load spread through plywood

[civil_4343]

There is a temporary concentrated load on 3" of plywood on top of a concrete roof slab. How much will the load spread through the plywood? Is the spread 1:2, 1:1? Is there a reference for the spread of a concentrated load through plywood?

 

[jayrod12]

I would argue you'll get at best 2V:1H, the wood will essentially just act as a squishy blocking when compared to the concrete slab.

 

[phamENG]

I agree with jayrod. If you need more, use a heavier timber mat - maybe two layers of 6x6s at 90 degrees to one another. The concrete is likely going to be a lot stiffer than the cribbing, so you need a lot of cribbing to make it spread much beyond the footprint of the original load.

 

[Ron247]

I agree with the 2V:1H with only adding to that the width of whatever applies the force. The slope of the load path starts at the edge of the applied load assuming the application material is stronger than plywood.

Also, I saw a plywood spacer years ago that had a repeating load on it. The area had some ponded water on it. Each time the load passed over it, an isolated area squeezed more water out than the adjacent area. It was about that same as the 2:1 cited here. The plywood was old but it appeared to be pressure treated so I assume it was similar to pine. Oak may be a little stiffer but I would not rely on that.