keyPitsimplE
Structural
I have searched high and low for allowable concentrated loads on plywood of various thickness and joist spacing. Anyone know of such an animal?
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Concentrated Loads on Plywood 1
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Not specifically.
The APA (American Plywood Asssociation) has a specification that provides allowable stresses in plywood - both for stresses in the plane of the sheet and across the plane.
Most codes like IBC provide maximum spans based on uniform loads but that is not what you are looking for.
The only way I know to check plywood for a concentrated load on a span of plywood would be to get the APA specification and use basic statics, analysis, etc. to determine shears and moments in the plywood - get the stresses - and then check against the APA allowable stresses.
I got the attachment below from
The APA (American Plywood Asssociation) has a specification that provides allowable stresses in plywood - both for stresses in the plane of the sheet and across the plane.
Most codes like IBC provide maximum spans based on uniform loads but that is not what you are looking for.
The only way I know to check plywood for a concentrated load on a span of plywood would be to get the APA specification and use basic statics, analysis, etc. to determine shears and moments in the plywood - get the stresses - and then check against the APA allowable stresses.
I got the attachment below from
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keyPitsimplE
Structural
As far as I can tell, that would be a 3D analysis. Not sure of a simple, accurate way to simplify that. Even a 12" wide flat "beam" of plywood taking the point load would be too conservative. Maybe 24"? Some tested values would really be nice for deflection, punching shear, etc.
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keyPitsimplE
Structural
I spoke with APA's Technical Svcs. Div. and got an answer, but I'm not too convinced it is appropriate. The rep. claimed he checked it with his manager who is a P.E., but the document provided does not describe this as a method of determining punching shear.
Perimeter of point load X Fvtv = Punching Shear Capacity
F sub v t sub v is the "Panel Shear Through The Thickness" value listed on Page 21, Table 4B in APA's 28 page "Panel Design Specification" dated 2008. The document he sent me was D510.pdf. It is also listed with respect to span rating on pg. 18, Table 4A. Table 4B gave the most conservative value based on thickness of 105 vs. 115 on Table 4A.
So for my floor with a 4"x4" square point load on 23/32" AC plywood the value is 16 in x 105 lb/in = 1680 lb! I assume this is for the max. support spacing of 24" since the product is rated 48/24. My joists are 16" o.c.
Other load cases such as bending and deflection certainly control this design. I guess this calc would be most applicable for small footprints like a 1" square.
Perimeter of point load X Fvtv = Punching Shear Capacity
F sub v t sub v is the "Panel Shear Through The Thickness" value listed on Page 21, Table 4B in APA's 28 page "Panel Design Specification" dated 2008. The document he sent me was D510.pdf. It is also listed with respect to span rating on pg. 18, Table 4A. Table 4B gave the most conservative value based on thickness of 105 vs. 115 on Table 4A.
So for my floor with a 4"x4" square point load on 23/32" AC plywood the value is 16 in x 105 lb/in = 1680 lb! I assume this is for the max. support spacing of 24" since the product is rated 48/24. My joists are 16" o.c.
Other load cases such as bending and deflection certainly control this design. I guess this calc would be most applicable for small footprints like a 1" square.
MiketheEngineer
Structural
APA is the authority - They had a book out a few years ago that did a pretty good job of explaining this. Had to do with heavily loaded wheel loads - similiar to what I think you are looking for. Check their site again
The attached table shows ultimate strength of plywood under a concentrated load. Unfortunately, this is the only sheet I have from the publication. I believe this was published at least 25 years ago by APA, and was titled Research Report 135 "Plywood Composite Panels for Floors and Roofs." I've tried to find the entire report, without success.
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keyPitsimplE
Structural
Thanks, meicz. That at least gives me something to compare against. I think I would probably use the average ultimate load divided by 3 for an approx. allowable load.
To complete this post, I'll attach the document I was referring to above.
To complete this post, I'll attach the document I was referring to above.
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keyPitsimplE
Structural
I just noticed that JAE posted the same attachment I did. This looks like the best resource available.
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