Design Engineering

Bamboo provides optimal design for lightness and rigidity


Materials bamboo

Researchers found that the spatial distribution of fibers in hollow bamboo cylinders is optimized to reinforce flexural rigidity.

Bamboo is being used for more and more applications including room flooring to Ford including it in their vehicle components. A group of researchers is exploring new approaches to developing this material.

Researchers from Hokkaido University, Prefectural University of Kumamoto and the University of Yamanashi found that the spatial distribution of fibers in hollow bamboo cylinders is optimized to reinforce flexural rigidity.

Bamboo is light due to its hollow structure, but this lightness is somewhat of a challenge for the plant as it can be difficult for it to support its own weight. Bamboo has naturally overcomes this through thin, robust fibers (vascular bundles) that reinforce the structure. Each fiber is as rigid as steel.

bamboo structure material

Fibers (vascular bundles) surrounding the heart-shaped black openings have a denser distribution toward the outer part. Photo credit: Sato M., et al., PLOS ONE, May 3, 2017.

However, the fibers in the wood are not evenly distributed — the density of the fibers becomes gradually thicker from the inner to the outer surface. Mechanically speaking, this means the outer parts are stronger than the inner parts. This is reasonable because the outer parts receive more force when the cylinder is bent.


To determine the relationship between the distribution of the reinforcing fibers in a culm and the culm’s flexural rigidity, the team compared the data from the real bamboo’s fiber distribution to the theoretically derived optimal fiber distribution.

Real bamboo data displayed almost the same fiber distribution as the one with the theoretical, optimal fiber distribution. Near the root of the culm, where a large number of fibers are found, the real fiber distribution matched the theoretically derived quadratic form for gradient distribution. Near the tip of the culm, where there are much fewer fibers than near the root, the experimental data matched the linear distribution calculated in accordance with the theory.

Bamboo naturally adjusts the distribution of fibers so flexural rigidity is maximized with the smallest volume of wood material possible, the team discovered. The mechanical theory employed in this research, therefore, can be applied to other hollow cylinders to determine the gradient distribution that can optimize flexural rigidity.

“Our study could help develop advanced materials by mimicking the bamboo model for its lightness and toughness. Imitating the systems of animals and plants which have survived harsh conditions, an approach called biomimetics has proved successful in solving many problems in the development of materials in recent years,” commented Motohiro Sato, the lead author at Hokkaido University.


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