Designing dynamic membrane structures is harder than it looks.
By Mark Zeh
One of the enduring visions in the use of membranes and fabrics in architecture is that structural volumes can dynamically respond to people and the environment. This vision is of buildings that can expand, contract or otherwise change shape for different uses and allow weather and light in as desired.
There are three basic categories of these dynamic types of membrane structures: adaptive, kinetic and convertible (most common).
Projects such as the 1996 “Airquarium” Airtecture Display Hall from Festo, which could adjust its stiffness in response to environmental loads, and the 2001 GINA concept auto from BMW Group Design, are examples of different types of adaptive structures. These applications show how membrane technology can allow forms and surfaces to change, depending on what outcome is desired.
Kinetic membrane structures are those that change shape, or move, to evoke a response. They are most often seen as art or concept pieces. One example is the 2001 Expo.02 Nouvelle DestiNation in Biel, Switzerland, by Eckert Eckert Architekten of ZÃ¼rich, in collaboration with the German artist Via Lewandowsky, which continually altered its form as a way of engaging visitors in a dialogue about politics in Switzerland. Another example is the 2003 GEK Balance Roadshow, designed by Schienbein + Pier GbR of Stuttgart, Germany. This demountable membrane structure was designed to give attendees the experience of traveling through the interior of the human body. It was composed as a reconfigurable modular structure of organic volumes, because it had to be assembled in many different venues.
A structure such as the National Stadium in Warsaw, Poland, from gmp (von Gerkan, Marg and Partners) of Germany, built for the 2012 UEFA cup, embodies state-of-the-art design and construction of convertible structures. According to gmp, it is the largest flexible roof in the world. It consists of a complex, tensioned cable-supported 55,000m2 PTFE/glass fixed membrane roof with an 11,000m2 PVC/polyester fabric retractable roof at its center.
Another convertible roof example is the 2003 Giesshalle H01 in the Landscape Park Duisburg North in Duisburg, Germany. This structure was rebuilt as weather protection for open-air events during the Ruhr Triennale by planinghaus architekten bda, of Darmstadt, Germany (opposite). Uwe Burkhardt, of Schlaich Bergermann und Partner, explains that since PVC/polyester, a material that can be folded, did not meet the transparency requirements of the design team, the solution created used pressurized ETFE cushions in metal-framed “carts.”
A long history of development
It is worth exploring why convertible roofs are, by far, the most-commonly seen dynamic type of membrane structure. This type of roof has the longest period development: Retractable sunshades in amphitheaters and stadia antedate by some time the velarium at the Roman Colosseum. Modern structural techniques and materials have enabled this concept to evolve from that of a retractable sunshade into a retractable fabric roof that shields against weather and can be opened to sunlight and fresh air. Development in the last 30 years has been amazingly fast, providing obvious benefits for event promoters, facility owners and the public.
Why haven’t we seen a similar push toward “design maturity” in the other two categories?
“I think most architects have lots of these ideas in their sketchbooks,” says Tim Hupe, founder of Tim Hupe Architekten in Hamburg, Germany,“but membrane projects with dynamic components can’t be attempted without a really great engineering partner, and the project costs are usually high.”
“There really are only a handful of companies that can engineer a dynamic membrane structure,” says Prof. Dr. Jan Cremers, director of technology for Hightex GmbH of Rimsting, Germany. “Also, architects who haven’t been taught in membrane architecture need to do quite a lot of work to understand the technical constraints of the technology.”
Several room acoustic solutions using membrane materials are on the market, from companies such as Birdair Inc. of Amherst, N.Y. and Koch Membranen GmbH of Rimsting, Germany. However, sound transmission through membranes remains a major challenge.
“High frequency sound is reflected by many materials used in membrane architecture,” explains Dr. Rosemarie Wagner of the Karlsruhe Institute of Technology, Germany. “But low frequency sounds pass through most membrane walls with little attenuation. You can see an example of how this problem can be resolved at the Bangkok airport, where an additional layer of fabric was suspended beneath the membrane roofs to trap the low frequency sound from the jet engines.”
Another challenge is energy loss through membrane materials.
“The materials are quite thin, so there isn’t much opportunity to provide insulation value,” says Wagner. “Much current work on this problem focuses on different methods of capturing solar energy, storing it and releasing it when temperatures are lower.”
Another approach has been taken by Birdair Inc., which is offering a material called Tensotherm™. This material is a sandwich, consisting of an external skin of PTFE/fiberglass, a middle layer of Lumira Aerogel material, and an inner layer of either PTFE/fiberglass or a vapor barrier material. This composite material promises to add insulation against heat loss and sound while providing high levels of translucency.
A further challenge is in designing openings in membrane structures. This isn’t so important for large roof projects, but for applications on the scale of even a multiunit dwelling, there must be robust, well-designed solutions for windows and doors.
Dr.-Ing. Walter Haase, of the Institut fÃ¼r Leichtbau Entwerfen und Konstruieren (Institute for Lightweight Structures and Conceptual Design), or ILEK, at the University of Stuttgart, Germany, is one of the people working at the forefront of research in these types of applications and problems.
“It is worth remembering that the initial design problem behind the development of current membrane architecture was the development of wide span roofs,” says Haase. “Frei Otto and his colleagues were principally concerned with creating lightweight solutions to enclose large spaces, but now energy consciousness and other design problems have entered the picture.”
New materials, new designs
A few of the ILEK’s recent projects in adaptive architecture are particularly notable. The first is an experimental application of Aerosil® (nanoporous high insulating pSiO2) and Phase Change Materials (PCM).
“Our prototype, ‘paul,’ [by Markus Holzbach] was built to demonstrate a few effects. The first is the potential insulating value that can be gained by using Aerosil materials in a multilayered fabric façade. We found the addition of just a few millimeters of Aerosil to be the equivalent of 10cm of concrete,” explains Haase. “The second was to investigate values of translucency, which we found to be dependent on the thickness of the PCM materials and temperature (since PCMs change between liquid and solid phases).”
Another interesting set of projects from ILEK addressed the issue of openings in fabric structures. The first is the “Adaptive Multilayered Textile Building Envelopes” project (funded by The Federal Institute for Research on Building, Urban Affairs and Spatial Development, Germany), an example of which appeared at the 2010 Deubau Trade Fair in Essen, Germany. This project demonstrated a series of ideas for ventilation and window openings in membrane structures, using different coated elastic fabrics. The opening shapes include a 3-D iris (“Twister” by Elias Knubben), a membrane-clad kinematic frame (“Flow” by Torsten Klaus), and eyelike openings that are powered by pneumatic actuators (“Open Up” by Tomas Kratochvila).
The twister concept is being developed further. “In order for ideas like this to be accepted in the building trades, we have to develop the ideas and materials further,” says Haase, “to show energy efficiency and durability. It won’t be possible to convince anyone to adopt these solutions if the membranes need to be replaced every five years.”
“It’s quite difficult to create an elastic material for outdoor applications,” says Wagner. “None of the presently-available materials work well against snow and wind loads—you would have to add some sort of underlying supports for these conditions.”
“There are two key materials you can consider if you want to build a dynamic membrane structure without mechanical framing elements: PTFE or PVC-coated polyesters,” says Cremers. “These materials can have 20 years of performance, like other construction-grade materials. And even these materials must be designed and used properly. And this includes the processes of fabrication, transport and installation.”
In summary, one of the biggest challenges in designing dynamic structures is the availability of materials. As creative solutions emerge, so will the technology and materials: The development of lightweight, wide span roofs. Before many of the visionary works that have been created for smaller buildings can be realized, issues such as acoustics, transparency, energy efficiency and elasticity must be resolved to the satisfaction of authorities issuing construction approvals and customers considering the total cost of ownership of a structure.