PENTAGON MEMORIAL [Stainless_Steel _Casting+CNCtech]

Project: Pentagon Memorial, Arlington, VA US

Architect/Designer: KBAS Studio

Featured material: Stainless Steel

The pentagon memorial required the collaboration of a network of disciplines from melting, pouring, and installation procedures to produce 184 of its commemorative benches. Designed by KBAS Studio, but put together by 28 different firms, the design proved to be a massive undertaking of flow of information and components for the design and fabrication of molds using computer numerical controlled technology (CNC). In this project, the encounter between digital technology and the archaic methods of shaping metal redefined the material’s properties, the involved disciplines, and the new parameters of work-flow from past to future practices.

At the Pentagon Memorial, each unit was constructed of a super duplex stainless steel alloy, designed to last more than 100 years, maintain its structural integrity, and be compatible with other materials and the reflecting pool that surrounds each bench unit. Duplex stainless steels, which generally contain equal amounts of ferrite and austenite, provide better resistance to pitting and crevice corrosion in most environments. They also have superior resistance to cracking due to chloride stress corrosion, and they are about twice as strong as the common austenitics. Therefore, duplex stainless steels are widely used in the chemical industry in refineries, gas-processing plants, pulp and paper plants, and sea water piping installations.

The memorial’s components called for innovative approaches. The benches alone required intensive engineering to reduce their weight to just under 1,000 pounds from an estimated 5,000 pounds. The foundry that made them invented new machines to ensure their integrity in casting and polishing. Stonecutters used digital technology to cut and polish the granite pieces used on the benches, and each piece required a final hand-polishing. Even unseen components of the memorial required thought: Ninety percent of the MEP scope was necessary, but couldn’t be visible; more than 25 miles of utility lines are buried under the memorial to deliver water and power. This underground complex of utility lines had to fit within the existing utilities, including permanent and temporary lines installed during the initial 9/11 cleanup. And, of course, the permanent lines had to remain operational throughout construction. The design-build team used state-of-the art technology including ground-penetrating radar to identify existing lines—some of which were not on any plans—and 4D modeling of the results to develop a bottom-up picture of them and position new lines.

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