I'm building a platform 22.5-23.5" high in a space 88" by 62-64", supports on three side but one free span side for a bed to slide out - the long side, of course. Because of height/width restrictions, space is at a premium, and wood just takes up too much room. I'm looking to save inches and weight wherever possible, but still end up with a platform that is structurally sound with minimal deflection (i.e. 50+psf live load, less than 1/3" deflection across long span).
Various online calculators go back and forth on whether I can use 2x2 steel or need 2x3 steel at 1/4" thick, or whether aluminum at 2x3, 1/4" would suffice. Will 2x2 steel work or 2x3 aluminum? Or stick with steel 2x3, with the long side vertical?
For either steel or aluminum: do I just use another length of same dimensions at sides for beam, and what kind of posts? For welding, as long as it is in the same plane, I don't 'pay' (in height or width, the most restrictive measurements) for extra lateral or bracing support on the platform top; besides corner triangular braces, should I add short lengths between metal joists for more support?
And, finally, how do I attach a plywood subfloor to the top of this frame? Are there brackets that go around 2x3 (or 2x2) that would work?