  Hollow-section columns are one of the mechanically superior structures with
high buckling resistance and high bending stiffness. The mechanical properties
of the column are strongly influenced by the cross-sectional shape. Therefore,
when evaluating the stability of a column against external forces, it is
necessary to accurately reproduce the cross-sectional shape. In this study, we
propose a mathematical method to describe a polygonal section with rounded
edges and vertices. This mathematical model would be quite useful for analyzing
the mechanical properties of plants and designing plant-mimicking functional
structures, since the cross-sections of the actual plant culms and stems often
show rounded polygons.
