In our report https://www.stone-ideas.com/85281/picco-engineering-floating-stone-stair/ we described the architectural reasons why post-tensioned natural stone was used for the staircase in the historical house. Here some technical details which we took from the webpage of PICCO Engineering company:
The foundation for the stairs measures 1.2 m x 1.2 m x 0.7 m (4ft x 4ft x 28″). It has to take the load of 4750 kg.
The connection at the top of the stairs is less robust. It is a steel plate bolted to an existing steel cross beam in the ceiling.
The drilled holes through the steps presented a particular challenge. They had to be extremely accurate to avoid “kinks“ in the steel cables.
The installation of the steps was carried out by Precision Stone, NY.
On a supporting scaffold, each tread was placed into/onto the other. To prevent the mortar from clogging the cable ducts, they were insulated with silicone.
Finally, the cables were tensioned by hydraulic equipment. This was the decisive moment when it would become clear whether the single steps had become a structure in one piece. Careful measurements were taken of any possible movement of the individual parts, and attention was also paid to any special noise.
A hi-flow quick curing grout poured into the cable ducts.
The supporting scaffolding was removed and the final load tests were performed.
More details are described on the webpage of PICCO Engineering.
Photos / Drawings: PICCO Engineering
(31.03.2021, USA: 03.31.2021)