Abstract
Wild bamboo is a plant which has many peculiar stiff nodes and tissue structures. It has a hollow cylindrical shape, which gives it strength over its height, although there is a risk of losing resistance to bending. The purpose of this study is to examine how the nodes and vascular bundles contribute to bamboo's bending resistance by forming a nearly optimal shape, obtained over millions of years of evolution. From a standpoint of structural mechanics, bamboos can be modelled as cylindrical shells with ring stiffeners. In addition, cylindrical bamboos are regarded as a functionally graded structure due to its distribution of vascular bandles in the cross section of cylinders. From the measurement data analysis and theoretical formulations, we found that wild bamboos effectively control their node spacings as well as other geometric parameters corresponding to the bending moment diagram along the vertical direction. Moreover, we demonstrate theoretically that the vascular bandle distribution enhances the flexural rigidity of bamboos. These new findings give us the possibility of a new design concept of lightweight and high-strength functionally graded structures.
