Bamboo (Phyllostachys spp.) culms exhibit hollow and tapered geometries with remarkable mechanical robustness, yet the mechanical significance of these morphologies remains poorly understood. This study aimed to understand the biophysical parameters of bamboo stems and explore why they are tapered and hollow, while taking different loading conditions into consideration. Representing stems as hollow, tapered beams, tapering ratios were assessed for their ability to minimise maximum bending stress. An ‘optimal tapering law’ was derived for an axially graded, hollow, tapered cantilever beam under uniformly distributed load and compared to a beam under point load. Theoretical analysis was conducted to investigate how loading and hollowing of a beam made from axially functionally graded material affect the optimal tapering ratio. This law helps explain bamboo’s hollow, tapered structure, demonstrating that stems follow optimal tapering laws suited to their growth environments. These can be translated into general design rules for lightweight, wind-resistant structures.
