Membrane constructions only withstand tensile stress due to the low compressive and bending rigidity of their surface. This principle is optimized in double curved constructions. In contrast, plane surfaces react sensitively to deformation by external loads. They tend to flutter and create snow and water-traps, which in extreme cases can lead to a failure of the construction. This means that the stabilization of plane areas requires high pre-stressing. The design and draft of tensile constructions follow completely different principles to other supporting structures. The main difference is that the design process of tensile membrane constructions mostly develops self-regulations. This means that either the form of the membrane approaches the so-called “minimum surfaces”, or it is influenced by changing the boundary conditions respectively by inserting additional supporting elements (which can be linear, plane or pointed). This allows the creation of either “anticlastic” saddle shape surfaces or “synclastic” surfaces when using pneumatic internal pressure like a balloon. Supporting media for producing internal pressure can be air, gas, water or other liquids but also granulated materials. A completely freely invented design form therefore must be compelled with the help of additional compression and/or bending-stressed carrying elements.
The minimum surface approach means following physical principles under the condition of similar surface stresses within defined continuous edge elements. The stress demands put on the membrane surface will determine the construction and the patterning of the edges, tension elements and anchors. Whereas soap skin models, for example, were used in the early days of tensile architecture, today computer generated models are applied for accurate dimensioning and automated cutting. The structural analysis must be completely integrated into the architectural design. The geometry of the membrane is established using a shape generation (form finding) technique in order to ensure the static equilibrium of the system.
First of all, a shape generation technique must be used to establish the natural equilibrium shape. The equilibrium shape is the geometric configuration which induces a static equilibrium with its own internal pre-stress forces. Having a stable configuration, the structure is analyzed under various load cases using finite-element analysis software. These programs permit the inclusion of tension-only membrane elements, as well as cables, struts and beam elements in a three-dimensional computer model resulting in rapid, accurate analysis and sizing.
Each batch of fabric is tested in a biaxial (both direction) mode, to measure the stretch in both thread directions at load ratios derived from the form generation computer model. These figures are then used as “compensation percentages” that are factored into the patterning software. The fabric is deliberately manufactured undersize so that it tensions out correctly when installed to its final dimensions. MEHGIES® vario-stretched material properties have been perfected to meet the engineers’ requirement in reacting to force distortions generated by orthogonal loads.
The construction design has also developed over time, using more advanced materials and construction methods to produce larger and more diverse structures such as the European Championship Stadium in Posen, Poland. Modern fabric materials in modern architecture can shape space, enabling architects to sculpt 3-dimensional areas in a manner that is not possible with any other type of material. This kind of architecture offers much more: the designer is able to play with light and use it to naturally illuminate the space, soften it, fuse it, sharpen it or shape it. This creates a mood and ambiance to reflect the architectural intention, resulting in an energy saving covering system while approaching the elementary need to be in touch with nature. The dynamic shapes and forms of membranes allow new possibilities in stimulating the architect's imagination.