# Tensegrity

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Tensegrity or tensional integrity is a type of structure with an integrity based on a balance between tension and compression components. In a tensegrity structure the compressive members are connected to each other by tensile members.

The term tensegrity was coined by Buckminster Fuller.

## Contents

### Concept

Tensegrity structures are structures based on the combination of a few simple but subtle and deep design patterns:

• loading members only in pure compression or pure tension, meaning the structure will only fail if the cables yield or the rods buckle
• preload or tensional prestress, which allows cables to be rigid in tension
• mechanical stability, which allows the members to remain in tension/compression as stress on the structure increases

Because of these patterns, no structural member experiences a bending moment. This can produce exceptionally rigid structures for their mass and for the cross section of the components.

A conceptual building block of tensegrity is seen in the 1951 Skylon tower. The long tower is held in place at one end by only three cables. At the bottom end, exactly three cables are needed to fully determine the position of the bottom end of the spire so long as the spire is loaded in compression. Two cables would be unstable, like a person on a slackrope; one cable is just the limit case of two cables when the two cables are anchored in the same place.

A simple three-rod tensegrity structure (shown) builds on this: locally, each end of each rod looks like the bottom of the Skylon tower. As long as the angle between any two cables is smaller than 180° as seen looking along the rod, the position of the rod is well defined. What may not be immediately obvious is that because this is true for all six rod ends, the structure as a whole is stable. Variations such as Needle Tower involve more than three cables meeting at the end of a rod, but these can be thought of as three cables defining the position of that rod end with the additional cables simply attached to that well-defined point in space.

Eleanor Hartley points out visual transparency as an important aesthetic quality of these structures.[1]