We have a 3-story historic stair with curved sections that is leaning inward on itself. This stair is self-supporting - there is only direct structural support under the first floor section, everything else, including the platforms, is floating. There are no columns either. We have exposed the structure, shored up the base and begun jacking it back to level and reinforcing and basic shoring up, but the stair continues to fall back out of level.

Instead of wasting more time guessing at this, is anyone familiar with this sort of problem that knows how to fix it? Do you know of any links to information that may be helpful?