Wood shear wall. Sheathing on both sides.

[UnneutralAxis]

I am reviewing a prototypical building/calcs for a large chain restaurant. Prototype works in most of the country, but now it's a Seismic Design Category D. In one direction of the building I only have two 4' width of shear walls for the whole direction of the building.

Question: if you place shear rated panels on both sides of a shear wall, can you effectively divide your calculated shear wall deflection in half? I am using NDS procedure for calculating deflections.

FYI, shear flow is around 900 plf to each wall. Wall height is 14'.

Thanks for the help.

 

[csd72]

I would expect that you need extra anchors at the base to get those to work.

 

[JAE]

With a tall shearwall like that, the lateral deflection at the top of the wall would be primarily due to flexure in the wall vs. shear deformation. Adding sheathing would help in that your effective flexural moment of inertia would be increased.

I'd have to look at the IBC shearwall deflection equation to see where that comes into play.

 

[UnneutralAxis]

Yes, large anchors will be required.

The prototypical calcs did not include a deflection calc for the shearwall... which I thought was pretty lazy (or just a mistake, we all make them).

After sleeping on it, a 4' shearwall is just making me nervous for these loads. I can't see it being stiff enough for this tall of a wall and this particular location. S1=.30, Ss=1.25. I'll just have to talk to the architect and figure something else out.

 

[JAE]

Under seismic - your story drift limit would probably be 0.02H = 3.36 inches.

With wood shearwalls - your R = 6 1/2 +/-. You still might be OK - just might have to use one heavy nailed shearwall system and some high strength hold downs.

 

[JoshPlumSE]

Sheathing on both sides should greatly reduce the deflection.... As far as hold downs go, I would recommend going to one of the deflection take up devices (Simpson makes an ATS system, Earthbound makes a similar device). These devices greatly reduce the deflection in the wall due to hold down deformation, sill plate crushing, and shrinkage. So, when deflection is a major issue these hold downs seem to be the preferred solution.

 

[msquared48]

Don't know if you can do it in your framing system, but if you place a beam over each 4 foot shear wall and make the length , well, say 12 feet for example, you have increased your leverage fo a factor of 3 and will be able to use smaller shearwall holddowns.

Used this trick many times.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[UnneutralAxis]

Mr. McCann,

That is a great "trick!" I have never heard of that one before, but I really like it.

 

[OldPaperMaker]

UnneutralAxis,
I don't think that you can divide the calculated deflection by 2 for sheathing on two sides of the shearwall. The deflection equation in the IBC & NDS has 4 components: bending, shear, nail slip & anchorage slip. Maybe you can change the results of one of the components but probably not the total deflection.
You might also remember that the shear value in the components is the Strength level seismic shear (not 0.7E).

Since the shearwall aspect level is greater than 2:1 (14/4=3.5) for seismic loads the unit shear capacity from the capacity tables should be multiplied by 2b/h.

 

[rscassar]

The wood code which I use allows plywood sheathing to be installed to both sides of timber framed wall as long as the hold-down requirements are doubled.