Torsion box

[billd6]

I'm building a 30 x 72 inch torsion box out of plywood that will span a distance of approximately 3 feet. I'll be using a grid of 1 inch high pieces of plywood in between the two sheets. The box will have to support a weight of approximately 150 pounds. Does anyone have any experience building one of these things? Can I use half-inch plywood for the 2 sheets or do I need to use three-quarter inch?

 

[zkling]

Sounds like you are going about it the wrong way. For a torsion box, you want taller riseres (making the box thicker) and use thinner sheet to skin it. The skin only needs to be thick enough to resist penetration which will be determined by the riser spacing. The wider the ribs are apart, for a given load, the thicker the skin needs to be. I'd suggest you look up a few plans, there are a ton out there. That would give you a good basis to design off of.