shearwall

[hello12345hello]

I have two story wood shear wall. Upper story wall is 12ft wide and lower story is 9ft wide with 3ft opening at the end. To check overturning can i still use 12ft wall with proper uplift connector at lower story. I will use 9ft wall only for shear capacity.

 

[JAE]

Yes - just be sure to extend the end posts from the upper wall down to the lower wall by tying the posts together for tension via straps or some other connection method.

 

[jdgengineer]

I don't think you would want to use 12ft for the overall assembly. Use the 12' length for the upper wall and the 9' length for the lower wall. You would then have three holdowns one on either side of the opening and one on the other side of the wall. The stacked post would be designed for the combined overturning while the other two posts would just have their individual uplift.

Alternatively, you could look at a force transfer around opening or similar methodology but you will need at least 2' of wall on either side of the opening which it doesn't sound like you have.

 

[hello12345hello]

so here try to understand what is tension at lower story than. see attachment.

 

[msquared48]

JAE:

Actually, I will have to disagree here unless there is a twelve foot transfer beam at the second floor that is to act as a transfer beam to resist a lifting force from the interior end of the 9 foot shearwall. Without that, which is probably the case, you are looking at three holddowns - probably different sizes.

One at each end of the 12 foot shearwall, extending the overturning forces from just the 12 foot wall to the foundation, and "two" effectively for the 9 foot shearwall. The portion of the 9 foot wall that aligns with the end of the 12 foot wall will see the sum of the overturning forces for that holddown. The other end of the 9 foot wall will only see overturning from the 9 foot wall. Hence three holddowns.

If the descrtiption is too confusing, I can post a sketch.



Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

As a corollary here, another option for using only two holddowns besides the solid stick transfer beam at the floor level, would be to make the 12 foot long shearwall function as a plywood deep beam. However, above the interior end of the 9 foot wall, additional stud reinforcing would have to be placed to act as a column for the uplift from the 9 foot wall to transfer to the 12 foot wall.

Other than those options - three holddowns are needed.

Have I confused anyone yet?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

Why not just use the shear wall as 9' long and ignore the 3' part on the upper floor?

 

[JAE]

The natural "inclination" of the upper, wider, 12 ft. wall will be to overturn and pull up the outer sections of the wall. I think that because of this you do need, or want, to use the outer edges of the 12 ft. wall to place a hold down - extending down through the lower wall.

I'd agree with Mike, in fact after posting I did think of this, that there ought to be a hold down at the end of the lower, 9 ft. wall of course -but also perhaps extend it up through the 12 ft. wall as well.

If you ignored the upper 3 ft. extension, hokie, I would worry that without the extension the 12 ft end post down to the footing, then you'd get a distress, tear, cracking, in that 3 ft. extension as it would stretch out or move much further.

 

[woodman88]

I would go with three holdowns.
I would not strap the lower wall to the upper wall and the door opening unless you are going to design the upper wall (strap and lower holdown) for only 9' length of shear.
As for distress, etc. for a major code event this is going to occur architecturally throughout the structure and over connecting the structure will not reduce the cost much IMHO for the work that will be needed.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

Hokie's solution is the simplest, but would mean slightly larger holddown capacities would be required.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[timbercharlie]

I agree with hokie66... just stack two 9' shear walls.