LD1
Epic Contributor
I wouldnt use that as an example to try and illustrate the strength of plywood.Not germane to build up beams...but an example of the strength of plywood etc...is in the form of engineered wood joists...i.e., TJIs by Weyerhaeuser...
They basically consist of a piece of plywood or OSB etc. typically ripped to 8", 10" or 12" (sized to match common lumber dimensions) with a solid wood rail at the top and bottom...the load bearing capabilities typically surpass the strength of solid lumber joist etc...
A beam of any kind......the key to strength is in the extreme most fibers. The top edge of a beam in compress and the bottom edge is in tension. The more "mass" and material you have at the edges the stronger it is a resisting deflection. And all the material in the middle is just there to keep those extreme edges separated.
Thats why the I-beam is such a popular design. IT concentrates ALOT of material where it matters most.
Same is true for those I-joists like you describe. If you had a I-joist built up with a 2x6 or 2x8 in place of the OSB it would fare equally as well. They use OSB because it is cheaper, and only acting to keep the 2x4's on the top and bottom separated. So its strength isnt critical.
You can also compare floor "trusses". Where the strength is in the top and bottom.....and the middle is mostly just air....lol