Odd Stair Tread Design
Odd Stair Tread Design
(OP)
I am checking the design of a stair tread for a fabricator and am having difficulty in finding any help whatsoever. The tread is an unequal l shape bent in the shop out of A36 sheet. It has 4" downward vertical leg, 12" horizontal and is 42" long and .25" thick. A wood piece for decoration will be attached to the top by the GC. The problem is that it is supported only at the middle by a single TS. My concerns are that traditional methods of calculating the section properties and checking for bending as a cantilever member are insufficient. I asked AISC for help and they referred me to NAAMM. NAAMM responded to check with AISI. I am assuming they would respond by saying check with AISC since it is a thick member. Any thoughts would be greatly appreciated.






RE: Odd Stair Tread Design
I would think an 'I' shape that is 1/4" thick with a 4" leg should be pretty strong for a stair tread.
RE: Odd Stair Tread Design
1. For cantilever bending, consider only 4 inches of the tread and neglect the remaining 8 inches of plate (for now). Compute bending as you would for an equal leg angle, considering the buckling of the "down" leg as haynewp mentioned.
2. Separately compute the bending resistance in the remaining 8 inches of plate (as if it were just a plate tread, no "down" leg). Convert this to an equivalent load and subtract from your equal leg angle load to get the equivalent effect (after recomputing the angle bending).
3. Check for torsional bending with the tread load placed at the outside edge and inboard from the riser.
Like haynewp, I doubt there's an issue.
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design
Since it is cantilevered, I think bounciness (like a diving board) would be my concern.
RE: Odd Stair Tread Design
Another solution would be to roll a thin "I" or "S" section and then flame cut the opposing flanges off (or cut only the front edge down to the wood height), being mindful of the potential for warping.
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design
RE: Odd Stair Tread Design