that would stretch out to your building corner and deliver that load down into the two blue shear walls.