竹の節・組織構造が織り成す円筒体としての合理的な構造特性の理論的解明  [in Japanese] OPTIMAL STRUCTURAL PROPERTIES OF CYLINDRICAL STRUCTURES LEARNING FROM MORPHOLOGY OF WILD BAMBOOS WITH PECULIAR NODES AND VASCULAR BUNDLES  [in Japanese]

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Abstract

自然界に生息するタケは中空円筒であり,かつ節と組織構造を有する植物である.これは適者生存の厳しい環境下でできるだけ強く,高く生育するためにタケ自身が進化の過程で獲得してきた形態であり,力学的に極めて高い合理性を有すると考えられる.本研究は,タケの生態を構造力学的に紐解き,節配置の高さ方向分布と維管束の横断面内分布の不均一性が織り成す力学的優位性を実証するものである.この研究により,曲げを受けるタケの節配置による断面偏平抑制効果を剛性に関する異方性を考慮した無次元パラメータにより記述し,タケが外力により生じる曲げモーメント分布に合わせて断面偏平を効率的に抑制していること,また横断面内維管束分布は曲げ剛性を高めるように効果的に配置されていることが初めて理論的に示された.

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.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM))

    Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)) 72(2), I_25-I_34, 2016

    Japan Society of Civil Engineers

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