This is a simple spiral staircase -- with chequered plate treads welded to tees, which in turn are welded to a circular hollow section post. Balusters and railing are of circular hollow sections, too. I supposed the post should be mounted on a base plate that is bolted to a solid base.
The principle modelling process took less then 30 minutes to complete. The model of this staircase can be found in 3D Warehouse, as below.
Updates: I made an animation with this model, on this page.