trying to design a straight stair run using steel tubes as stringers. total run = 10'-0". total rise is 8'-8", width 3'-0". Support is only at each end. yes these are steeper than normal, and do not access a living space. would two steel tube 5"x2" x 1/4" thick be stiff enough? if not what size rectangular tube would be required?
Yes, two 5” x 2” x 1/4” steel tube stringers (with A36 steel) spanning 10’ will adequately support your stairway.
Code requires a Live Load of between 40 lbs. per square foot (psf) and 100 psf depending where it’s located. Assuming it’s 100psf x 3’ wide x 10 long = 3,000 lbs. plus a Dead Load of 15 psf x 3’ x 10’ = 450 lbs. for a Total load of 3,450 lbs.
Your tubes will support about 8,000 lbs. each, depending on connections, etc.
If you don’t have the tubes already, you may want to consider a 5” x 1 3/4” channel which will support 5,100 lbs. each.
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If steel is magnetic it pretty much passes A 36 requirements ,so I would not worry about steel specification. – blacksmith37 Nov 2 '20 at 15:14
