From Left The figures on the far left are what called in mathematically the "right helicoid" vertical-section. The blades of the screw are horizontal. This helix makes the standard spiral staircase.
The 2nd figures are what called in mathematically the "oblique helicoid" vertical-section. The blades of the screw are angled.
Structurally and mathematically, "right helicoid" and "oblique helicoid" are two different things.
The 3rd figures are the vertical-section of the concrete spiral staircase.
Specifies that the top surface of the section is "right helicoid," the bottom is defined in "oblique helicoid." It has a right triangle vertical-section slab combining a right and oblique helicoids in a structure.
On the far right, each step of the stairs is written on this structure.
The bending moment of the curved slab was reduced in both the X-axis and Z-axis directions of the helix line where the force flows. I began to think intuitively that it could be made of un-reinforced concrete.
To bring out the beauty of geometry, the discovery of this triangular vertical-section, and the inspiration of the fabrication method are noteworthy.