Abstract:
Attractive appearance of the helicoidal stair slab has drawn the attention of the
users and architects. For this reason, the structure is now being increasingly used
in many buildings. Due to complex geometric configuration of this structure, the
conventional methods of analysis are based on different idealisations and
assumptions. All these analytical methods fail to utilise its inherent structural
efficiency that is derived from the helicoidal shape. With a view to developing a
rational design procedure for this structure, finite element approach was introduced
to study the actual behaviour of heliocidal stair slabs without any geometric
idealisation using eight node curved thick shell element.
The results of finite element analysis were compared with those obtained from the
traditional helical girder solution. The comparative investigation revealed that the
helical girder solution largely over estimates the vertical moment, lateral moment,
lateral shear force and thrust with an under estimation of torsion. Apart from these
aspects, the sensitive non-linear response of the structure due to the variation of
different geometric parameters including central angle was also distinctly observed
from an extensive parametric study.
The investigation on the effect of variation of mesh size on the vertical
displacement for an 800 stair indicated that a coarse mesh (even 2 x 4) is also
capable of performing the analysis satisfactorily. Evidently this confirms the
efficiency of the developed software and displays the power of the "Curved Shell
Elements". The deflection pattern and the load deflection response of the structure
were also found to be in good agreement with the available results of model
studies.
Based on all these findings, a rational design procedure based on finite element
analysis has been proposed. A comparative design exercise has illustrated that
around 37% overall economy of reinforcement is attainable in the proposed design
process.
