• Review Points

Tension structures

• It is possible to configure structural elements that have high strength and stiffness in tension, while having low or zero stiffness in compression, bending, and shear.

  • Rope
    • The fibers can slip with respect to one another so that the rope does not act as a monolithic unit in resisting buckling or bending.
    • The buckling and bending resistance of individual fibers is extremely low compared to the tension strength.

  • Chains
    • In a conventional linked chain connections between links transfer no moment or compression, shear cannot transfer across a link.
    • In a pin-connected chain, such as a bicycle chain, the connections can transfer compression, but the pin connections create a mechanism that is not stable under compression, shear, or moment.

  • Cables
    • The process of manufacturing wire makes steel stronger (though less ductile), making it possible to create elements with high tension strength but small area and moment of inertia.
    • The low moment of inertia gives low resistance to compression buckling and bending.

• Since such elements cannot resist compression, bending or shear, they do not maintain their shape (e.g. they are unstable) under changing loads.

  • This is good and bad.

  • It's good because the structure will always assume a shape so that it works purely in tension (that's all it can do), so there is an efficient use of material.

  • It's bad because it is usually impractical for a structure to undergo large changes in geometry under varying loads.

• Tension structures must always address the issue of stability, incorporating a strategy to limit changes in shape under varying loads.

  Both for small structures....

  ...and large ones.