Construction & bearing structure elements
Textile architecture making special demands on construction, material and design.
The fact that it is possible to freely roof large areas is a great advantage provided by textile architecture. For this purpose, membranes must always be held under tension.
Membranes can only be subjected to tension but not to pressure. In order to obtain the desired and statically calculable stability it is mandatory to apply a mechanical pre-tension in connection with an anticlastic design. The more the membrane is deformed, the lower the pre-tension forces to be applied, such forces resulting ultimately from the outer load through wind and snow in the framework of the static calculation.
Traditional basic forms of mechanically stressed structures are for example high point surfaces, canvas and arched surfaces.
The cost effectiveness of membrane structures strongly depend on their shaping. The more they are deformed the lower is the load on the bearing structure through pretension and the resulting forces of wind and snow. Adequate shaping makes it possible to achieve unsupported spans of up to 100 m.
Unfortunately, it is often inevitable to accept compromises due to constraints imposed by building regulations. Supported by suitable form finding programs, CENO engineers will always be pleased to assist you in finding the most efficient solution.
Bearing structures consisting of steel and steel ropes: The backbone of "Lightweight plane load-bearing structures"
In his dissertation on the subject „Das hängende Dach“(The suspended roof) Prof. Frei Otto developed his structural law as follows: "The use of high-quality building materials in an economic way and the utilisation of the bearing properties of spatial systems will create light, mobile structures of insignificant weight. The construction will be reduced to the absolute minimum required."For this purpose it is advisable to plan membranes and bearing structures in an integrative manner. This is the only way to develop cost-effective and at the same time architectonically appealing, filigree buildings. Apart from its covering function, the membrane assumes static tasks relieving the bearing structure. This is obtained through the shaping and the enormous strength of high-tensile textile fabrics. Having a comparable specific tensile strength as steel, the approximate weight of the membrane amounts to just 1/5 of the weight of steel. The advantages of the steel bearing structure are underlined by a multitude of variations using suitable connection details and by the possibility of pre-fabrication by the manufacturer. Cable structures provide additional aesthetic and economic aspects although this possibility may be limited by the floor space required for the bracing.
Air-borne structures as an alternative:
Apart from mechanically pre-stressed membrane surfaces, pneumatically pre-stressed - i.e. air-borne - cushion constructions, particularly made of ETFE foils have increasingly been used over the past years.
For the required nominal geometry of the cushions, the upper and lower foils receive cut blanks guaranteeing a taut upper and lower surface at an internal overpressure of 300 to 800 Pa even in the case of extreme loads. Due to the low basis weight of the cushions, the bearing structure's design can be very filigree and light. Using aluminium frames, the cushions are mounted over large roof and facade surfaces on the bearing constructions made of wood, steel or aluminium.
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