Sculptors turn to FRP

Inverted Collar and Tie This article appeared in the Composites Design & Application, May/June 1997

Sculptors turn to FRP as an alternative to metals

- By Karen Lindsay

In 1993 artists Coosje van Bruggen and Claes Oldenburg received a commission from Deutsche Genossenschaftsbank Bank (DG Bank) to provide a sculpture, called Inverted Collar and Tie, which would sit at the entrance of the bank's new headquarters in Frankfurt, Germany.

Problem-Solution-Result In interviews published in a book about the project (Inverted Collar and Tie, by DG Bank and Cantz Verlag, Ostfilden, Germany), the artists discussed how they came to the decision to use glass-fiber-reinforced composites. Inverted Collar and Tie is their first non-metallic work.

The sculpture was to be a free-form necktie, seemingly blowing in the wind and anchored only by its upside-down shirt collar, which would sit balanced on the edge of a granite pedestal. Van Bruggen and Oldenburg traditionally use steel and/or aluminum to fabricate their large-scale sculptures, working with a fabrication consultant.

They say this project presented many challenges. It was the first time they had tried to do a large-scale version of a "soft sculpture," which typically only works in small scale. Another challenge was meeting some strict structural requirements. As is shown in the accompanying photo, the collar is actually cantilevered off the edge of the pedestal. Working with their fabrication consultant, Don Lippencott, they first tried building a steel frame, that would then be draped with canvas. Unfortunately, the thickness of the canvas required to achieve the "soft" fabric-like look of the sculpture once enlarged, did not have the desired drapability.

The second plan involved using sandcast aluminum panels, which would be welded together to achieve the shape, and a structural stainless steel armature for internal support. To sand-cast the panels, a polyurethane foam pattern of the full-size structure was needed.

Lippencott contacted a firm called Cyberware, which manufactures 3-D digitizing equipment that can faithfully enlarge any item. In turn, Cyberware recommended William Kreysler & Associates (K&A), a Petaluma, CA-based molder and fabricator that uses Cyberware equipment, along with its own extra-large CNC milling machine, to build large parts.

"We've combined several technologies to allow us to build large-scale models," says K&A's president, Bill Kreysler. The technology involves the use of a Cyberware 3-D Digitizer, which is basically a laser beam connected to a video camera and computer. The laser measures the surface of a model to produce a 3D image in the computer. From that, a tool path can be generated for CNC milling.

Composites instead of aluminum
In discussions with Lippencott about creating the large-scale polyurethane foam pattern for the sand-cast aluminum shapes, Kreysler identified a problem. "The slender vertical section of the tie would complicate the design of the internal armature," he says. "I saw an opportunity to use composites, instead of aluminum, and suggested that an all-composite sculpture might solve some of the problems already identified with the project."

And while the artists were initially hesitant about using composites, because of what they called its "kitschy-ness," they also saw a solution. The use of glass fibers would create the "soft" fabric-like quality needed to achieve drapability.

"I knew that once we manufactured the foam pattern, we could use finite element analysis to engineer an exterior skin from composites that would serve as both the shape of the sculpture and as its structural support," Kreysler says. The cavity would then house a hand-laminated, oriented fiber composite box beam.

Inverted Collar and Tie Preliminary engineering studies conducted by K&A and consultants Juri Komendant and Kurt Jordan showed that the concept of using the exterior shape as the structure was workable. "Because the initial results of the studies were promising, the artists authorized us to begin the foam enlargement process," Kreysler says. Several digital scans of a 40-in. model were created using the Cyberware 3-D Digitizer and from those, a tool path was created for the CNC milling machines. The machines carved the full-scale polyurethane foam core of the Tie sculpture. This core then served as a male mold for the outer skin, which was composed of isophthalic polyester from Cargill, and oriented strand fiber fabric from Knytex. In some areas, such as the extreme tip of the Tie, a mirror image of the top and bottom surfaces were milled to create a matched female mold because the section was very thin (4-5 in.) and a foamed male mold would have been too fragile.

After partial completion, the composite skin was cut and the foam excavated to form the box beam cavity. Additional laminate was placed inside. After reassembly and faring, a light layer of chopped glass and isophthalic polyester was applied to bury the fairing and to provide the desired texture. A 20-mm. thick layer of NPG gelcoat (from Lily Ram), and a final coat of Rohm & Haas Acryloid B-72 clear acrylic was applied. B-72 was selected for its resistance to weathering and UV rays, while being removable with denatured alcohol (a beneficial characteristic when surface stain such as graffiti or soot is likely).

Kreysler says only one problem turned up in the studies. "Because of the 'knot' of the tie was designed to be cantilevered over the edge of the granite pedestal, it appeared that FRP alone could not provide the stiffness required to support the sculpture under the German building-code-mandated loads as efficiently as a higher modulus structural material," he says. "We considered using a carbon/epoxy system but rejected it due to cost." But because weight was not an issue, Kreysler says a solution was found with a 12-in.-dia., 1/2-in. wall steel pipe, which was bent and buried in a casting of polymer concrete. The pipe stops approximately 3 ft. above the knot and provides the necessary stiffness.

Inverted Collar and Tie The finished sculpture was shipped in May 1994 via barge from Kreysler's facility on the Petaluma River to the Oakland shipping terminal on San Francisco Bay. It traveled under the Golden Gate Bridge, overseas through the Panama Canal, and on to Rotterdam. It reached its final location in Frankfurt, via the Frankfurt-Westhafen river port-some 8,000 miles from its place of fabrication.

Since the completion of Inverted Collar & Tie, van Bruggen and Oldenburg have turned to composites (and K&A) for two large-scale projects: The Houseball, to be located near the Berlin Wall at Checkpoint Charlie, and Saw, Sawing, which was installed at the Tokyo Convention Center in 1996. Others are planned.

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Last updated: 09/21/06