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shearwall sheathing orientation- weak axis bending

shearwall sheathing orientation- weak axis bending

shearwall sheathing orientation- weak axis bending

I am looking at using 24" stud spacing on a project... for the first time.... (its energy related... hehehe)
So I have been looking into the out of plane capacity of the sheathing... to make sure thats not an issue.

Typical details I adopted, show the plywood orientation installed vertically. This is generally a more cost effective way to build. But, it also makes it difficult to determine the minimum sheathing thickness. All span ratings I have found, are assuming strong axis bending.

And so, I am re-inventing the wheel... and looking at a few characteristics of the typical details I adopted:

It is my understanding, that running the plywood vertically can eliminate the horizontal joints, and/or lends itself to staggering the horizontal joints. Both of these things, increase the stiffness in plane. (I wouldnt be surprised, if it also increased shear... although I found no difference in the code.) Can anyone point to a good document on this? (any document on the increase in shear capacity would be good too)

It is also my understanding that Structural 1 Grade has increased cross bending performance, and better racking. Can anyone point to a good document on this? Something with substance (numbers even)... for instance; how that increased racking resistance increases capacity... or, does the increased cross bending capacity, increase weak axis span capacity?

But primarily, I am looking for a way to determine weak axis capacity.... so I can be sure that a 24" spaced supports wont exceed the deflection limits or the stress limits....
meanwhile, Ill be checking the studs...

RE: shearwall sheathing orientation- weak axis bending

Sheathing weak axis capacity: SDPWS 2015 table 3.2.1
More in-depth sheathing properties, but careful, this stuff is confusing even for wood engineers: Engineered Wood Association Form No. D510E, Panel Design Specification 2020
Shear wall values are the same in both cases, panels vertical or panels horizontal: SDPWS 2015 table 4.3A

RE: shearwall sheathing orientation- weak axis bending

Mike Mike, thank you. This is great. I never would have thought to look in the SDPWS. And, thanks for the APA document reference. I thought I searched the whole site.... never found this one. And youre right, this document will take some time. Time, I dont really have.

Are you aware of anything else that deals with deflection? I'm hoping for a table tat gives the minimum thickness for use with brittle finishes? Plaster finishes.. flexible finishes...?

I know the code gives a value for either vertical or horizontal orientation. But just as an aside, I did come across some documentation, saying the vertical orientation, with staggered horizontal joints, was stiffer. And, the whole basis for diaphragm shear values is based on panel orientation..... so, I believe the staggered horizontal joint yields better shear values. This same document, had the table I need for out of plane deflection for brittle finishes.... but I cannot find it again. If I recall, for around 35psf wind, weak axis, 24" stud spacing... 5/8" plywood... but Im not sure I do recall correctly. Again, just as an aside.


RE: shearwall sheathing orientation- weak axis bending

Let me know if you find it. Deflection is a concern and it appears SDPWS table 3.2.1 doesn't seem to address it. 5/8" plywood on 24" OC studs feels just thick enough to me, although it would be nice to back it up with some numbers. What happens if you calculate the deflection on 19/32" 40/20 5-ply plywood with EI = 250,000 lb-in2/ft and compare it to IBC wall deflection limits?

RE: shearwall sheathing orientation- weak axis bending

Mike Mike,
I found a lot of good info. Unfortunately, nothing that addresses my specific set of circumstances directly. There is an APA table for weak axis bending for walls, for L/120, and another for stucco at L/360. Nothing in between. And again, 5/8" min thickness for weak axis, with stucco/plaster.

I design all my walls for deflections allowed for use with brittle finishes...... at a minimum. And who uses L/120? But, I didnt want to use 5/8" unless I had to...... so I kept looking.

Two things I did find:
1. Weyerhaeuser has engineered plywood, with strong axis in the 4ft direction... designed specifically for walls. Which I think is very cool.
2. I found a table in the code for roof ply, weak axis bending.

I used the code tables, and 1/2" appears to work.... but its close. So, I am thinking of also specifying the plywood with strength axis in the 4ft direction... I want to see how hard it is to get anyway... if its more expensive, if Struct 1 available, etc...... and this client will use Weyerhaeuser anyway.

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