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

john.chilton@ntu.ac.uk

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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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Geodesic domeDali Museum, Figueras, Spain

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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

• Cutting• Welding• Assembly into field

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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