120 Cables

A grand helical staircase created by Agence Nicolas Michelin & Associes for the National Libary in Strassbourg coiling around 8.10 m radius was built in segments. Once landings were attached to the concrete floors, the flights of stairs were soldered by sections on the spot, before being hoisted up to 12 meters. The whole staircase was then hung at 27.5 meters from the square base of the dome’s spire by 120 brushed steel cables. Its shape was obtained by installing a circular ring at the confluence point of two conical revolutions.