How a German engineering/architecture firm is leading the way in designing exciting and unusual fabric structures
By Mark Zeh
Recently I had the pleasure of talking to Gerd Schmid and Bernd Stimpfle, the managing directors of form TL. form TL is a structural engineering consultancy located in Radolfzell in the south of Germany on the west end of Lake Constance. The firm is composed of 11 structural engineers, one architect (Schmid), a draftsman and an office manager. Its portfolio is focused on the realization of imaginative forms and leading-edge applications for membrane and film structures.
Mark Zeh: The area around Lake Constance seems to be a hotbed of companies involved in membrane and tension architecture. Tell us a bit about the background of form TL.
Gerd Schmid: For me, it began when I was finishing my involvement with the firm SIB Stromeyer Ingenieurbau in Konstanz. I had been working with them for about two years on a project funded by the German government, to look into applications of lightweight structures, and two further years as assistant to Friedemann Kugel. This had been a fantastic learning experience, but their business focus began to shift away from membrane structures when Roeder bought them.
In 1994, I met Harald Muehlberger, the principal at IPL, a structural engineering consultancy in Radolfzell that was focused on membrane engineering. We began doing some business development work together and this quickly turned into a position for me in his business. First I worked with him as a project manager, then became managing director there in 1999. In 2000, I recruited Bernd Stimpfle, a colleague from Birdair Europe Stromeyer, to work with us.
Bernd Stimpfle: After my studies at the University in Stuttgart, I’d worked as an engineer at IPL. I’d left to join Birdair Europe Stromeyer in 1999, but then re-joined IPL as a managing director in 2000.
IPL was a family-owned company, so when Mr. Muehlberger passed away, we assumed leadership of the company. In 2004, 10 former employees of IPL founded form TL. Our focus is on membrane and film structures, with steel frames and cable supports.
MZ: Mr. Schmid, I noticed that you’re the only architect on the staff. How is your role defined?
Schmid: I also followed courses in structural engineering at the University in Stuttgart, but I decided to focus on structural architecture as my area of work. My role is important at form TL, since most architects don’t know yet how to work with membranes and tension structures. There isn’t a long history of reference design and there aren’t that many places where you can work to gain experience with this as you’re learning to be an architect.
Understanding the relationships of materials performance, spans, detailing and so on requires a lot of experience, so we provide that knowledge and experience to our clients during the design and construction phases of their projects.
MZ: What do you consider the most-challenging project that form TL has done?
Stimpfle: That’s hard. For me, it’s the Nouvelle DestiNation Expo .02 that took place in Biel, Switzerland, in May 2002. This was to be a “living exhibit” demonstrating the dynamic, vital relationship between the people and the state of Switzerland. We created this with the firm e2a Architekten. There were several aspects of the structure that interacted with people as they moved through its interior and displays. The entire structure was dynamic: the roof inverted three times per hour!
Schmid: For me, three projects really stand out for their technical challenges and also for our interactive role coming to a good aesthetic solution with the architects and builders.
The first is the GEK-Balance Road Show in 2003, with the architects Schienbein + Pier. It was an inflated system of bubbles and tubes that could be configured any way you would like. It was made from very thin, light fabric. It ended up being used for two years, though it was intended for six months of use, so there was a need for the occasional little repair, as pieces were torn and things wore out.
The second project is the Zénith de Strasbourg of 2008, with the architect Massimiliano Fuksas. It was the second use of a silicon glass fabric in an orange color. Mr. Fuksas had predefined the materials and span, so there was a lot of collaboration and interaction as we helped realize his vision. We had to negotiate lots of changes in radii and find ways to support the structure with inserted cables to make the structure feasible. We accompanied this project all the way to completion, consulting with Fuksas and supporting the general contractor and membrane supplier.
The third is the Modern Teahouse for the Museum fuer Angewandte Kunst Frankfurt (Museum for Applied Arts) of 2007, with Kengo Kuma. Mr. Kuma wanted to create a transitory structure to drink tea in. This project is the one where we invented the “soft shell” structure, allowing construction of these types of organic forms with pressurized envelopes. This involved further developing the theoretical base so that our calculations were close to reality. The structure is basically built up as the fusion of hundreds of bubbles. We used Gore™ Tenara® for this, for its light weight, translucency, foldability and especially for its nonsmelling properties. We were quite surprised that the final shape could withstand wind loads of 100Km/hour, with an inflation pressure of 1500 Pa. This was a relatively challenging project since one of the requirements was that it could be set up, used and taken down in one day. The teahouse is used in a public park in Frankfurt so the owners didn’t want to risk having it damaged by graffiti or vandalism. The structure can be deflated in about 10 minutes and the complete demount time is about two hours.
MZ: A lot of people are talking about the sustainable aspects of membrane structures. This is complex to understand, since the membrane materials often have only 10- or 20-year guarantees and are often manufactured from substances that are not considered particularly sustainable.
Stimpfle: There is a very positive aspect of these structures: there’s just so much less mass and material to the structures and all buildings require some sort of regular maintenance. With these structures, the membrane is usually replaced as the coating comes off of it, while the primary structure remains in place.
In the past, we mainly used PVC-coated polyester fabrics, which required a UV-protection coating. There isn’t a very good sustainability story with PVC, since it isn’t entirely recyclable and its production has some known environmental problems. It also tends to look dirty faster than the newer materials, since PVC has a relatively high surface energy.
The newer materials, such as PTFE coated glass, ETFE film and silicon-coated glass have much more attractive properties. They last longer, can be more translucent and are more self-cleaning. This also comes with a price.
Schmid: You can consider the fact that we can often do membrane spans with a mass per surface area of 5–15Kg/M2. Sometimes they’re up to 150 Kg/M2 if the membrane is not used as structure, but that’s an exception. This is quite a bit less material than is used in the construction of “rigid” buildings made from traditional materials.
Cost usually means that when ETFE is compared to glass, it ends up being the material of choice — an ETFE and steel structure can be about half the cost of a steel and glass structure.
There’s also been a change in the way companies are planning building projects. They’re thinking in terms of shorter cycles and reductions in their total investment. This makes membrane or film structures very desirable.
MZ: Looking at your portfolio, it’s possible to see a progression in materials technology and engineering understanding. What future developments do you anticipate?
Stimpfle: Our ability to calculate complex wind loads and computationally model the behavior of our structures will continue to improve. I also believe that our ability to create complex patterns will continue to improve. There will also continue to be improvements in detailing, resolving the problems where the hard and soft materials touch.
Schmid: I believe that silicon-coated glass will soon become very common in the language of architecture. We really have only about 50 years of development in membranes and films. Now we’re accumulating a “history” to draw from and a broadening acceptance of them. The positive experience from the Allianz Arena, as a structure, was a major step in conquering “the fear of relying on mechanical elements” that had accompanied structures using ETFE cushions. Now they’re becoming almost common.