what do you think?

Here's a hint: the guardrails work like the flanges on a beam.

Hey thanks,

Well i was thinking that since it had a helical shape, it would be subjected to torsion with greater load. I was thinking that since it was a stairs it was acting as its own column self standing, but i didn't see the gaurdrails act like flanges on the beam.

still, even if it does does it deal with other stresses that i mentioned?

rebar. lots-n-lots of rebar.

it is a very stiff u-shaped channel-beam the just happens to spiral. there are probably a few eccentric loads as a result but that is not a problem if your beam depth is more than a meter...

alterantively, can be done as stacked steps, rotated...

It is an interesting question. I've never designed one of these, but the basic concept has to be that the two guard rails/stringers are essentially upturned beams, designed to handle the eccentric moments and torsion forces. The torsional stiffness could be increased by using the treads in the analysis/design, though their contribution would be minimal. I suspect those stringers have tightly packed stirrups to provide the required torsion and shear resistence, and they have reinforcing at the top and bottom for moment capacity. Additonally, because they are fairly deep beams, they likely have atleast a a few side "skin" reinforcing bars. These skin bars would also be needed resist whatever lateral moment arises. Overall it seems it would be quite involved and require a careful check of the combined stresses that result. On the otherhand, I also imagine it has been researched in the past, and most likely design resources exist.

Its really just like a reinforced concrete beam. The rebar in the concrete goes into tension (i.e. tries to stretch out) as the weight of the whole stair pushes downward. Because the spiral is continual turning at the same rate, the stress is basically equal as you continue downwards.

You have to do a fixed connection at the top and bottom to keep the spiral shape. But thats pretty easy, its just the ends of the rebar embedding in the floor at the top and bottom.

Its the same as a spring. Open up a click pen and look at the spring. Pull it apart and see how it compresses evenly when you push it together.

it an't be that hard.

mendehlson (of Einstein tower fame) did it in the 1930's in concrete at the de la warr pavilion. just as beautiful.