Bearing Strength of Plywood

[BSVBD]

NDS Table 11.3.2B provides Dowel Bearing Strength of Plywood.

I have always considered that this would be for plywood fastened to dimension lumber with the nail or screw head on the side of the plywood.

Due to inaccessibility, if we cannot fasten to the plywood from the plywood side, can we still use these same load values, to transfer load FROM the plywood TO the dimension lumber if we fasten FROM the dimension lumber side, having the nail or screw head on the dimension lumber side and the point of the nail or screw penetrating out of the plywood?

Does this make sense?

Thank you!

 

[jayrod12]

I'd have to look, but I swear in the Canadian code it strictly forbids this for nails.

 

[BSVBD]

What, then, is your opinion for threaded fasteners?

 

[MotorCity]

Considering bearing only, the screw doesn't "know" which side of the plywood it is installed from so the bearing strength should not be affected. Now, if you look at the different failure modes of a fastener, the order of attachment of the various plies may affect the strength.

 

[mike20793]

It gets done on truss repairs all the time. It's quite common to call for double plywood gussets with 16d nails fully clinched. There are specific guidelines for the proper clinching of nails.

 

[BSVBD]

I'm surprised that plywood has considerably greater bearing or compression strength than that of dimension lumber. For example, SPF #2 has a compression parallel of 1,150 psi. How does plywood obtain 3,350 psi?

Am i understanding this correctly?

 

[jayrod12]

For threaded fasteners I'd be a little more lenient, e.g. simpson A35 clips.

mike, for truss repairs with clinched nails, that means you can get to the other side to clinch them, in BSVBD's case, I assume they can't get to the face of the plywood otherwise they would install the fastener's correctly.

 

[BSVBD]

MotorCity... due to the flared head of the fastener, the plywood would be laterally braced against the member it is being connected to, thus providing the secure connection to which the Table 11.3.2B and other dowel-type fastener load tables MAY be base upon. Any further thoughts?

Mike... what is "clinching".

jayrod... base on what you said regarding Canadian code, i am considering not using nails. However, I wonder why NDS says "Dowel Bearing", and then, in the paragraph below the Table, provides a commentary specification "For" threaded full body fasteners.

The opening word "For" leads me to believe that the lower paragraph is exclusive to those threaded full body fasteners. Therefore, NOT exclusive to the threaded full body fasteners, ALL dowel-type fasteners, including nails, should be included in this table.

Comments?

 

[BSVBD]

Please see "Bearing Strength of Plywood - 2" for another aspect of inquiry related to this post.

Thank you!

 

[MotorCity]

BSVBD,
The plywood wood be laterally braced against the member regardless of which side the screw is installed from. Say you install the screw such that it goes all the way through the plywood and the main member. If you were to cut a section through the assembly, the only way you could tell which side the screw was installed from would be by observing the direction of the threads.
I don't have that table in front of me at the moment, but be careful with your terminology and the terminology used in the tables (screws vs. dowels)
Is this for a shear wall? In my experience bearing usually does not control.

 

[BSVBD]

MotorCity... are not nail, screws and bolts all considered dowel-type fasteners?

That is what is stated in NDS Tables 11A-R.

In addition, although NDS Table 11.3.2B provides a Dowel Bearing Strength for Plywood of 3,350 psi, I consider that a #8 screw (for example) may not be able to support 329 LBS that the calculation equates to. [0.131" x .75" (plywood) x 3,350 psi]

Am i missing something, over analyzing or just wrong!

 

[MotorCity]

BSVBD, sorry you are correct with the definition of dowel (I was thinking one thing and typing something else, its a friday)