The Stuttgart team follows in the footsteps of architect Frei Otto, the founding father of modern tensile structures. Though his work with fabric membranes began as early as the 1950s, it was the 1972 Olympic Stadium in Munich that brought Otto international acclaim. This project represented only a fuller expression, on a far grander scale, of his much-publicized West German Pavilion for Expo 67 in Montreal.
The now-87-year-old architect didn’t come to tensility through any particular enthusiasm for coliseums or exhibition halls. Rather, in a turn that has entered the realm of design legend, his interest was piqued by observing soap bubbles—highly efficient structures with large spans and minimal surface area and shell thickness. (A second story, somewhat less broadly circulated, involves his stint as de facto camp architect while detained as a prisoner of war in England during World War II.)
“Otto’s main contributions came during these phenomenal two decades between 1952 and 1972,” says architect and engineer Werner Sobek. During that interval, he says, “Otto did not have that much support from engineering. That changed after the Olympics.” In 1974, Sobek, then an aspiring structural engineer, came into Otto’s orbit when he began his studies at Stuttgart, where Otto had led a loose band of tensile enthusiasts under the auspices of his Institute for Lightweight Structures for a decade. Along with the ’72 stadium, the Stuttgart group was to yield a crop of designer-technicians, who, just as Sobek, went on to refine the means and math behind fabric-based structures. Jörg Schlaich, a junior colleague of Otto and fellow first-generation tensilist, traces the development of today’s fabric buildings from Stuttgart straight through the Munich project. “The development went from concrete shells via cable nets to membrane structures,” he says.
For Sobek, who succeeded both Otto and Schlaich at the university, the urgent work of post-Otto tensile engineers focused on fleshing out the technical details underlying their forebears’ more intuitive, “fingertip-feeling” approach. “It’s a question of how to transfer ideas into reality—how to turn the soap-bubble model into a 1,000-foot span—and do it so you would feel comfortable sleeping under it,” he says. The contributions of engineers such as Horst Berger—who co-founded Geiger Berger Associates (now defunct) with David Geiger in 1968—have made projects such as the Denver International Airport come close to realizing the dream of tensility in mainstream building design. Nonetheless, even Sobek recognizes that working in textiles does impose certain constraints: “It really is mainly used for … cases where a building’s physical aspect means that thermal and acoustic insulation are not relevant.”
The fact that PTFE-fabric envelopes have such little insulating capacity means that they are commonly used as outdoor features where the program calls for only the merest roof over end-users’ heads. Toll plazas and train stations are often venues for modest installations of fabric. “In our portfolio, we’ve done a lot of canopies,” says David Campbell, president of Suffern, N.Y.–based Geiger Engineers, which he co-founded with Geiger and Paul Gossen in 1988.
Today, cost has limited the role that high-quality tensile fabric plays in architecture. “It really comes down to economies of scale,” says Peter Katcha, North American director of sales for Swiss fabrics manufacturer SEFAR Architecture. Sheathing a vast building volume in 500,000 square feet of his company’s proprietary fabric of woven PTFE fibers may cost millions of dollars, but it will typically cost much less per square foot than covering a smaller project. In other words, you might think twice about erecting a tensile structure over your suburban split-level.
The economic advantages of buying in bulk thus joins the list of reasons why tensile fabric roofs are prevalent in stadiums. Making the most of those factors was the objective of Jörg Schlaich’s firm, Schlaich Bergermann and Partner, and Geiger Engineers when they recently worked together on a project first designed by Geiger Berger in 1983: BC Place, a 54,000-seat stadium in Vancouver, British Columbia, Canada, which is home to the local football team. The building’s original, fixed-in-place tensile fabric covering had served its purpose for nearly 30 years, but the team thought that it didn’t take full advantage of new opportunities afforded to sports venues with the increased ductility of contemporary tensile fabrics.
To make the central portion of the new membrane roof retractable, the team turned to the fabric makers at SEFAR, selecting one of the company’s most ductile and translucent products. “They wanted the stadium to work in all weather conditions, and to be one that was openable to the sky above,” Katcha says. As a result, when it reopened last fall, BC Place boasted a nominally 100-meter-by-85-meter retractable tensile roof—the largest in the world. By simply drawing back the PTFE roof cover, the stadium may be used without costly building conditioning during warm months, making it a year-round venue.
But the tensile roof also provides something more. “It opens in about 12 minutes,” Katcha says. “Just think about the reaction of people watching that happen.” The structure, in effect, becomes a part of the entertainment.