All you need to know about tensile structures
When I was doing my second year in architecture I stumble upon tensile structure and my life changed from then on.
At that time the Olympics at Munich was on, and I remember distinctively when I saw the stadium on TV that whatever happened I would be an architect. The Munich Olympic Games was a powerful example of what could be done with these structures. The 1972 Olympics was hosted in Munich and subsequently in 1974 the World Cup. The creator of the stadium, (pictured here) with its characteristic textile cover of PMMA, was the architect Frei Otto.
This type of structure was my secret love, kept clandestinely in my mind and waiting to be presented to the world at any time in a future project. The gods had other ideas about my profession, time has past and unfortunately I have not been granted a project where I could introduce a tensile structure as part of the solution. Nonetheless, although I haven’t had the chance to use it, I thought that maybe I would share with you readers the techniques, so thus this article.
Historically inspired by tents, one of the first shelters conceived by man, tensile structures offer a series of benefits when compared with other structural models. Tensile structure is the term usually used to denominate the structures that mix membranes and steel cables to build large roofs, whose main characteristics are tensile strength, prefabrication, and formal malleability. This type of structure requires very little material, thanks to the use of thin canvas that, when stretched, create surfaces capable of overcoming the forces imposed on them.
Predominantly used to cover sports centres, stadiums and industrial and agro-industrial constructions, the tense structures are inspired by ancient systems, used during the Roman Empire. However, from Roman times until the middle of the 20th century, due to low demand and the lack of cable, canvas and connection manufacturers able to withstand the forces generated, there were few technological advances. It was only after the Industrial Revolution, and the unleashing of the Ford era, that the new developments were able to satisfy the intrinsic needs of this construction system. The low cost of mass production and the demand for systems capable of adapting to the most varied terrains through large openings, such as circus tents, for example, encouraged the development of the technique.
Steel cables and waterproof membranes
The instability and structural deficiencies of some previous models, due to the application of interwoven cables and very light covers, was resolved in the middle of the last century, thanks to the application of steel cables and waterproof fibre membranes, with a high degree of resistance. These not only provide greater protection against ultraviolet rays, fungi and fire, but also allow a greater or lesser translucency and reflectivity.
Such progress was only possible thanks to the physical-structural studies initiated by the German architect and engineer Frei Otto, who from the 1950s made the first scientific studies and designed the first covers with tensioned steel cables, combined with membranes.
As a student, Otto visited Fred Severud’s office, getting to know the Raleigh Arena in North Carolina and being impressed by the bold aesthetics and comfort of the project. Back in Germany he began to explore physical models on a small scale, empirically generating several surfaces, using chains, pulled cables and elastic membranes. Very much the method used by Antonio Gaudi in Barcelona.
The idea is to use chains to cover a space, invert those chains (upside down) and gravity provides you with the ideal and most economical form for the arches to span from.
More simply, if you take both ends of a chain with your hands and let the chain form an arch and if you could freeze that arch, and then keep adding more chains to cover a space that would be the most economical membrane to cover a space.
Frei Otto, the master architect
Convinced of the usefulness of stretch ceilings, he developed the first large scale project using the system that would later allow them to cover the Olympic stadiums, clubs, zoos and pavilions. In 1957, he founded the Centre for the Development of Light Construction in Berlin. Seven years later, in 1964, he created the Institute of Light Structures (The Institut fur Leichte Flachentragwerke) at the University of Stuttgart, Germany.
Author of notable projects, such as the German Pavilion for the 1967 Expo in Montreal and the Olympic Stadium in Munich in 1972, Frei Otto is famous for his intense research work, for which he was honoured with the RIBA Gold Medal in 2006 and the Pritzker Prize in 2015.
Otto is also the author of the first complete book on tensile structures, Das Hangende Dach (1958), intensifying the idea of reinventing material rationality, prefabrication, flexibility and luminosity in the interior space, and even sustainability, when the term was not yet used in architecture.