The client wanted a stone staircase but without the traditional detailing. Working with the stonemason Ian Knapper we developed a tread with a scalloped soffit, which resulted in a triangular cross section at the wall end of the tread and a sawtooth stringer cross section at the balustrade end.
As the proposed tread cross section at the balustrade end was substantially weaker in torsion than the traditional triangular cross section, we carried out detailed analysis of this tread shape to confirm the minimum strength of the stone that would be required. We also carried out load tests on full size treads with the proposed cross section to confirm the design.
The solid stone half-landing slabs taper from 155mm thick at the wall to only 75mm at the balustrade end. With the stone being so thin where the metal balusters were pocketed into the top of the slabs, we also carried out testing of the balustrade connection to prove that the stone was strong enough.