I am building an exposed deck on top of a concrete pad that is approximately 12'X11'. I'm using 2X6 treated lumber for the deck and need to elevate it in order to keep it dry. I am considering building a frame under the deck out of 1" square hollow steel or aluminum tubing with a wall thickness of .065. The tubing would be 12' lengths spaced a foot apart with the wood fastened to it perpendicular. I doubt anything or the total amount of people standing on it would be more than 500 pounds and even then not in one spot. My question is about the tubing. Is .065 a sufficient wall thickness to support the deck and weight put on it? thanks Syb

I'm not sure if this is the right forum but I thought someone here might know. I have to change the frame for a manhole cover in my house. I need to borrow some heavier duty tools to do it, in the meantime I was a thinking of just covering the hole with a piece of steel. The opening is a 20"x20" square. I'd probably get a 24" x 24" piece of metal to cover. What thickness of steel would not deform if stepped on by an adult human?