The common kitchen sieve served as the inspiration for the innovative method of constructing grid shells – by fashioning the mesh into a rhomboid shape, a net with quadrangular mesh can be formed so as to adapt to any surface gemetry. When combined with a diagonal cable net, the net becomes an ideal membrane shell, and when covered with glass panes becomes a light and transparent roof. This is an alternative to a triangular mesh surface structure. In both cases the load-bearing and glass layers are merged with one another, as the glass planes lie directly on the net´s slats, making the usual secondary structure unnecessary.
Slender, filigree footbridges nestle into the landscape or are moulded out of it. Their aesthetic quality can best be understood and experienced while walking across them. They vibrate slightly under a load or begin to move dramatically in order to open or close. They are delicate in detail, while while remaining appropriate to human scale, and are both robust and easy to maintain. They also convey the full pleasure of design: Designing a pedestrian bridge is always more than merely rendering a service and every poorly-designed ‘eyesore’ is a missed opportunity.
Cable nets are both space-forming and load-bearing structures, whose diverse forms are not primarily the result of pure creative will, but rather the product of strict physical principles.
A bicycle’s spoked wheel consists of a thin rim, spokes, and a central hub. By itself, the rim would turn into an oval if subjected to the slightest of loads, but due to the addition of thin spokes it becomes surprisingly stiff both along its plane as well as transverse to it. Spokes are prestressed in order to keep them under tension, and this allows for the transfer of the load between the rim and the hub through the sole use of highly efficient tensile members. The positive side effect of this is that the rim becomes a compression ring, which leads to an overall increase in stability.
A looped cable roof is the transformation of the spoked wheel, which is primarily loaded along its plane into a structure with vertical load dispersal. It combines the characteristics of both cable and membrane structures: A wide-meshed, primary load-bearing structure of cables stretches between the roof’s closed, self-anchoring tension and compression rings, while a prestressed membrane, the secondary load-bearing structure, is stretched between the cables.
A vertical cable net with quadrangular meshes, stretched in a frame like a tennis racket, can bear horizontal wind loads of almost any magnitude. The higher the prestressing of the net is, the smaller the deformation and the greater the cable forces are. This structural type is ideally suited to the creation of seamlessly transparent glass façades.
Textile membrane roofs span great distances, are light-weight and translucent, vibrant and adaptable, and are even used as retractable roofs. They combine load-bearing and protective functions in one. Masts and guying cables define the high and low points, thus producing the required surface curvature. Because of the interdependence of external shape and inner forces, membrane structures cannot be designed at will. Instead, their form is the result of a search for, and determination of, an equilibrium. . Instead, their form is the result of a search for, and determination of, an equilibrium.
Nothing could be lighter—the allure of air-inflated roofs, which are airy and light, and yet protective, lies in the elegant appearance of air-inflated cushions and their economic use due to a low overall weight. This last aspect also means they are easy to dismantle and re-erect, and can be used on a seasonal basis or according to weather conditions.
A girder that is curved in plan view—a circular ring girder—only needs to have a hinged support along a single line to keep it from flipping downward. If it has bearings on the inside edge, the line load causes ring tension on the upper side and ring compression on the lower side of the slab, whereas it is the other way round for a line support on the outer edge. The efficient form of a curved arch in plan view is manifested in the principle of inversion: The arch is shaped the same as a hanging cable.
Sweeping, rounded forms, similar to the rounded shape of a fork in a tree’s branches, are characteristic of cast steel components. The flowing forms avoid damaging concentrations of stress and notch effects. Cast steel enables the production of complex, individual, steel tube joints and allows for an optimal adjustment to the flow of forces.