The torsion box is a handy way to create a thick panel with the strength to span a large area. Because the panel is mostly hollow, it also is very light. It can also maintain its flatness and not flex under stress.
The secret is in the core. Everyone has seen the concept in the making of hollow core doors. The core is mostly made with cardboard and the doors don't really have to lay horizontally and support a lot of weight. However, if you want to make a table or roof where strength is an issue, then try this idea and make a torsion box of your own.
The system requires three components, a core grid with a layer on top and a layer on the bottom. Sounds simple and is. In this project I used 1/2 in plywood for the grid with 1/4 ply for the top and bottom layers. In the choice of materials, the factors of strength, length and lightness dictate.
Make the grid by cutting long strips and then filling in the cross pieces with short cut-offs, or make continuous crossing strips and notch them to fit together, finger joint style. Smaller grids make the panel heavier and larger grids are more open and make a lighter panel. Make the outside pieces of the whole frame, out of thicker material.
The flat spots are where table legs will be added.
This torsion box, covered with stainless, makes a generous work station.
The central horizontal has to span a five foot wide TV and support the top cabinets.
The two projects I've shown here are first a bakery table covered with stainless steel and secondly a cabinet for a huge TV. Both utilize a torsion box for horizontal strength.