National Gallery Millenium wing (floating stairs)

hi!

Does anyone know the construction details for the ‘floating’ stairs in the entrance hall of the National Gallery. The treads on the stairs seem to be made of terrazzo or some kind of precast concrete and appear to float- but are held in place by hidden metal bolts. The floating stairs contribute to the wonderful sense of space in the entrance hall- I am studying various stairs for a project at college.

I would like to know the technical term for this type of stair construction and if possible where I could find more information about them (books or web).

many thanks,