Space Structures

The development of space trusses led to the creation and application of truss systems with specific types of node: MERO, Unistrut, Triodetic, Moduspan, Harley Mai Sky, Catrus, Pyramitec, Nodus and others. The MERO system in fact was one of the first space grid systems and it was introduced in the 1940s in Germany by Dr Max Mengeringhausen. To this day it remains one of the most popular in use. It consists of prefabricated steel tubes, which are screwed into forged steel connectors, the so-called MERO ball. Up to 18 members can be joined with this system without any eccentricity.

The two basic types of these systems are the flat skeletal grid and the curvilinear forms of barrel vaults and braced domes. In the flat skeletal double-layer grids two parallel lane grids are interconnected by inclined web members. The grids may be laid directly over one another (direct grid) or be offset from one another (offset grid). These basic relations lead to different geometries of the system. Lamella domes and vaults consist of interconnecting steel or aluminium units. An important innovative step was the invention by Buckminster Fuller of the geodesic domes, to which reference has been made earlier.

The space grid systems mostly use circular or tubular members and their nodes may be characterized as solid or hollow spherical nodes, cylindrical, prismatic, plates, or nodeless. Most of these systems are double layered in that a top and a bottom layer composed from linear bars are interconnected by vertical or inclined, equally linear, members. The bars of single-layer space grids are usually positioned on a curved surface. A recently proposed new type of space grid is the ‘nexorade’, which is assembled from ‘nexors’. Nexors have four bars (eventually scaffolding tubes) and these are connected at four connection points, two at the ends and two at intermediate points by swivel couplers (Baverel et al., 2000). The various space grids provide abundant inspiration for creating different structures including domes, vaults and irregular structures and, thereby, have an important role in architectural design.Domes and vaults assembled from space trusses have taken on a great variety. One of the world’s largest is the hypar-tensegrity Georgia Dome (structural designer: Mathys Levy in cooperation with his co-workers at Weidlinger Associates, 1992). It has a sophisticated structural scheme. Its ridge cables make rhombs and its cables lie in two planes.

Georgia Dome, Atlanta, Georgia, USA, 1992, structural design: Mathys P. Levy, Weidlinger Associates.
Widespan roof, the longest span hypar-tensegrity structure made.

Deployable structures make temporary scaffolding unnecessary. Mamoru Kawaguchi designed the Pantadome system employing a series of hinges so that the completed dome can be raised all at once (Robbin, 1996). Kawaguchi’s first Pantadome was built in Kobe in 1985. He also designed the Barcelona Pantadome in cooperation with architect Arata Isozaki, which was at first preassembled and then raised with jacks and temporary support towers. Tensile structures may be two dimensional (suspension bridges, cable-stayed beams or trusses, cable trusses), three dimensional (cable domes, truss systems), or membranes (pneumatically stressed surfaces, prestressed surfaces).

Palau Sant Jordi, Pantadome, Barcelona, Spain, design: Mamoru Kawaguchi and Arata Isozaki.The space frame was built in the arena floor bowl, then raised with jacks and temporary support towers; in total 12 000 parts, specified with only 40 Formex expressions.

Structural design must deal with specific risks related to thin, tensile structures: non-linearity, wind uplift, buckling, stiffness, horizontal instability, temperature conditions, boundary conditions, erection methods.

Sebestyen, Gyula. 2003. New Architecture and Technology.

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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.

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Wide-Span Structures

Spaces with a large surface with or without internal columns (supports) and bridges with long spans have been constructed since ancient times. Domes, up to the nineteenth century, had a maximum span of 50 metres and it is only relatively recently that the progress in technology has allowed this restriction to be exceeded to the extent that in the twentieth century space coverings with spans of 300 metres and suspension bridges with a span of 2000–3000 metres were being constructed.

Wide-span hall roofs have some kind of supporting structure, which may bring the loads down into the soil, or be supported by separate supports such as masts, columns, frames. They also have a weather shield, which may be a membrane, panels laid on top of the supporting structure or a unified loadbearing and weather-shielding structure. As a consequence wide-span structures may be classified according to one of the three types of structure. This leads to overlapping classification systems since each of the three types of structure may be combined with various classes of the other two types of structure. A dome, for example, has one single structure with a load-bearing and weathershielding function and may be supported in various ways. A membrane may be self-supporting or suspended from masts.

The last 150 years have not only brought with them a gradual increase in span (and height) but also a considerable number of new structural schemes and architectural forms for covering spaces: shells, vaults, domes, trusses, space grids and membranes (Chilton, 2000). A great variety of domes have been developed: Schwedler, Kievitt, network, geodesic, and lamella folded plate domes.

Type of a Schwedler dome

Steel trusses were developed beginning in the nineteenth century. In the first half of the twentieth century reinforced concrete came on the scene as a competitor to steel for long-span structures, for instance in the form of braced or ribbed reinforced concrete domes and roof structures (designs by Pier Luigi Nervi, Eduardo Torroja and Felix Candela). During the 1920s and 1930s thin reinforced concrete shells were constructed. Shells may be not only domes but also cylindrical and prestressed tensile membrane structures. Then up to the present time, a great variety of new structures were added to the list of wide-span structures: steel, aluminium, timber, membranes, space trusses (with one, two or three layers, polyhedra lattices) and tensile (tensioned) structures (Karni, 2000). Another aspect of categorization is the way in which vertical loads are transmitted to the ground: directly by the structure, as is the case with some domes, or by special supports: pylons, masts or columns. In this second category are the ‘masted structures’ (Harris and Pui-K Li, 1996). A masted building may have one, two or more (four, eight, etc.) masts and these can be placed interior or exterior to the building. A special category is formed by rotational structures, which may have one mast, or several within the building envelope or, alternatively multiple masts may be arranged around the perimeter of the building. Some of such rotational structures may be designed for grandstands. It is obvious that the masts not least due to their conspicuous appearance influence greatly the overall architectural design and its details.

Some of the load-bearing roof structures require an external layer on top for water and heat insulation purposes. Competitors to traditional roofing materials (wood shingle, reed, clay tile, stone slab, lead, copper) made their presence felt: corrugated coilcoated steel or aluminium sheet, plastics, foil or textile, factory-built-up composite panel (Selves, 1999). Some of these are also applied as wall cladding or suspended ceilings.

As mentioned earlier, stadiums are increasingly being constructed with a retractable roof, which makes sports events feasible in any kind of weather: typical are the stadiums designed by the Japanese Fumihiko Maki and others. The year 2002 saw the USA’s first retractable football stadium completed in Houston. Here the travelling mechanism of the roof rides on rails along the tops of exposed structural steel super-trusses and during retraction the two trussed panels part in opposite directions. The wheels of the mechanism ride on a single rail. Each of the two 287 metre-long super-trusses is borne on two reinforced concrete super-columns, which are nearly 210 metres apart, thereby eliminating the need for columns in the seating stands (Engineering News-Record, 2000). Plans have been put forward to rebuild the London Wembley Stadium with a retractable roof and with a capacity of 90 000 seats. Other recent designs of retractable roofs demonstrate a number of innovative solution possibilities (Ramaswamy et al., 1994, Levy, 1994).

Sebestyen, Gyula. 2003. New Architecture and Technology.

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