Knut Göppert
Right Spoked wheel principle
The Spoked Wheel for Ring Cable Roofs in Lightweight Construction
The spoked wheel, which everyone is familiar with from the bicycle, is an extremely material- conserving and clever structure. In the bicycle, tension members known as the spokes transfer the loads between the ground and the axle. To ensure the necessary lateral stability, the spokes are spread apart slightly toward the hub, which allows loads perpendicular to the plane of the wheel to be redistributed as well. These are the properties that are put to use by orienting a wheel horizontally, so that wind and snow loads are transferred out through the flared spokes. But how is it possible for such a delicate structure to withstand such high loads? The answer to the riddle is pretensioning: the many spokes of the wheel are pretensioned between the compression ring (the rim) and the hub. Though exterior loads will change the forces within the spokes, the spokes will always remain under tension. They stabilise the rim, so the support structure can remain slender even though it is under compression. A system tensioned in this way, in which the hub can be replaced as needed with a tension ring, can be used for many building tasks and is especially suited for large-span roof structures. Using a few tricks and keeping in mind the appropriate equilibrium conditions, it is even possible to evolve the form from the circular bike wheel to a curved rectangle. Roofs like this are known as ring cable roofs. There are four main reasons that favour the ring cable roof principle: Economy – All interior forces are s hort-circuited. This represents an elegant solution to a p roblem that commonly arises in lightweight construction: the large cost of the foundations. The building components are defined as purely tensile or compressed structural elements, v irtually free of bending moments, so that they can be
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Horizontal spoked wheel
The spreading of the spokes radially outward; two compression rings, one central point
Expansion of the central point to a circular tension ring
The Spoked Wheel for Ring Cable Roofs in Lightweight Construction