thumb|right|The simplest tensegrity structure (a T3-prism). Each of three compression members (green) is symmetric with the other two, and symmetric from end to end. Each end is connected to three cables (red), which provide tension and precisely define the position of that end in the same way as the three cables in the [[Skylon (Festival of Britain)|Skylon define the bottom end of its tapered pillar.]]
Tensegrity, tensional integrity or floating compression is a structural principle based on a system of isolated components under compression inside a network of continuous tension, and arranged in such a way that the compressed members (usually bars or struts) do not touch each other while the prestressed tensioned members (usually cables or tendons) constrain the system spatially.
Tensegrity structures are found in both nature and human-made objects: in the human body, the bones are held in compression while the connective tissues are held in tension, and the same principles have been applied to furniture and architectural design and beyond.
The term was coined by Buckminster Fuller in the 1960s as a portmanteau of "tensional integrity".
Applications
Architecture
Sculptures
upright|thumb|The [[Skylon (Festival of Britain)|Skylon at the Festival of Britain, 1951]]
A conceptual building block of tensegrity is seen in the 1951 Skylon. Six cables, three at each end, hold the tower in position. The three cables connected to the bottom "define" its location. The other three cables are simply keeping it vertical.
A three-rod tensegrity structure (shown above in a spinning drawing of a T3-Prism) builds on this simpler structure: the ends of each green rod look like the top and bottom of the Skylon. As long as the angle between any two cables is smaller than 180°, the position of the rod is well defined. While three cables are the minimum required for stability, additional cables can be attached to each node for aesthetic purposes and for redundancy. For example, Kenneth Snelson's Needle Tower uses a repeated pattern built using nodes that are connected to five cables each.
Art historian Eleanor Heartney points out visual transparency as an important aesthetic quality of these structures. Korkmaz et al. has argued that lightweight tensegrity structures are suitable for adaptive architecture.
Buildings and bridges
Tensegrities saw increased application in architecture beginning in the 1960s, when Maciej Gintowt and Maciej Krasiński designed Spodek arena complex (in Katowice, Poland), as one of the first major structures to employ the principle of tensegrity. The roof uses an inclined surface held in check by a system of cables holding up its circumference. Tensegrity principles were also used in David Geiger's Seoul Olympic Gymnastics Arena (for the 1988 Summer Olympics), and the Georgia Dome (for the 1996 Summer Olympics). Tropicana Field, home of the Tampa Bay Rays major league baseball team, also has a dome roof supported by a large tensegrity structure.
thumb|left|Largest tensegrity bridge in the world, [[Kurilpa Bridge – Brisbane]]
On 4 October 2009, the Kurilpa Bridge opened across the Brisbane River in Queensland, Australia. A multiple-mast, cable-stay structure based on the principles of tensegrity, it is currently the world's largest tensegrity bridge.
Robotics
thumb|right|[[NASA Ames|NASA's Super Ball Bot is an early prototype, designed to land on another planet without an airbag, and then be mobile to explore. The tensegrity structure provides structural compliance absorbing landing impact forces and motion is applied by changing cable lengths. (Shown on Earth in 2014.)]]
Since the early 2000s, tensegrities have also attracted the interest of roboticists due to their potential to design lightweight and resilient robots. Numerous researches have investigated tensegrity rovers, bio-mimicking robots, and modular soft robots. The most famous tensegrity robot is the Super Ball Bot, a rover for space exploration using a 6-bar tensegrity structure, currently under developments at NASA Ames.
Anatomy
Biotensegrity, a term coined by Stephen Levin, is an extended theoretical application of tensegrity principles to biological structures. Biological structures such as muscles, bones, fascia, ligaments and tendons, or rigid and elastic cell membranes, are made strong by the unison of tensioned and compressed parts. The musculoskeletal system consists of a continuous network of muscles and connective tissues where the bones provide discontinuous compressive support, whilst the nervous system maintains tension in vivo through electrical stimulus. Levin claims that the human spine is also a tensegrity structure.
Biochemistry
Donald E. Ingber has developed a theory of tensegrity to describe numerous phenomena observed in molecular biology. For instance, the expressed shapes of cells, whether it be their reactions to applied pressure, interactions with substrates, etc., all can be mathematically modelled by representing the cell's cytoskeleton as a tensegrity. Furthermore, geometric patterns found throughout nature (the helix of DNA, the geodesic dome of a volvox, Buckminsterfullerene, and more) may also be understood based on applying the principles of tensegrity to the spontaneous self-assembly of compounds, proteins, and even organs. This view is supported by how the tension-compression interactions of tensegrity minimize material needed to maintain stability and achieve structural resiliency, although the comparison with inert materials within a biological framework has no widely accepted premise within physiological science. Therefore, natural selection pressures would likely favor biological systems organized in a tensegrity manner.
As Ingber explains: