Structural Panel over 1x Lumber Sheathing Retrofit Tables??

[swooneyWOODSTRUCT]

I have been tasked with locating these tables and have not been able to find them. My boss thought they were a AWC/ANSI publication. They gave allowable load tables for 1x or 2x lumber sheathing with plywood or OSB placed over the top.

Project backstory: Designing a Timber Truss Roof with 6x6 purlins spanning the trusses, 1x decking spanning the purlins, and sheathing over the top because the values for horizontal lumber sheathing in SDPWS are so terribly low.

Any help is appreciated.

 

[XR250]

Not sure why they would be any different than standard OSB shear values. The boundary conditions would be where the issues would arise of transferring the shear into the OSB.

 

[jayrod12]

I would agree with XR. As long as you have the appropriate connections to get the shear in and out of the sheathing, then I don't see why you couldn't just use the OSB values.

 

[phamENG]

Plywood and OSB, so long as they are appropriately rated, ARE structural panels. So, yes, I agree with XR and jayrod. You found what you're looking for. Or are you trying to use some other structural panel material like gyp or concrete fiber?

 

[Craig_H]

My read is that the OP is looking for tables with combined diaphragm shear values utilizing BOTH the 1x decking and the OSB together. My experience with these types of projects is that the 1x lumber sheathing is often placed orthogonal to the purlins for aesthetic exposure below, and so I have never attempted to utilize it as a diaphragm (can't rely on horizontal lumber sheathing in Canada). Recall that the shear resistance and stiffness of sheathed diaphragms is mainly a function of the fastener (nail) resistances and stiffness. For this reason, if you wanted to utilize both the lumber sheathing and a structural wood panel (such as OSB) in combination, you would need to somehow fasten both to the supporting structure such that each has a proportionally stiff connection relative to their design resistances. I'm not really sure how one could achieve this, and it's definitely not something that I have attempted.

At least up here in Canada, there's a note addressing walls sheathed with two layers of paneling on the same side, and I believe it instructs you to only rely on the strength of the layer nearest to the structural framing. The outer layer is discounted, as its fastening to the structure is far less stiff than the other panel, resulting in it contributing very little resistance to the wall. I suspect that the same would go for diaphragms.

 

[swooneyWOODSTRUCT]

Craig_H,

You are correct. That is what I am looking for. The tables were created for retrofit applications where the horizontal lumber roof sheathing was left on the roof while structural panels (OSB or plywood) were placed on top and long fasteners were installed to penetrate into the members under the horizontal lumber sheathing.

 

[jayrod12]

Well again, as XR and I indicated, if you appropriately connect it to the boundary members, i.e. collectors, drag struts and lateral systems, then I still feel you can use the OSB values directly ignoring any contribution from the 1x decking. In a shear wall and/or diaphragm, the intermediate members (blocking, studs and joists) are only there to prevent panel buckling and I feel that the 1x decking should be adequate to prevent said buckling assuming the span of the 1x decking isn't ridiculously far.