The towering, hour-glass shaped sculpture in the Effnerplatz, Munich, Germany, is called Mae West, although it has a far more dramatic waist than the voluptuous 1930’s comedienne it is named after. The original Mae was, perhaps, a bit hefty by today’s swimsuit-model standard, but her somewhat abstract namesake sculpture need not worry about weight: constructed of carbon-fiber reinforced polymer, she’s probably the lightest 52m/170-ft tall sex symbol in Europe.
Mae West is made of carbon-fiber tubes that are wet-wound using an innovative, mandrel-less process. “Wet-wound” means that the carbon fiber is wetted with liquid resin during the winding process, and then cured to “freeze” the shape. If fact, it is because of the specialized technological capability of a German fabricator that the sculpture is structurally feasible. Carbon Grosssbauteile GmbH (CGB, Wallerstein, Germany) has the ability to make carbon composite pipes up to 42m/137.8 ft in length and 800 mm/31.5 inches in diameter. (A very detailed technical article explains the process in Composites World magazine. It is only summarized here.)
The artist who conceived the work, Rita McBride, formerly from New York and now a professor of sculpture at the Düsseldorf (Germany) Academy of Arts, was one of eight artists invited in 2002 to submit proposals for an Effnerplatz sculpture. McBride’s winning entry was conceived as a carbon-fiber work from the beginning, inspired by the recent examples of the material being used in bike design. She originally imagined telescoping carbon tubes. The ability of CGB to produce single long tubes made the telescoping idea unnecessary.
A single 40m/131-ft-long composite pipe for the sculpture weighs 1,102 lbs. In steel, it would weigh 6,614 lbs., more than six times as much. This huge strength-to-mass advantage is one of the hallmarks of composite construction.
In this project, both fiber and resin were customized to the load requirements of the sculpture. Fiber orientation and winding pattern were also engineered to this specific project. Pipe dimensions and winding patterns were designed using CADWIND software from Material SA (Brussels, Belgium), along with a computer design program that is proprietary to CGB. They calculated the finite element model (FEM) mesh, or fiber architecture, using ESAcomp 4.1 structural analysis and design software for composites materials from Componeering (Helsinki, Finland). The final pipe design features 20 plies of longitudinal, circumferential and low-angle helical fibers.
The City of Munich raised concerns about the safety of the sculpture, probably the tallest carbon fiber structure ever built. A system of carbon-wrapped steel pipe was developed for the lowest level of the sculpture. While the design suggested that it could have been built exclusively from carbon composite, the steel gives an extra measure of safety, including crash-worthiness (since it sits in the midst of traffic).
The winding method is an ingenious, mandrel-less process. The winding machine has a steel cylinder at each end of the pipe-length, with pins sticking out radially from the cylinder. The machine winds resin-wetted filament around a pin, carries it to the other end of the pipe-length and around another pin and back again. When all the longitudinal threads have been strung, they define a pipe. A curing hood is lowered over it to make the shape permanent. Then the stiffened filaments serve as a mandrel for further winding in other orientations. It’s almost like building a bridge: if you can string one cable from point A to point B, you can string many. Enough cables define a bridge, and then the structure can be filled in and beefed up.
The aesthetic “meaning” of Mae West may vary depending on the beholder. Its shape is said to relate to the round shapes of the Effnerplatz and the movement of traffic on the Mittlerer Ring road that encircles the inner city district. Its significance in terms of material science and structural engineering may be more profound. It is to composites, perhaps, a bit of what the Eiffel Tower was to iron construction in its day: a highly visible and engaging proof of concept.
images via Composites World