The art of building is indivisible!

Maurizio Scalera

This motto, which states the principle governing the work of SBP (Schlaich, Bergermann and Partners) Structural consulting engineers, clearly characterized the February lecture of the German professor J�rg Schlaich. He truly affirms: 'our curiosity knows no boundaries' and began his speech by introducing the idea of light-weight structures as a social, ecological and cultural way of building.

The primary theory is the principle of scale, by which, increasing the span, it consequentially increase the volume of the construction and obviously its weight. The use of high-performance structures on the other hand reduces the size of the sections, so they become material-efficient and therefore ecologically and socially suitable. At the present time, the amount of energy spent to produce 'hi-tech' materials is still very high and a particularly skilled craftsmanship is necessary to assemble them. Thus the light-weight structures end up more expensive compared to 'traditional' construction processes.

He presented a table where the different structural systems are classified in relation to the physical geometrical principle and the materials employed to generate them. The sequence of items follows a virtual uprising parabolic curve. It begins with culturally consolidated constructions (such as the pedestrian bridges) moving toward very complex and sophisticated systems, like the freeform glazed grid shells with flat quadrangular meshes generated using the principle of translative surface (Schluterhof Roof, German Historical Museum).

Since the prefatory lines it is evident that the work of J�rg Schlaich, and his steadfast team of designers and researchers based in his consulting office and in his Institute for Conceptual and Structural Design at the University of Stuttgart, is impressively wide and varied. It combines scientific research, pragmatism and meticulous attention to the details, with a concern about the relation between the natural and the anthropic environment, probably without limits within the spectrum of utilitarian structures and engineering applications. His cultural background is from the theoretical, Berlin-based tradition of Franz Dischinger and the pragmatic, experimental 'Stuttgart' tradition of Emil M�rsch, maintained by his mentor Fritz Leonhardt, and of course the geodesic dome theories of Richard Fuller and their applications by Felix Candela, without losing sight of his long collaboration with Peter Rice (to whom the lecture is dedicated).

Since the late Sixties, Schlaich and his partners have designed, analyzed, checked and supervised a wide range of innovative structures comprising pedestrian bridges, highways and railways bridges, glass-fibre reinforced concrete hypar shells, glass-grid roofs freeform or dome-shaped, cable-net structures, textile membrane roofs and revolutionary solar power plans. Particular attention is given to the analysis of all building materials, either 'traditional' like steel, concrete and wood or 'new' such as light alloys, composite elements, glass, membrane, their intimate nature and the respective jointing technologies.

For the first time they allowed a renaissance of cast-steel in modern structural engineering. Utilized for example in the roof of Munich Olympics Arenas (1972) where the numerous saddles and joints with ever changing geometry could never have been realized without a new type of styro-foam forms for cast steel, or in the joints of the tubes and their connections with the concrete deck and the piers in the Humboldthafen Railroad bridge.

The development of the new material Glass Fibres Reinforced Concrete (GRC) is also very interesting in which alkali-resistant glass-fibres are gunnited or mixed with the mortar resulting in a concrete that, in addition to its compressive strength, has a permanent tensile strength, and therefore appears to be ideal for shells like the one in the Garden Exhibition in Stuttgart (1977). Another new material used widely by SBP, especially in wide-span roofs of sport facilities or stadia, is the PTFE-coated glass-fibre membrane which offers several advantages against other materials: its limitless variety of shapes, its lightness also for large spans, quick and easy to assemble, dismantle and recycle, and the possibility of being a translucent fabric. On the other hand the costs are high and it doesn't last more than twenty-thirty years. With the PTFE they realized the roofs, among other projects, of Seville Olympic Stadium (1999), NSC Competition Pool and Outdoor Stadium in Kuala Lumpur (1997), Pusan Dome (2001) and the Frankfurt Stadium under construction (expected completion 2005).

During the lecture he explained some principles behind his structural engineering applications by showing some apparently simple every day life examples. An ordinary wire kitchen sieve in reality is a sophisticated double-curved surface, made from plane square wire mesh and receiving its dome shape merely by changing the mesh angles. This geometric trick, combined with a stiffening cable-net structure, permits one to obtain the ideal shell, whether made in concrete, glass-grid or textile membrane, which is very light and efficient from a structural point of view (Museum Courtyard roof, Hamburg). Even the spoked wheel is a highly intelligent structure. The rim, soft by itself, becomes surprisingly stiff with the addition of thin pre-stressed spokes. Therefore this stratagem can be applied to a larger scale becoming a transparent diaphragm for the stiffening of tubes (cable net cooling towers and solar chimneys) or of cylindrical light-weight glass or membrane roof which absorbs the transversal loads acting from the rim to the hub (glass roof for DG-Bank, Berlin).

Also extremely important is the research made by SBP and the University of Stuttgart in the field of natural power, which has led to the application and production of new devices for the harnessing of solar power. The dish-Stirling system consists of a large parabolic mirror that concentrates the solar radiations onto a small heating surface with little tubes where a gas is heated to a temperature of almost 700�C which drives a Stirling engine generating electrical power. The new special features of this system are not the scientific principles, but the construction methods that make very large and accurate concentrators possible by the development of the stretched metal membrane technology with a thickness of just 0.5mm. Another new solar power system is based on consolidated physical effects proven over centuries (such as the greenhouse, the chimney and wind turbines) is the solar chimney: a bed of black ceramic gravel is situated under a glass roof where hot air is produced by the heat of the sun. This flows through a chimney placed in the middle of the roof and is drawn upward driving turbines installed at the base which produce electricity. One prototype has been built in Manzanares, Spain (1989), but there is already a proposed project, to be realized for 2005 near Mildura (Australia), for a one kilometer high solar chimney, which will be the tallest human-made construction on the planet, capable of 200 Megawatt power production, enough to fully fuel a middle size regional town, with an estimated cost of 700million dollars.

After the lecture of the German professor I was certainly fascinated by his projects and constructions, but above all by the future scenarios he depicted of the energy produced by solar power plants. However I am ultimately unconvinced of the value of these highly sophisticated systems. Of course I do not doubt their efficiency and constructive ability but it seems that the light structures theory has an intrinsic dichotomy in its nature, and therefore in its aesthetic: their purpose is lightness and transparency, which are not always simply synonymous of quality. These constructions try to be each time ever more diaphanous that so one day they would virtually disappear from sight while their presence is firmly there (eg Hotel Kempinski at Munich Airport). The aim is to obtain the maximum continuity between different spaces, from inside to outside, from private to public, from natural environment to artificial places. These technological surfaces often represent a strong boundary which separates opposite contrasts or creates different microclimates and habitats, so why should they want to cease to be visible?

Here, in my opinion, is the main paradox- more virtual continuity generates more physical separation. Instead of obtaining this idealized lightness, it often happens that the medium overcomes the meaning, and so we observe the fragmentation of the structure (for example cable-nets and sharp joints) which loses its plasticity, its materiality, its "taste" and, above all, the natural hierarchy of the elements implicit in its construction.

So hopefully architecture will never become just a transparent membrane between different climatic conditions�

Maurizio Scalera is an architect, graduated from University of Florence in 2000 and is working with Grafton Architects.