The mechanical structures of bamboos in viewpoint of functionally gradient and composite materials

The structures of bamboos have been adapted to our natural environment over a long period of time. They are a composite material reinforced axially by fibers called bundle sheath. Furthermore, they have a hierarchical gradient structure, that is, a macroscopic gradient structure in culm (corresponding to trunk of wood) diameter, culm thickness and node length, and a microscopic one in the bundle sheath distribution. The macroscopic gradient structure leads to a constant surface stress at every height and the microscopic gradient structure provides a strength distribution in radial direction adapting to bending stress due to wind loads.