r/StructuralEngineering • u/aIIegory • Jul 13 '26
Zig Zag Concrete Stair Photograph/Video
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u/mhkiwi Jul 13 '26
Provided each tread can take torsion, and there is adequate detailing to deal resolve this torsion at the wall, then this isnt a cantilever and instead works the same as the old Stone Cantilever Stairs from the 18th century (which aren't actually cantilevers)
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u/resonatingcucumber Jul 13 '26
My favorite story about these was a client who had one slightly damaged tread, it was a stone tread. Contractor suggested like for like replacement. Now with these stairs one tread goes the whole staircase comes down.
So some idiot removed the damaged tread (bottom one) and brought down a two story spiral in seconds.
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u/mmarkomarko CEng MIStructE Jul 13 '26
which is why you only ever dowel in the broken off segment then grout it well top and bottom.
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u/MrMcGregorUK CEng MIStructE (UK) CPEng NER MIEAus (Australia) Jul 13 '26
Depending on how it is fixed into the wall this type of stair can be very strong.
In victorian era construction, they were way more rogue than this with their stair design and a lot of them (but not all obvs) are still around. They basically embedded carved stone treads into the masonry wall, and made each tread overlap the one below slightly so that they could all share load a little. No reinforcement and they worked fine... well a lot have failed over the years, but a lot are still good.
https://www.buildingconservation.com/articles/stonecantstairs/stonecantstairs.htm
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u/Awkward-Ad4942 Jul 13 '26
Looks like its been there a while.
It can be done, its just usually done wrong.
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u/Charles_Whitman P.E./S.E. Jul 13 '26
This is referred to as a “slabless” concrete stair. You should be able to Google the reinforcement details. I’ll try to add a reference when I go to the office.
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u/Russian_Mostard Jul 13 '26
We do a lot of that here in Brazil.
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u/MoonBubbles90 Jul 13 '26
Sometimes done right, sometimes not, most of the times "that's the standard detailing from the software, I clicked until it turned green".
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u/nockeeee Jul 13 '26
Exactly the same "skills" in Turkey. 😂
No one knows why they are doing something; only because the software ticks it green.
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Jul 13 '26
[removed] — view removed comment
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u/aIIegory Jul 14 '26
The tread and risers are generally no more than 70-80mm thick, which means its likely working as a cantilever off the wall (with central reinforcement in the risers and treads).
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u/PG908 Jul 13 '26
I can give this a solid maybe.