Design Charts for Helicoidal Stair Slabs with Landing at Midspan

Helicoidal staircases are quite popular among architects for aesthetic reasons. While design charts for simple helicoidal stair slabs are available in design handbooks, no such aid is available for fixed ended helicoidal slabs with landings at midspan. This paper attempts to propose such a design tool for the practicing engineer. Because of the symmetric nature of the slab, four of the six stress resultants at midspan become zero. Thus if the two redundants at midspan can be determined, the rest of the analysis becomes a statically determinate problem. Strain energy method has been used to analyze the structure and determine these two redundants at midspan. Based on this analytical framework, charts have been proposed to quickly determine these midspan redundants. Different geometric parameters have been considered and nondimensional parameters have been used to derive the charts. Finally, the effect of a landing on the stress resultants has been investigated through a limited parametric study. It has been found that the presence of landing significantly affects the maximum vertical moment and torsion. Landing span also considerably influences the distribution of vertical moment, torsion, and vertical shear along the span.