Helical Stairs

[engstructural]

Can anyone point me towards a design example for helical stairs. The stair will only have support at the btm and top (concrete). I have looked at BS5395-2 but it seems to focus on the geometry.

 

[ishvaaag]

I think the best way to do this thing today is to model the spiral slab attached to substructure enough and then apply the loadings in a 3D FEM model. Autodesk Inventor is entirely suitable for this, I think, since it can both produce the geometry and then make a linear analysis by itself. Then more than anything the stresses to be cared as for slabs.

 

[IJR]

Watch the following if you use FEM as suggested by ishvaag above:

-You will need more stiffness in lateral direction.
-The outer stringer, being longer, has more moments in vertical plane and will deflect terribly, so provide sufficient stiffness
-Model the supports correctly. A small change in modellin the supports produces terribly different results.
-if possible determine the frequency, these stairs, especially if steel, tend to vibrate
-if possible, use steps to connect the two stringers and provide torsional stiffness that way, helps to cut down deflection and lateral bending

respects
ijr