FREI OTTO AND THE TENSILE STRUCTURES

To write a paper about tensile structures it is in fact to write about Frei Otto. And this text will reserve him a central role. Even though it is also possible to start a tale on these fascinating structures long before that the brilliant German architect had been involved with them.
Tensile structures can be defined as load-bearing structures in which most of the elements are not capable of compression and flexural strength. In other words, most of the elements do not have a definite shape of their own but assume what the tension stresses assign to them in mutual contrast with the other elements. This is why tensile structures could be defined as structures deriving from “active tension” in the same manner that timber post form gridshells (of which Otto himself was a sublime interpreter) can be defined as structures deriving from “active bending”.
Thus all the tents belonging to the ancient nomadic and military building traditions as all the “velarium” used to shade and protect parts of ordinary constructions (see for example the coverings of Roman amphitheatres) or even the Tibetan bridges and, at least in part, all types of suspension bridges can all be classified as tensile structures. Actually the modern tensile structures arouse when the three-dimensional complexity of ancient “velariums” and traditional tents shapehad met the almost completely two-dimensional geometric-structural rigor of suspension bridges. […]