The horizontally sliding cushions in the Gerry Weber Stadium allow the roof to be open, allowing fresh air and direct sunlight to penetrate.

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1 Jürgen Bradatsch, Peter Pätzold, Cristiana Saboia de Freitas, Rudi Scheuermann, Juan Monjo, Marijke Mollaert The horizontally sliding cushions in the Gerry Weber Stadium allow the roof to be open, allowing fresh air and direct sunlight to penetrate. Fig. 77 Gerry Weber Stadium, Halle, Germany Schlaich, Bergermann und Partner, Carl Nolte GmbH, Koch Hightex, 1994 (source of the image: Schlaich, Bergermann und Partner) A single skin cover for a swimming pool requires a high energy level input during winter since a relatively high internal temperature level needs to be maintained. The heating costs unfortunately are excessive. Fig. 78 Swimming pool, Paris, France R. Tallibert, Du Chateau, Stromeyer & Co, 1967 (ph. M. Mollaert) TensiNet I 81 I

2 Form Part of the inner courtyard of the City Hall in Vienna is covered by a movable membrane roof. The membrane s waves echo the neo-gothic styled arcades of the City Hall. The entire structure consists of longitudinally movable valley cables mounted on axial and radial rollers and running along a pair of rails. 3.8 Fig. 79 Covering of the City Hall Vienna Archcourt, Austria Architecture + Urban Design, Silja Tillner, covertex GmbH13 Qualities of Membrane Architecture As a building system, tensioned membranes have very special qualities, mainly as a result of their unique form and the nature of membrane materials. For these reasons they invite architectural solutions that conventional building systems cannot offer LIGHTWEIGHT Tensile structures are light in weight because their structural stability results from their prestressed shape rather than the mass of the materials used. Consequently, they are much lighter than conventional building structures yet offer high stability. The combination of low mass and wide span provides the architect with opportunities of expressing lightness and stability in a coherent and unified way through the organization and shaping of each detail. I 82 I Fig. 80 M.O.M.R.A Tent, Riyadh, 1994, SL Rasch European Design Guide for Tensile Surface Structures

3 Jürgen Bradatsch, Peter Pätzold, Cristiana Saboia de Freitas, Rudi Scheuermann, Juan Monjo, Marijke Mollaert TRANSLUCENCY Translucency is one of the most widely appreciated qualities of engineered fabric architecture. Indeed such translucency can provide the necessary amount of daylight for standard building usage, playing an important role in the building s energy efficiency. This is particularly relevant in buildings where light is needed in a plentiful and even ostentatious way, as for example in commercial architecture. Such translucency also offers great aesthetic possibilities for architectural design, through the use of natural and artificial light. At night the membrane s translucency can transform the structure into a sculpture of light. Fig sqm Assembly Tent, Malaysia, 1997, SL Rasch Translucency of a multi-layer membrane roof. The translucency of engineered fabrics depends on the type of fibre that forms its structural base as well as on the fabric coating material and colour. The translucency of standard membrane materials varies from 10% to 20% but there are also materials available with 40% translucency, while others are opaque. The level of translucency and the type of light within can also be adjusted by the use of pigmented coatings or printings. Even insulated multi-layer membrane roofs can be designed to be translucent by combining appropriate membranes with translucent insulation material. To the human eye such roofs appear bright and translucent even when the light transmission is only a few per cent, giving the appearance of a lightweight roof structure. TensiNet I 83 I

4 Form FLEXIBILITY Tensioned membrane structures are not rigid, they change their form under the influence of wind and snow. The membrane geometry responds to the applied loading by deforming, and in so doing develops smaller radii in the direction of the loading, and in turn finds a more efficient form for the particular load case. The flexibility of tensile structures allows large displacements to occur without permanent deformation. The degree of change and response depend on the elasticity of the material and the prestress level used for the structure. The structural intelligence of natural structures can inspire the architectural design process. Fig m x 10m umbrella with folding arm system, prototype, 1988, SL Rasch Umbrella is folding. Temporary erected in San Francisco, in front of UN building. The degree of flexibility varies for different fabric materials. There are highly flexible materials that allow folding without fracture or wear. Such materials are the basis and precondition for efficient mobile and convertible building structures. SCULPTURAL A tensile membrane s unique curved shape has a very strong sculptural quality. The tensioned surface finds equilibrium within itself. The up and down movements of an anticlastic membrane shape are balanced, and it is possible to create large buildings that seem to float effortlessly between heaven and earth, defying gravity. This sculptural quality is sensational, both outside and inside the building. Fig. 83 I 84 I Entrance arch at Federal Garden Exhibition, Cologne, 1957, Frei Otto Sculptural architecture and landmark for the exhibition entrance at day and nicht. European Design Guide for Tensile Surface Structures

5 Jürgen Bradatsch, Peter Pätzold, Cristiana Saboia de Freitas, Rudi Scheuermann, Juan Monjo, Marijke Mollaert Tensioned membranes give architects the possibility of creating dramatic and complex spaces that are balanced within themselves. These membrane sculptures dramatically change their appearance in the play of light and shade during the changing natural lighting conditions of the day. The low angle of the morning and evening sun accentuates the curvature and relief of the roof, and when the sun is at its apogee the flowing edges of the membrane cast curved shadows on the ground. Subtle artificial lighting arrangements using the translucency as well as the reflectivity of membrane materials to the best advantage can transform the membrane structure into a sculpture of light SAFETY Lightweight tensioned structures are safe structures designed and dimensioned according to such national codes and guidance notes as exist (see Chapter 6). Lightweight structures are particularly stable in horizontal loads like earthquakes. In an unforeseen case of collapse lightweight structures tend to be less dangerous than conventional building systems because of their much lower mass. The risks are even smaller when the layout of the tensioned structure guarantees that stiff supporting elements, like masts and beams, will not collapse should the membrane tear. The flexibility of membrane structures allows them to find a more efficient form for a particular load case. However the structure s layout and form needs to be developed and tuned for such situations. The designer should ensure that the membrane and all its associated components work together sympathetically so as to avoid the creation of a critical concentration of singular forces within the membrane surface or its attachments FUNCTIONS While the qualities of tensile structures can be suitable for a wide variety of architectural functions, from simple shading roofs to complex design briefs, there are some functions to which they are particularly suited EXPRESSIVE ARCHITECTURAL FORM An architectural function common to every building is that of representing an idea. The unique shapes of tensioned membrane structures present a natural beauty that is in itself an architectural statement. Such forms create interesting landmarks, in themselves as well as by their juxtaposition with conventional buildings. Well designed membrane structures are struc- Fig. 84 Sail Island, Jeddah, 2001, SL Rasch Expressive form and landmark at the Corniche at Jeddah. The design idea is a reminiscence of sailing ships. TensiNet I 85 I

6 Form turally and formally well balanced, making them stand out and allowing easy integration within both natural environments and manmade urban environments, be they historic or modern. Lightweight structures can be designed and seen as large sculptural elements, bringing to life the spaces around them. By design they can complement or act in counterpoint to their surroundings. Fig Dynamic earth centre, Edinburgh 2000, Hopkins Architects. The contrast between the natural tensioned forms and the conventional building can be used as an urban design element to define urban references in city centres. WEATHER PROTECTION One of the main functions of a roof is to provide shelter and comfort in weather conditions such as sun, rain, wind and snow, depending on the particular climatic zone. The choice of membrane shape and material should take into account all appropriate conditions so as to provide a suitable internal environment, wherever possible by passive means using the architecture itself to reduce the building s energy consumption. Membrane materials with a porous open structure can be used for shading. This gives some control over the transmission and reflection of sunlight, so as to bring diffuse light into the space within and stimulate natural ventilation. This in turn can keep the surface temperatures at the level of the ambient air and avoid downward radiation of heat. For protection from rain and snow, the form should allow fast and easy drainage of water and snow. The ponding of rainwater and large accumulations of snow on the roof have to be avoided. Tensile membrane structures are particularly susceptible to these kinds of loading during the erection stages until the final form and prestress have been established. To keep rainwater out, the membrane material and its joints have to be closed and tight and the edge has to be detailed very carefully to prevent water getting inside the envelope. I 86 I European Design Guide for Tensile Surface Structures

7 Jürgen Bradatsch, Peter Pätzold, Cristiana Saboia de Freitas, Rudi Scheuermann, Juan Monjo, Marijke Mollaert Fig. 86, 87 Modular Assembly Tent, SL-Rasch and Jürgen Bradatsch with Frei Otto, Malaysia, Tent developed as a mobile, modular structure to provide optimal climatic comfort conditions for tropical climate. Among the specific design solutions, the architectonic shape was combined with the fabric s thermal proprieties to avoid excessive radiation transmission and to increase the natural ventilation under the membranes. The external membrane layer is done with an open grid fabric, avoiding excessive radiation on the second membrane, which is waterproof.fig. 00 Tekst tekst bla bla bla bla bla bla bla bla TensiNet I 87 I

8 Form MOBILE AND TEMPORARY The lightness of tensile structures gives them a clear advantage over other constructions when they are considered as a reversible intervention on the environment. Two other important aspects are mobility and flexibility. Designing a structure that can be erected again and again and at different places is the expression of a tensile structure s mobility. Such structures can be a synthesis of the nomad tent and the permanent settlement. The lightness and flexibility of the material permits these structures to be carried and deployed easily and quickly yet occupy a modest volume when not in use. These characteristics are useful for temporary and mobile structures, and are essential in the case of catastrophes and emergencies when shelter is required for a great number of people in a short time. Fig. 88 Starwave tent for La Biennale di Venezia 1996, Frei Otto, SL Rasch. Mobile structure for exhibition with heavy weight temporary foundations. On the other hand, the design of mobile structures that are able to provide a comfort level equivalent to that of permanent buildings opens a new aspect in the construction field, once the ownership of a building is separated from the ownership of land. The building becomes movable instead of being immovable. This is of great importance in the accelerated development of today s cities, and in the consequent changes of use in particular zones, since such buildings can be moved and reused. I 88 I European Design Guide for Tensile Surface Structures