We are all familiar with bamboo, which is thin and long. It is rare to see bamboo being blown off in a typhoon. A typical section of bamboo includes bamboo nodes and internodes, in which the internodes are hollow, and all materials are concentrated on the outside, which reduces the self-weight and increases the moment of inertia of the entire section at the same time, and its microscopic characteristics also reflect the same law, the closer to the edge, the denser the cells are, which maximizes the moment of inertia of the entire section.
There is a diaphragm inside the node, which prevents the local instability and damage of the column due to the excessive length. Bamboo joints are not evenly distributed, and the distribution is denser at the bottom and top, while the distribution is sparser in the middle section. At the same time, the diameter of the bamboo joints is gradually reduced from bottom to top, which also reduces the wind load virtually.
These properties of bamboo were used in the structural design of the China World Trade Center. The tower is divided into eight sections in the height direction, and the bottom bears the greatest force, so the length of the bottom internodes is small to enhance the stability of the tower. At the same time, the diameter of the structure gradually decreases from bottom to top to reduce the effect of wind load. And imitating the shape and characteristics of bamboo, the shape and wall thickness are mathematically expressed.
