By Mark Zeh
It’s been more than five years since the opening of the Allianz Arena in Munich, Germany. In the meantime, the stadium—designed by Herzog & de Meuron Architekten of Basel, Switzerland—has become a symbol of both Munich and Germany. Construction of the Allianz Arena, located in Fröttmaning, along the autobahn between Munich and the Franz Josef Strauss Airport, was completed on April 30, 2005. The opening game in the Allianz Arena, between TSV 1860 (Munich’s second division team) and FC Nuremberg was played on May 30, 2005.
The external façade of the arena, with its 2,760 diamond-shaped cushions made of 0.2mm thick ETFE foil, makes a memorable first impression, particularly when lighted at night in one of the team colors (red for FC Bayern, blue for TSV 1860, or white for the German National Team).
Recently, I had a chance to talk to a few of the key players in this success story and get them to revisit the project and talk about lessons learned.
“The proposal of Herzog & de Meuron Architekten, with its striking lighting concept, was immediately selected,” says Peter Kerspe, CEO of Allianz Arena Muenchen Stadion GmbH. “The stadium is purpose-built for soccer and is not allowed by the city of Munich to promote concert events or other arena-type shows. We do host a large variety of smaller events and had a full house for public viewing of the European Champions League Final. There were some setbacks along the way, but the stadium is a big success.”
Color and light
“The initial concept emerged from the competing users of the stadium,” stated Tim Hupe, now managing director of Tim Hupe Architekten, who worked on the project in his former role as the lead project architect for Herzog & de Meuron. “The question was really how the structure could be transformed into the individual identity for the two home teams. Changing colors through lighting was the only clear answer.”
Richard Fuchs, managing director of R+R Fuchs Ingenieurbüro für Fassadentechnik GmbH, the structural engineering firm responsible for the façade, explained, “This was the first really large pressurized-cushion ETFE structure built. There were some design problems to resolve because of its scale, but it’s really a multiplication of design elements that were already proven. When we first saw Herzog & de Meuron’s design proposal, they wanted to use polycarbonate panels, but we recommended the use of pressurized ETFE cushions, due to the fact that this material won’t burn without a supporting heat source. Its transparency also allowed us to fulfill the lighting element of their design proposal.”
“From a design perspective, it was fortunate that we were able to change from the initial concept of polycarbonate panels to the ETFE cushions,” adds Hupe “We were able to increase the size of the diamond-shaped elements to more closely match the architectural scale of the structure.”
Bernd Stimpfle, one of the managing directors of form TL Ingenieure für tragwerk und leichtbau GmbH, worked on this project during his time at IPL, one of the structural engineering firms that supported R+R Fuchs. He explained, “The structure is like a curtain hanging from a hoop that you can see running around the structure, one row of cushions above the Allianz Arena sign. The roof is like a hat floating on top of this hoop. The structures that support the façade are connected to the main stadium structure by flexible elements that take up differences in thermal expansion.”
“The façade of the stadium has been particularly trouble-free,” says Kerspe. “The outside washes clean from rain and we only need to clean the interior surfaces occasionally.”
Working with ETFE
Hans-Juergen Koch, of Koch Membranen GmbH, supplier of the ETFE film for the project, says “ETFE has low surface energy, so things don’t stick to it. Since the outer façade is completely open to the environment on both sides, we didn’t need to worry about condensation. The amount of airflow through the cushions takes care of the small amount of condensation that may normally occur.”
As I toured the stadium and looked the site over, I found the ETFE cushions to be remarkably clean and the general structure to be in good shape. There are some repairs to the concrete at the top level of the stadium, likely a result of settling and expansion. One feature of the membrane façade that will probably be the first to require maintenance is the movable sunshades.
“With the benefit of hindsight,” says Hupe, “I’d simply leave the moveable shade elements out and change the color selection of the roof elements. ETFE is transparent to UV light, so shading that is visible to humans doesn’t affect the growth of the grass on the field. The moveable shades are a complex solution, but now the choice of materials available for this application is also greater.”
The simplicity of the lighting inside the external façade is impressive. Each cushion is lighted by two fluorescent lamps above it and two below, for a total of 25,344 fluorescent tubes in the façade lighting plan.
“It required quite a lot of experimentation to get the lighting right,” states Hupe. “It was important that it looked uniform from the outside, but also wasn’t noticeable from inside the stadium. It’s possible to see the Munich skyline at night from inside the stadium while the lights are on.”
Creating a landmark
“It was particularly challenging to create the even light that Herzog & de Meuron was showing in their concept. At first, we thought about using RGB LED technology,” says Karl Fritz Roll, project leader for Siteco Lighting GmbH, “but even if we were given this project today, I’d still recommend the fluorescent tube solution that we found. We determined that it would be much simpler and more cost-effective to create a special filter for each light fixture, with six tubes in each fixture and red, blue and white filters running over each pair of tubes. Color is changed by simply switching on the tubes that are under a particular filter color, so when the lights are on there are only two tubes on in any given fixture. Per watt-hour, fluorescent is very inexpensive and the reliability is very high. Due to the placement of light fixtures and scale of the structure, it can be quite expensive to perform any maintenance.”
It may seem that Allianz Arena is missing a big opportunity by not using LED technology and using its large façade as a display surface. “Since the arena is right next to a major thoroughfare, the city said we could not use the surfaces in this way because it could be distracting to drivers and lead to accidents” says Kerspe. “When we first switched on the lights and switched between the colors to test out the system, it led to some major traffic backups on the autobahn!”
During my visit to the arena, I noticed quite a few discarded cigarette butts in the supporting structure for the ETFE cushions. The façade is technically “outside” of the stadium, so smoking is allowed between the stadium building and the façade. I wondered whether it would be possible that a still-smoldering cigarette could possibly melt a hole in the film. “I don’t think so,” says Stimpfle. “The material certainly won’t burn from such a small heat source. It also seems unlikely that a cigarette would do more than create a local darkened area.”
“We were more concerned about effects of vandalism,” says Hupe. “We needed to be sure that if some angry fan punctured a cushion, it wouldn’t have a disastrous effect on the structure.”
The value of hindsight
As to how things look with the benefit of hindsight, the parties involved with the project provided a few key insights.
“We were required to build quite a large parking garage,” says Kerspe. “It’s the largest in Europe and is 80 to 90 percent full for each game. That can mean that it takes a while to empty after games. It would be nice to have the chance to rethink this.”
“If it were possible, I’d try to integrate the façade design into the overall structural design much earlier,” says Stimpfle. “One of the design challenges in creating the façade was creating features to allow for the differing amounts of thermal expansion between the various materials.”
“One of the main challenges in undertaking a membrane structure project of this scale is identifying a company that can carry out the project,” adds Fuchs. “Most of the companies are small engineering offices that work with companies that install the membranes. My wish would be for a larger number of companies that integrate all of the structural engineering functions, including steel, concrete and membrane technology.”
Hupe notes, “It’s already hard to imagine from the standpoint of our present technology, but it was really difficult to even sketch how the stadium would look. I’m not sure how I could have done this differently, but it’s important to keep in mind how development of technology has been accelerated through projects like this.”