Tensegrity

Tensegrity is a structural principle that combines compression elements with tension elements to produce a stable, rigid form. The name tensegrity was coined in the mid-twentieth century and is a combination of the words tension and integrity. It has also been referred to as floating compression because the solid compression elements seem to be “floating” in a web of tension elements, such as wires or cables. The basic concept of tensegrity comes from the interconnection of elements found in weaving. The principle has been used in architecture to create sculptures, bridges, and sports stadiums. It is also one of the founding principles of the structure of the human body and other living creatures.

Background

All human-made and biological structures must deal with forces placed upon them by Earth’s gravity. These forces take the form of stress that manifests itself in two ways: compression and tension. Compression is the force that squeezes or pushes material inward. Tension is the force that tries to pull material apart. Structures under too much compression stress can collapse or buckle. Structures under too much tension stress can snap or break. For a structure to maintain its stability, it must find a way to dissipate, or spread out, these forces.

The curved architectural structure known as an arch is well suited to handle compression stress. An arch dissipates compression force by channeling it through its support columns and into the ground. Solid objects are better able to handle compression stress, but they are not equipped to handle large amounts of tension stress. When ropes or cables are pulled taut, they are capable of spreading out tension stress over their length. Tension forces increase when a rope is pulled, making the rope stiffer and stronger. At the same time, ropes cannot handle compression forces well and bend or collapse when pushed.

For most of human history, structures were built using compression materials that dissipate stress through structural supports. For example, the solid materials used to build houses compressed against each other and kept the structure intact. Roofs and ceilings spread the force into the walls; the walls spread it into the foundation, and the foundation spreads it into the ground. Tension elements were used occasionally, especially in the construction of bridges. Longer bridges need more supports to dissipate the compression forces. One way around that is to use suspension cables to transfer some of that force into tension stress.

Overview

In the late 1940s, college student and artist Kenneth Snelson began experimenting with architectural designs using solid bars arranged in an x-shape held together by tensioned strings. One of his professors was architect R. Buckminster Fuller, who incorporated Snelson’s concept into his own work. In 1961, Fuller coined the term tensegrity to describe a structure that incorporates freestanding compression elements inside a network of continuous tension elements. Fuller was best known for designing geodesic domes, which are round, lattice-work structures that use some of the principles of tensegrity. Although Fuller did not design it, one of the most famous examples of a geodesic dome is Spaceship Earth at Walt Disney World’s Epcot theme park in Florida.

Tensegrity structures are a system of solid compression elements that are held together by the tension stress generated by connected strings, wires, or cables that act as a framework. The solid elements do not touch each other but are used as “spacers” to add shape to the structure and maintain the proper amount of tension. The solid elements appear to be suspended, or float, in a web of wires. The majority of the stress of a tensegrity structure is dissipated into the ground through the tension elements.

In order for the structure to maintain its stability, the tension elements must be pulled taut. During construction, a tensegrity structure must be built in one piece. The solid pieces can then be rotated or moved, changing the structure’s shape until they are in the proper position to create enough tension stress to hold the structure together. If an additional weight is added to any point in the structure, the whole structure can adjust itself to handle the extra stress. However, if too much stress is placed on an element, causing one piece to fail, the entire structure will collapse. The same result will occur if one element is removed from the structure.

In architecture, tensegrity structures are known for their aesthetic qualities that bring to mind the art of weaving. They are also flexible and can easily be collapsed, folded, and moved if the need arises. One of the most well-known tensegrity sculptures is Needle Tower, a work of art created by Kenneth Snelson in 1968 at the Hirshhorn Museum in Washington, DC. The concept of tensegrity has been used to build the former Georgia Dome, a stadium in Atlanta, Georgia, that was home to the National Football League’s Falcons from 1992 to 2016. In Argentina, the design was used in the construction of La Plata Stadium in Buenos Aires. Kurilpa Bridge, a pedestrian and cycling bridge in Brisbane, Australia, is another structure built using tensegrity design.

The principles of tensegrity can also be applied to the physical structures of some biological organisms. In human beings and other creatures with an internal skeleton, most of the skeletal bones are not attached directly to one another but are held together by connective tissues such as ligaments and cartilage. The solid bones of the skeleton are further held in place by the muscles and skin that surround them. In this analogy, the bones act as compression spacers while the ligaments, muscles, and skin act as tension elements that keep the physical structure intact.

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