Tensairity

Comparison of Tensairity girder (b) and normal steel framework girder (a). When load is aplied in top-down direction trying to bend girder force is acting on uper rod of any girder as comperssiona stress, and on lower part as tension. This stress tends to decrease girder width making it less rigid (Girder of zero width has zero flexural strength). In order to prevent this uper and lower rod has to be kept apart. In classical framework girder this is ensured by triangular framework. In tensairity girder gas pressure in air bag is used instead. Lower rod loaded in pure tension can be replaced by rope or the airbag membrane itselfs. This leads to much better strength-to-weight ratio

Tensairity is a registered mark. Circle R. Tensairity is a foundational structure using inflated airbeams and attached stiffeners or cables that gains mechanical advantages for low mass. Pneumatic structures using tensairty are solving problems. The structure modality has been particularly developed by Mauro Pedretti.

Known applications

Bridge, band stand , aircraft wing construction

Related technology

A related structure modality is tensegrity. Conceivably, an ultralightweight structure evacuated of air would float in the atmosphere, much as a buoy floats in water A crushing load is present destabilizing such structures. However, enclosed-air structures perhaps made of tensairity beams in a tensegrity format holding an enveloping skin could be heated by solar energy and interior activity and then become lighter than air, like hot-air balloons. A torus of 72 inch major diameter and 27 inch minor diameter displaces about 5 pounds of atmosphere, so if the torus weighed less than 5 pounds, and was evacuated, it would be buoyant. Buckmister Fuller designed floating cities (air-filled) so lightweight that they would be buoyant only by the effect of solar heat warming the air within to slightly less density than the surrounding air. As domes, they were about 1/2 mile diameter. As floating spheres the cities would not experience earthquakes.