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Re: Curved Stair

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At 10:52 AM 06/02/2000 -0500, you wrote:
>    <<  Forget using a channel. Torsion will kill you on a curved stair. >>
>
>Then I wonder why so many monumental curved stairs have been successfully
>designed and fabricated with channel stringers?  Maybe it is like the plight
>of the poor bumblebee.  

Last item first: Plight of the Bumblebee is flayed on the fiano.

Channel Stringers: They're common with aluminum and fiberglass extension
ladders, and have inadequate torsional stiffness for stability as straight
beams on the long spans the ladders extend to. But note that the rungs
attach with moment-resisting connections to the channel stringers. With the
two stringers set a fair distance apart, and bridged with rungs, a ladder is
torsionally stiff as an assembly. So too with a curved stairway when the
treads make an equivalent interconnection. Like a bumblebee, it knows what
to do.

Charles O. Greenlaw  SE   Sacramento CA