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RE: Torsion in steel stair channels

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You are correct, they are not analyzed.  Best choise would be a tube stringer.
But in reality, the treads probably afford much torsional stiffness.

We see a lot of stee stairs with steel pipe posts welded to the top flange of the stringer channel.  It is not uncommon to see a std. pipe (O.D. = 1.90") welded to and overhanging the 1.5" flange of an MC12x10.6.
Obviously, the stress in the pipe post at this point will not be developed.  How about the flange and web of the channel?  If we increase the width of the channel flange, there is now the problem of developing the torsion/bending moment in the channel flange and web.  If you take a strip of web over say 18" and try to carry the force, it will require a thick web and thus heavy channel.
Considering torsional restraint from the top flange and a portion of the web does not give much help.  How are these stringer/post assemblies analyzed?  I see such light channel stringers that I feel sure that they have not been checked except for just stair loads.
Any comments on this would be appreciated.