floating stair

huangyhg

floating stair
i'm designing a floating stair with cold rolled steps, wall concrete-mounted. section is 305x80x25x2.0mm ("c section") and the cantiliver span is 160mm. figures are ok but now in building work the section is twisting and deflecting. what could i do?. how could i design properly these elements?   
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how many and where are the stringers?
please explain what you mean by "floating stair".  and i take it the 305 dimension is the tread width and the section is 2 mm thick, but what do the 80 and 25 dimensions represent?  you say the tread cantilevers 160, but how far does it span?  what supports the treads and how are the treads connected?
thanks for your interest. i'm sending files with details.
regards,
  
i would have used a closed section for the treads - channels are not torsionally stiff enough.  can you box in the bottoms of the stairs?
yes, i can add a plate at bottom. buy how can i check the section?
i can't open the files.  maybe someone can tell me how to do it.
is the cantilever 1600mm?
why don't you start off by stating what part of the aisc steel code you used to arrive at the shape you chose. also state how you found the torsion on your shape and what equations from the code you used to choose your shape. this will most likely reveal your error.