One WTC Pedestal to Feature Triple-Laminated Glass from Interpane
December 14, 2011

By Sahely Mukerji,

The newly designed exterior cladding system of One World Trade Center that will cover the 185-foot tall secure base will be triple laminated, says Kenneth A. Lewis, project manager and director of Skidmore, Owings & Merrill (SOM) LLP in New York, the architect on the project. "It's low-iron glass with acid-etched finish on the #6 surface," he says. "The total area of laminated glass fins is approximately 106,000 square feet, all triple layer, so, the total glass used is about three times [that], about 318,000 square feet." Interpane Glas of Germany manufactured the glass, which features its Ipasol Bright White coating on #2 and #3 surfaces.

"The nature of the new design of the pedestal is to maintain in David Child's intention," Lewis says. Childs designed the original prismatic glass base of the tower. "We wanted to make it reflecting and refracting, in a luminescent kind of way, with an active surface, depending on the angle you're looking at," Lewis says. "The 13-foot 3-inch fins open and close, and are nominally 24 inches in depth. The fins are all fixed, but depending on where the viewer sees the wall the surface appearance changes. From the corners they are flat, but they open up toward the center, from flat to 60 degrees. Near the bottom the glass is flat, but as it goes up, it also opens up and then closes as it meets the tower shaft creating continuity between the two surfaces."

Behind the glass is a series of horizontal stainless steel slats that are offset from each other, and behind that are perforated metal panels to allow the wall to ventilate the mechanical systems located on the lower levels of the building. The stainless steel wall has hidden LED lights to give it a luminous glow at night, Lewis says. The wall has a stone base that creates continuity between the plaza and the wall. "The steel behind the glass is meant to recall the steel that marks the edge at the eight faces of the tower," he says.

It took the design team of six architects working with construction manager Tishman Construction, specialty wall and curtainwall fabricator APG International in Glassboro, N.J., and the Port Authority of New York and New Jersey 3-4 months to design the new pedestal. Part of that time frame was to explore the prismatic glass of the original design, Lewis says.
"We were working with Benson [Industries] to help us go through sampling, panelizing the system and answering questions about the glass, but their role ended when they wanted to bid on the project," Lewis says. "Then we started working with APG." APG built the mockup and worked with SOM on engineering.

The fins were rigorously tested in desktop and in the shop, Lewis says. As part of the specification the fins will go through scaled aeroelastic modeling and wind tunnel testing to verify their dynamic behavior. Further testing of the whole system will be done by Permasteelisa, which is installing the glass on the base, and then on a full-scale mockup. The full-scale performance mockup will include a uniform load test and a dynamic load test on the glass fins. The glass will be independently tested, as will the whole panelized assembly, he says.

Representatives of Permateelista were unavailable for comment at press time.

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