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We are goind to built a stair like this one:

enter image description here

But instead of two "floating" stringers, since ours will be against a wall, I thought about using plate steel and making it more flush with the wall. The fabrication is simple enough, angle iron for supports welded to the plate steel. The stringer will the be affixed at 4 points along the wall (1.5 meter intervals) like the sketch below:

enter image description here

I was thinking about using 1/8" or 1/4" plate but I'm not really sure how much plate steel could move or be "springy" in this situation. How thick should I go?

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  • Will both stringers be against a wall?
    – bib
    Commented Aug 19, 2014 at 23:55
  • No, the "floating" one will be a U profile 20x5 cm 3mm thick.
    – Luiz Borges
    Commented Aug 20, 2014 at 1:45

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Given that your stringers are going to be about 8" wide, you'll be fine with some pretty thin stuff. Heavy Jeep frames from the 1970s were only about 3/16" thick, and only about 4" wide. I've seen truck frames around 1/4" by 8", but they were larger single-axle agricultural trucks. Really large single-axle trucks only have about 1/2"-thick steel frames.

Come to think of it, I've walked stairs made with no heavier than 3/16" stringers in penitentiaries. They felt nearly like STONE.

If you're concerned about racking, remember that every tread will act as an anti-rack brace. Until your treads go on, the stringers will feel pretty flimsy if you push them sideways. AFTER the treads go on, they'll be train-wreck rigid.

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  • So, considering that the other stringer will be a U profile about 8x2" 1/8" thick, what you recommend for the flat stock one: 1/8, 3/16?
    – Luiz Borges
    Commented Aug 20, 2014 at 1:47
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    I'd think that 1/8"x8" plate stock, anchored to the wall in four places, should be enough to drive horses up & down. Make GOOD fillets on the angle iron, and jig-weld like crazy. Any slight imperfection will be felt by a person climbing the stairs. In fact... jig-weld ONE stringer, then use THAT as a jig to weld the other one - clamp their angle irons together for positive registration, tack-weld all at once, then finish-weld them all. GOOD fillets, GOOD penetration. You never want any of those welds to fail.
    – TDHofstetter
    Commented Aug 20, 2014 at 1:56
  • Thanks for the tips, one final doubt, do you think it is doable to have both stringers be made from flat plate, without "wings" like an U profile for reinforcement. After your encoragement I'm thinking on going for a more clean design, maybe using a thicker plate just for the looks.
    – Luiz Borges
    Commented Aug 20, 2014 at 2:30
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    I think that outer stringer should probably be a u-profile instead of a flat - the upper & lower legs add stiffness in all dimensions. I doubt you'll NEED any of that extra stiffness, but I'm a strong believer in applying "safety factors". Like... what if six giant guys move a piano up those stairs someday? I try to always build things that're guaranteed to hold up to ANYTHING that ANYONE ever does, long after I've had my dirt dinner.
    – TDHofstetter
    Commented Aug 20, 2014 at 2:57
  • I found the following document about flat stringers, they explain what you just told me. I think that I probably could work with 2 flat stringers, but I would then use 1/4" stock. But stiffness is important, I think that without an U profile I could have too much vibration when walking up the stairs. steelconstruction.org/…
    – Luiz Borges
    Commented Aug 20, 2014 at 3:35

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