Saturday, April 4, 2009

Membranes. Tensioned structures

Membranes and other similar products (suspended structures, hanging roofs, membrane roofs, tensile structures, etc.) were initiated by some eminent structural designers, architects and builders: Frei Otto, Horst Berger, Ted Happold and others (Otto,1954, Drew, 1979, Schock, 1997, Robbin, 1996). Following some smaller and experimental suspended roofs, the Olympic Stadium in Munich in 1972 was the first major realization of a long-span hanging roof. This had a roof assembled from acrylic panels, which, however, was an inappropriate material in view of the required lifespan of roofs.

The next step was the introduction by the American Horst Berger of Teflon-coated fibreglass. This opened the way to a broad application of membrane roofs. The first such structural membrane roof was built in 1973 at the University of La Verne, California, USA. The most important membrane roof hitherto has been the Haj Terminal at the King Abdullah International Airport, Saudi Arabia, 1981. Its Teflon-coated fibreglass membranes were designed by Horst Berger in cooperation with David Geiger and Fazlur Khan of Skidmore, Owings and Merrill. This roof covers 460 000 square metres and is up to now the largest roof structure in the world. It comprises 210 tents, each of them with a surface of over 2000 square metres. As could be expected, it required the elaboration and realization of complex structural design, fabrication and assembly plans.

Haj Terminal, Jeddah, Saudi Arabia, 1981, structural designer: Fazlur Khan.
Tent roof system, 460 000 square metres in area.

Besides tents, tensioned roofs often follow in some way the form of umbrellas (Rasch, 1995). An equally important building covered by Tefloncoated fibreglass membranes was constructed at the Denver International Airport. The major designers were Horst Berger, Severud Associates and James Bradburn (Robbin, 1996). The roof is extremely light at 2 pounds per square foot. This is vividly illustrated by noting that if it were built from steel, its weight would be 50 times more and if from steel and concrete, yet more. In spite of its lightness, it bears the large snow loads of the region and it permits the passage of daylight sufficient for the requirements of the space below the roof. The roof consists of a series of tent-like modules supported by two rows of masts with a total length of 305 metres (Berger and Depaola, 1994). Along with the American firm Birdair, the Japanese Taiyo Kogyo Corporation may lay claim to being one of the world’s leading fabricators and installers of architectural membranes.

In the major components of tensile or tensioned structures, tension stress only is present. The important components are the masts (pylons, etc.), the suspending cables or other supports (arches, trusses), suspended roofing: metal sheet, foil, or fabrics and specially designed and constructed edges (clamped edges, corner plates, rings and others). Two basic surface forms are mostly used, individually or in combination: the synclastic and the anticlastic shapes. Spheres and domes are examples of synclastic surfaces. Saddles (hyperbolic paraboloids, i.e. hypars) are common for anticlastic shapes.

A special class are the tensegrity (tensional integrity) domes (Buckminster Fuller, 1983, Kawaguchi et al., 1999). Tensegrity structures have a geometry in which there are relatively few compression members and a net of pure tension members. The compression members do not touch, making a ‘tensegrity’. Richard Buckminster Fuller (1895–1983), an American inventor, was the first to develop the tensegrity structures. His invention (and patent) was also the geodesic dome in which the bars on the surface of a sphere are geodesics, i.e. great circles of the sphere. Fuller based his domes on the geometry of one of the regular polyhedra (tetrahedron, cube, octahedron, dodecahedron, icosahedron). Other designs were using semi-regular poyhedra that comprise more than one type of regular polygon and other forms. One of the first geodesic domes was built at the Ford plant in Detroit in 1953 with a 28-metre diameter in which bars were connected to form triangles and octahedrons were built up from these. Following this, a great number of such domes were built all around the world, among them the ‘Climatron’ Botanical Garden, St Louis, Missouri (1960), and the one assembled in Montreal, Canada, 1967, with a height of 50 metres. Many variants of the geodesic dome have been developed during the years since its inception.

Sebestyen, Gyula. 2003. New Architecture and Technology.

1 komentar:

Hels April 2, 2009 at 7:02 AM  

I have picked up the two of your posts that I enjoyed most and have opened up a dialogue in my blog. If you would like to discuss my questions further, that would be fantastic.

Art and Architecture, mainly

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