Mono stringer staircase problem

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subseaengineer

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Hello friends, I projected an staircase using a W section beam (W150x13 kg/m), web and flanges about 3/16" thick. It uses a central beam as support with steel steps which will receive a larger wood step later.

It's doesn't move close to the places where it's bolted on.


Some pictures and videos of the stair below.

The stair is strong enough except for the side torsion. I did not plan that... What are some ideas to solve? I have some, could you guys help? I am not an structural engineer.

Close both sides from end to end with weld, creating something like a rectangular pipe.

Other idea is to use a molded channel to the exact size to fill the inside of the beam, reinforcing the web and flanges.

View attachment PXL_20210615_192210614.mp4 PXL_20210618_180333978.jpg
 

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leggo PE

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I think you could try adding stiffener plates at each side of the beam flange at the location of each step. That should stiffen up the section, as from the video (super helpful, thanks for posting!) it indeed looks like the single stringer beam is what is twisting when load is applied.
 

subseaengineer

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I tried this on the first two steps, it still happened, I could do it the entire length, but I do not think it will work as desired.

I made a drawing of the two ideas I have.

The first will turn the section in a Box with a web.

The second will stiffen the existing flanges and web.
PXL_20210624_040345966~2.jpg
 

KevinChez

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*** the video just loaded so that answers my questions:

where is the movement? in the tread, the top flange, or beam twist @ the stringer? or all three?

is the movement so great that is makes it feel unstable? I would expect some movement or shake.

I would add a web stiffener on each side at the tread. Do you have a full moment connections at the ends? That may help too. If you connections are moving you may want to try an achieve a fixed/semi fixed condition. adding a web stiffener on the back side of the support beam on the wall may help as well.
 
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