tensile structures in architecture
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11 May 2009 Understanding Complex Structures
Webs, nets and tensile structures in architecture
Professor John ChiltonSchool of Architecture, Design and Built Environment
Nottingham Trent University
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Introduction
Content:• structure and pattern in nature• grids and gridshells• cable nets• tensile fabric structures
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Venus flower basket (Euplectella aspergillum) Siliceous glass sponge, 30cm(courtesy Ture Wester)
Courtesy Ture Wester
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Complex spatial grids (nets) can be assembled from steel components such as the Mero bar and node system developed specifically for the new Milan Fair canopy (2005).(Architect: Massimiliano FuksasEngineer: Schlaich Bergermann & Partners)
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Examples of Radiolaria from Häckel, Art Forms in Nature, 1974
Courtesy Ture Wester
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Sometimes emulating a bird’s nest is more difficult.
Beijing Olympic Stadium (2006)Architect: Herzog & de MeuronEngineer: Arup
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‘Woven’ tensegrity structureFinal Examination Project, DTU 2002: C. Lundstrøm & A.P. GalsgaardPhoto: Ture Wester
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Photo: John Chilton
Spider’s webSpiral or orb web - filigree net of tensile threads
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Kibble Palace, Glasgow (original Coulport, Loch Long early 1860s, on present site 1872/3)Filigree net of glazing bars, stabilised by the glass
Timber gridshells at the Earth CentreDeformed square grids stabilised in double-curved form by diagonal cables
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Millenniium Dome (O2 Arena), London (1999)Suspended cable net on domed form covered with tensile fabric (PTFE/glass)Architect: Richard Rogers; Engineer: Buro Happold
Sony CentreBerlin, Germany, 2000
Architects: Murphy & JahnEngineers: Arup
Basic shapesAnticlastic tensile structures
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Generally for stability architectural tensile cable net and membrane structures have anticlastic double curvature. However, curvature can be synclastic for inflated membranes.
Olympic Games stadium, Munich, Germany, 1972Architects: G. Behnisch & F. Otto; Engineers: F. Leonhardt & Jörg Schlaich
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Typical formation
Coated woven membranes
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For tensile membrane structures a woven fabric (e.g. polyester; glass) is substituted for the cable net and this receives an impermeable coating (e.g. PVC, PTFE, silicone, PVDF) which is usually translucent.
Design process for architectural membrane structures
• Select boundary conditions– support locations– edge details– pre-stress to be applied
• Form-finding of surface shape using e.g. – dynamic relaxation – force-density
• Determine stresses in membrane under service conditions (e.g. snow, wind loads) using structural finite element analysis software
• Select appropriate material
• Fabrication and installation– Patterning– Cutting of fabric – Radio-frequency or heated bar welding (usually) – assembly into fields– tensioning between boundaries
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WEST ELEVATIONSOUTH ELEVATION
PLAN VIEW
Boundary Conditions – support for membraneInland Revenue Amenity Building, Nottingham( Architect: Hopkins Architects; Engineer: Arup)
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Form-finding (Technet Easy) Structural analysis (Technet Easy)
Patterning (Technet Easy) Cutting pattern (Tensys)
Photograph: John Chilton
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Form-finding with physical modelsUsed for early cable nets and can also be used (following inversion) for pure compression structures (e.g. reinforced concrete shells)
Petrol station canopy, Deitingen, Switzerland , 196831.6m Span/thickness ratio ~400:1
Photograph: Heinz Isler
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PTFE coated glass fibre fabrics
+ Chemically inert+ Lifespan >25 years
- Very stiff (more difficult to handle/detail)- More expensive- Not suitable for deployable structures
PVC coated polyester fabrics
+ Cheaper+ Flexible
- Tend to discolour with time- lifespan 10-15 years
Typical materialsCoated woven Membranes
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Cutting PatternStadium roof in Abuja, Nigeria showing patterning of membrane surface (Form TL). This has an impact on the aesthetic of the architectural envelope
Tensile membranesBy their nature tensile membrane structures are designed to cover large areas with lightweight material (commonly around 1 kg/m2).
They are also designed for ease of dismantling, as the surface has a design life of typically 15 to 25 years after which it needs to be replaced.
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Tensile membranesDuring installation the prefabricated membrane is suspended and pre-tensioned using (normally) steel components (such as edge cables, bolts, plates etc) attached to steel masts and tie-downs.
Dismantling directly reverses the erection process. PVC/polyester membranes can be fully recycled.
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http://www.texyloop.com/internet/gb/
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More information on tensile fabric architecture:www.tensinet.comwww.architen.comwww.formfinder.at