Tensegrity, originally a portmanteau of tensional integrity, was coined by the famous Architect Buckminster Fuller, in the 1960s. It is a structural principle consisting of members, wherein isolated components exist in pure compression within a spatial network that is in continuous tension; the members in compression which are usually struts or bars, do not touch one another, whilst the cables and tendons in prestressed tension, spatially delineate the system.
The constructivist artist Kenneth Snelson named the principle floating compression. The structural system has gained quite some momentum over the past few decades, with architects, designers, and structural engineers innovating with tensegrity owing to its unique structural properties that confer enormous rigidity.
Tensegrity – in construction, biology, and beyond
Quoting Fuller here, works of tensegrity are “self-tensioning structures composed of rigid structures and cables, with forces of traction and compression, which form an integrated whole”. He was of the view that works of tensegrity were more akin to nature than those of pure compression; tensegrity is found in the biology of living creatures, like the combination of biological material like bone and muscle that enabled motion—in this case, the two only strengthened each other forming interconnected structures.
Research and development in the field of biology have revealed tensegrity to be an underlying principle behind the organization of material elements in organisms. Researcher Georgia Victor says, “It is used today to explain the organization of the elements that make up living beings according to the characteristics of their geometry. This spatial organization forms a continuous field of tensions and compressions in constant equilibrium, in a game of tensions with the force of gravity.”
The system has been extensively made use of in designing structures of varying scales, and of multiple typologies, from sculptures, pavilions, bridges, and shelters to airports and beyond.
Tensegrity in theory
The underlying concepts governing the design of tensegrity structures enable them to achieve high degrees of structural integrity and rigidity, whilst remai ning dramatically light, and thus possess a very high strength-to-weight ratio.
Their properties can be summed up as under:
- Individual members are either under pure tension or pure compression only.
- Tensional prestress and preload allow them to always be in tension, preserving the integrity of the structure.
- Members remain in compression/tension even when stress on the structure increases, because of mechanical stability.
- No bending moment is experienced by any structural member.
- Shear stresses are virtually non-existent within the system.
Such factors make the members of the system be highly optimized for the particular load carried, resulting in thin, yet efficient cross-sections.
Tensegrity Structures over time
A classic example, one of the firsts to depict the idea behind tensegrity was the Needle Tower, a public artwork by Kenneth Snelson—an abstract sculpture that tapers along its 26.5 meter height, made of stainless steel and aluminium.
The tower has a base size of 6.18m X 5.42m and has aluminum tubes held in compression, the terminal ends of which are threaded through by stainless steel cables holding the tower in prestressed tension. The steel cables appear so thin that when seen from afar, the structure seems to float mid-air without support.
A more recent precedent, of an even larger scale, is the Kurilpa Bridge (aka the Tank Street Bridge) over the Brisbane River in Queensland, Australia. Designed for pedestrians and bicyclists by Cox Rayner Architects and Arup Engineers, it is the world’s largest hybrid tensegrity bridge, wherein only the horizontal spars conform to the principles of tensegrity. It has a 128m long main span and uses 560 tonnes of structural steel that includes 6.8 kilometers of helical strand cable.
Research and Development
Tensegrity as a principle has been widely employed in multiple research projects in the domains of design and construction, to create new typologies of spaces and experiences. Plus, the aid of computational design toolkits in simulating the behavior of such systems has given an upper hand in their design and development.
A recent thesis project developed by the Designer Kuan-Ting Lai, on Reconfigurable Systems of Tensegrity at the University of Stuttgart explores the application of tensegrity in creating transformable architectural spaces. Consisting of only two kinds of structural components—parallel struts of pneumatic cylinders and polycarbonate panels, the project explores multiple configurations that could be achieved based on the principles of tensegrity, responding to the lighting and ventilation conditions in the surroundings.
The responsiveness in the design is achieved by varying the lengths of the struts, which in turn had a greater effect on controlling the global geometry of the structure. The evolution of the project was simulated using Kangaroo 2 in the Grasshopper environment to understand how the system behaved owing to changing strut lengths.
From the architecture of cellular organelles to the design and construction of reconfigurable spaces, the applications of Tensegrity as a principle, know little bounds and for a large part remain scarcely explored within the AEC industry, with multiple trajectories forward.
References:
- Matheus Pereira – Tensegrity Structures: What They Are and What They Can Be – Archdaily
- Fabian Dejtiar – This Adjustable Tensegrity Structure is Constructed From Just Two Structural Elements – Archdaily
- Samantha Pires – 8 Incredible Structures Around the World That Use Tensegrity to Defy Gravity – mymodernmet.com
- Wikipedia – Tensegrity
- Wikipedia – Needle Tower
- Wikipedia – Kurilpa Bridge
