This unique circular staircase at my casa in Mexico has no center support. It's 24 steps allow a 12' rise in a 10' diameter circular stairwell. I designed an built it with help from my son.
Circular stairs usually need a center support, but I wanted to have the center open, so I designed this one to cantilever from the wall, leaving a 3' open center.
To accurately form the wall and steps, I cut a dozen 5' -1/6's from 3/4"
Rotating same boards around the pipe gave us the riser forms to pour the actual steps onto the ramp.
Step 1: sketchup plan
Drawing it in sketch up made it possible to calculate step rise and run, rebar placement, and step placement.