Simple design approach for helicoidal stair slabs

Abstract

Stair is an important functional element of a building. Presently, helicoidal stairs are gaining popularity because of their attractive appearance. However, design of the helicoidal stair is quite difficult as the exact method of its analysis is very cumbersome. Due to the complex geometric configuration of this structure, the present methods of analysis are based on various idealizations and assumptions. Under this background, finite element approach has been applied to study the validity of the current methods in use. The study has been extended further to determine the stress resultants of the helicoidal stair slab including an intermediate landing for the development of a simplified design process. The investigation has lead to a number of findings. Firstly, the existing methods of helicoidal stair slab analysis have been found to vary a little with the finite element analysis. The possibility of suggesting temperature and shrinkage steel for the design of the Ree helicoidal slab has been explored. The study resulted in a direct design approach to suggest the steel area based on geometric parameters. It is expected that the use of such direct design charts will gain popularity among the designers because of its ease of use. In addition, behaviour of helicoidal stair slabs with landing has been investigated with a view to proposing a design chart. Strain energy method has been used to analyse the structure. Behaviour of the stair with a landing could be generally outlined as the outcome of the analysis. A simple design approach has been suggested in the end. It is important to note that no design charts are currently available for the analysis of helicoidal stair slabs with landing and the charts developed as a part of the proposed design method will be immensely helpful to the designers. Also, a parametric study with a limited scope has been carried out. The study suggests that the behaviour of the stair with and without landing is similar, with the effect of landing being prominent locally, in the vicinity of the landing. The maximums of all stress resultants, excepting lateral shear, show some variations because of the introduction of an intermediate landing. The effect of landing is most prominent in torsion. The deflection of a helicodial stair with landing has been found to be larger than that without a landing.