Technology

Tensile constructions in modern architecture

MEMBRANES & ETFE FILMS 

Compared with the well-known and proven construction materials stone, wood, steel, concrete and glass, membranes and ETFE films are a relatively young product in terms of construction history – even though our ancient forefathers already had the idea of covering their homes and supplies with animal skins and later with hand-woven materials to protect them against the elements.

Today, membrane and ETFE architecture – also known as tensile architecture – is a highly developed technology that is used for constructions as diverse as pavilions, building facades and roofs– it has proven to be not only a reliable construction element but also an innovative architectural design element.

By definition, membranes and ETFE films are thin, stretched films, similar to the eardrum or the wing of a bat. Countless other forms and regularities found in nature have inspired architect Frei Otto and his team to research the foundation for a new structural technology and to develop it further for practical applications.

Aside from a plethora of new developments in construction technology, lightweight structures developed out of membranes subject to tensile loads which ablate loads from wind and snow through the oppositely curved (anticlastic) shape of its surfaces. Textile structures are mostly three-dimensional supporting frameworks, consisting of a combination of supporting elements created from membranes, steel and cables. The latter are used to support the mounting and tension of the membrane. The easiest and classic basic form is the so-called four-point canopy. Its typical form resembles a saddle.

FOUR POINT CANOPY

Air domes or cushions are other frequently used membrane structures supported by air. These equi-directionally curved (synclastic) forms are stabilised by means of positive air pressure.

On the material side, coated fabrics have proven reliable. The fabrics mostly used are extremely tear resistant polyester fabrics with PVC coating and extremely tear resistant fibreglass fabrics with PTFE coating, as well as ETFE films used as pneumatic mutli layer cushions or tensioned in single layer configuration. The application determines the quality of the material chosen.

Quality is defined by the most important properties: tear resistance, low weight, high transparency, durability, fire behaviour and longevity.

FabricsPES/PVC
Acrylic finish
PES/PVC
PVDF finish
Glass/PTFE
Average lifespan10–15 years15–20 yearsOver 25 years
Weather resistancexxxxxxx
Dirt resistancexxxxxx
Transluzencyxxxxxxxxx
Fire behaviourxxxxxxx
Crease resistancexxxxx(x)
Costs (base value: 100)100110200/250
Places of applicationTemporary and
permanent 
structures
Temporary and
permanent
structures
Permanent
structures

EVALUATION RATING:

(x) = unadequate; x = adequate; xx = good; xxx = very good Just as with conventional construction, the planning of a membrane structure is an interdisciplinary interplay between building owner and user, architect, engineer and contractor. It is vital to know the structural requirements and the factual and technical correct properties and possibilities of membrane constructions. Advanced calculation software helps to design its shape, to calculate its static and to plan further details – a great tool allowing secure and economic project management. The planning phases are almost identical to those completed for conventional construction project.

The installation of a membrane structure is carried out by means of an assembly method: individual structural elements are prefabricated in a manufacturing plant and assembled on-site. Membranes are made-up in the plant: they are cut from a flat piece from a fabric roll and are welded into the pre-calculated, three-dimensional shape. This includes all details needed to mount and pre-stretch the membrane.

IDEAL APPLICATIONS FOR MEMBRANE TENSILE ARCHITECTURE

Textile fabrics made of tear-resistant polyester, fibreglass and ETFE films open up a new dimension in construction. Thanks to their high flexibility, their low weight per square meter yet high tensile strength and their transparency, it is possible to:

  • cover great surfaces without support columns
  • design rooms and spaces that are bathed in light
  • realise completely new construction shapes
  • create a memorable view thanks to design and colour
  • set up temporary structures and buildings that can be reused at other locations
  • construct efficiently with only as few resources
  • open up completely new construction areas

The possibilities with this construction method are extremely versatile. Membranes and ETFE, mostly realised as roof or façade structures, provide lasting protection against the elements – and much more than that. Multi layer tensile membranes and ETFE air inflated cushions possess a high insulation value and added sound insulation. Aside from membrane constructions with added thermal insulation, membranes can be realised with high transparency or completely opaque. Plastic coated polyester fabrics are available in all colours, while coated fibreglass is mostly white. White or bright colours are often chosen because they are visually pleasant and feature an optimal transparency.

CURVED ROOF MEMBRANE

HIGH-POINT ROOF MEMBRANE

Even with the limits that the laws of physics impose on membrane construction, the formal design possibilities of membrane architecture are still extremely diverse. The choice of the membrane shape is often not only determined by the functional requirements but by an architectural and design background. Frequently the marketing concept of the client plays a role in the choice as well. That is why a well-executed membrane structure can play an important role in the creation of the image of a building or a company.

Plastic coated polyester membranes are the ideal choice for temporary use. The low weight and the flexibility of the material make the assembly and disassembly of the structure easy and simple. Retractable roofs – roofs that open and close automatically – are exclusively made out of plastic coated polyester fabric as well.

Costs are an important factor when making the choice for a specific construction type. In classic construction, there is still no construction that's the least expensive one regardless of its use. The same is true for membrane architecture. In general, membrane constructions are financially feasible when large spans or areas need to be covered or when the construction features a large degree of repetition.

An important piece of advice: membrane as a material have not been generally approved by Germany's building authorities. Instead, an approval must be sought in each individual case. Even though this process is becoming more and more of a routine exercise, unwanted delays can occur if documents and paperwork are not prepared properly.

MEMBRANE AND ETFE ARCHITECTURE TODAY

Membrane and ETFE architecture has developed into a very popular high-tech construction method. The following sections aim to give an overview about current trends and the areas in which membrane architecture is frequently used – and why. Like in the past, today's textile structures are more and more present at locations where people spend their spare time.

Membrane structures with their unique, often playful shapes are not only lightweight and bright; they convey an inviting feeling of freedom and joy. Experience shows that indeed most people enjoy the atmosphere under a membrane roof. It is often a creative idea or an inventive thought that leads to success with something that is not an everyday occurrence. Membrane architecture has taken a permanent place in construction technology, as its many practical applications confidently demonstrate. 

CULTURE

Lightweight structures made out of tensile membranes or ETFE air filled pillows are the ideal solution to protect audiences of theatre plays and concerts against the elements. Events in amphitheatres are technically and financially challenging, so they need to be able to be put on without having to worry about the weather – that's why they are preferably covered with a canopy. Assembly and disassembly of a mobile roof are relatively simple and make this solution the solution of choice for cultural summer events. There's no need to calculate and prepare for a snow load on the roof – solutions are relatively lightweight and economic. Membrane architecture is well suited to protect monuments, museums and even to construct permanent theatre structures. Thermal and acoustic insulation solutions are easily available. Not only does the building owner profit from a functional construction, but the construction also serves to create an excellent outward look and appearance.

Implementation example
Musical theatre: Musical theatre "The Lion King", Hamburg, Germanyg

TRAVELLING

Membrane and ETFE constructions that cover airport terminal buildings, train station halls or bus stops are more than just an alternative to roof constructions made out of metal or glass. At these locations where people meet each other every day, architecture needs to be something special, joyful even. The lightness of the structure and its interplay with the sunlight creates excitement and acceptance. The material choice is especially important: in order to prevent the membrane surface from becoming dirty too quickly and to raise the fire resistance, PTFE coated fibreglass is the right choice.

Implementation example
Airport: Denver Airport, USA 

SPORTS

For more than 30 years, membrane roofs have been planned and implemented in stadiums and sports arenas. Even though the Olympic Stadium in Munich isn't a membrane roof, it belongs to the family of lightweight structures. At this stage, there are quite a few successful sports arena roofs that follow the concept of the lightweight principle of three-dimensional, membrane covered cable structures. The fascination with lightness of structure and shape and the low construction weight are convincing ever more architects and building owners. Membrane roofs can be built across large spans without the need for support columns. Support columns that would otherwise infringe on the view of the visitors who want to enjoy the sports event pleasantly and protected against the elements. Visitors of ice rinks also want to enjoy their favourite sport on days when the weather is bad. A membrane roof makes sure that this is possible and helps to save energy to boot. In the last recent couple of years ETFE has become a first choice material for the design and construction of sports stadia and arena.

Implementation example
Stadium: Mercedes-Benz-Arena, Stuttgart, Germany and Altanta, GA, USA

ARCHITECTURE

Architects are engaging more and more with the topic of membrane structures and are learning how to integrate them as complex structures into their overall concepts. Membrane architecture is mostly used as roof construction above entrances, terraces, but can also be a solution to cover a backyard or a façade. Covering carports with membranes is an idea often discussed among architects that has been realized successfully numerous times.

Many architects combine glass and membranes more frequently. This creates an interesting interplay between transparency and translucency – a living, always changing theatre of light.

Generally however architects need to catch up somewhat in their knowledge of membrane architecture. Not all colleges and universities treat this construction method with equal importance.

Implementation example
Membrane and glass: Sony Center, Berlin, Germany

SHOPPING CENTRES

Not just since yesterday has shopping become more than just buying the bare necessities for many people. Instead, they spend more and more of their increasing spare time in shopping centres which have turned into a recreation centre of sorts. No surprise, then, that architects and building owners are investing more money and effort into making these shopping centres even more attractive and inviting. Tensile membrane and ETFE air filled pillow architecture is a welcome concept to improve the construction design and the ambience of a shopping centre. Once again, the playfully designed arrangement of shapes and the transparency of the material score big with visitors. Its potential for indirect lighting and the soft glow of a membrane structure at dark are elementary features of this architecture.

EVENTS

Whenever a special event such as a World Expo, Olympic Games or a World Cup draws closer, its organisers at least investigate if a membrane or ETFE construction could create something unique and special. Construction time and cost are the most important factors – and with tensile membrane architecture it's possible to realise building structures, roofs and halls in a very short time. An easy and clear concept and a material choice that suits the intended use of the structure are prerequisites of an affordable solution. Should those constructions be used only once, a plastic coated polyester fabric is recommended. Meanwhile, some building owners and municipalities have opted to buy a mobile roof structure that can be used for one or more events or during the summer but will disappear into storage for the rest of the year.

Implementation example
Millennium: Millennium Dome, London, UK

MARKETING

For the marketing of prestigious consumer goods such as cars, the cultivation of an image plays a pivotal role. That's why membrane & ETFE architecture can be seen frequently in this segment. Cars are not only presented in an exciting atmosphere but protected against dirt and hail. Even during the winter, the cars are not covered in snow or iced shut. Marketing agencies frequently incorporate membrane architecture in their even concepts.

Implementation example
Trade show pavilion: Coca-Cola, Olympic Games London 2012, UK

MEMBRANE ARCHITECTURE TOMORROW

We can expect that architecture and construction technology will continue to advance and that the need for new ideas will only grow – a great chance for membrane / ETFE architecture to gain more influence and become more important. 

NEW MATERIALS

Aside from the proven materials, new and forward-looking materials are needed that fulfil technical requirements even better and that develop membrane architecture even further. Cheaper materials need improvements in their surface quality: dirt resistance and the ability to weld different segments together need to increase. Transparency should be optimized even further – some customers already ask for rear resistant, transparent materials. Another aspect is the environmental sustainability of the materials and their disposal. One promising development is the organic photovoltaic (OPV) integrated into ETFE films. It would allow freedom of design and colors while still producing electric power. A great tool toward energy sustainability and LEED or BREAM certification.

NEW APPLICATION FIELDS

Spare time will continue to go up, while the entertainment and sports business will gain in importance: more people will want comfortable stadiums with either a partial or full roof. Sports venues and arenas in Europe are lagging behind. Many stadiums are completely outdated and can barely accommodate today's events. The need for new stadiums with spacious roofs is big.

The transportation sector continues to grow. There's almost no European airport that doesn't feature some kind of construction: new parking structures, terminals and office buildings rise in front of our eyes – and all need to be covered. Likewise, train traffic will be expanded – with that comes the need for new stations and stops. Airships for the transport of goods will see a new boom (see: Cargolifter) which will cause huge investments in hangar and warehouse construction. An airship needs a building with huge spans – a need that is perfectly met by a membrane construction.

To celebrate the millennium, the world's biggest membrane construction saw the light of the world. Seeing its size and possibilities, we can only imagine the many exciting and diverse applications for membrane and ETFE architecture in the future.