Into the Wild Blue
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THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS |
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ONE OF THE LARGEST structural applications of stainless steel, the Air Force Memorial in Washington,
D.C., consists of three spires, 64 metres high. |
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EACH SPIRE HAS A SKIN of stainless steel plate (S31600)that is 19 millimetres thick. |
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Stainless steel sours to new heights in U.S. Air Force memorial by Virginia
Heffernan
Nickel Magazine, December 2006 -- The Air Force Memorial recently unveiled in Washington, D.C. ranks as one of the world’s largest structural applications of stainless steel, along with the Dublin Spire in Ireland and America’s largest memorial, the Gateway Arch.
Consisting of three stainless steel spires reaching 64 metres into the air, the new memorial honours the millions of men and women who have contributed to the United States Air Force and its predecessors over the years, including 54,000 who died in combat.
Each spire has a 19-millimetre-thick skin of low sulphur (0.005% max) S31600 stainless steel covering a core of reinforced concrete. The total weight of the spires is 7,200 tonnes, including 345 tonnes of S31600 plate, containing 12% nickel.
Engineers involved in the design chose S31600 to prevent corrosion and allow the structure’s appearance to be retained over decades without the need for manual cleaning. Though Washington is not coastal, nor particularly polluted, the memorial is surrounded by three highways that use de-icing salt that could threaten a lesser material.
S31600 also provides structural integrity to help withstand the tendency for the spires, which are curved, to sway in windy conditions.
“From a structural standpoint, the Air Force Memorial was challenging,” says Catherine Houska, senior market development manager for TMR Stainless, the consulting firm chosen to provide advise on materials for the project. “When you have that kind of a curve unsupported, except at the base, it is going to tend to move even with the slightest breeze. There are elaborate damping systems to prevent it from shaking apart.”
The “ball-in-box” damping system contains thirteen 20-inch-diameter lead balls, weighing 2000 pounds each, encased in stainless steel shells. The balls roll freely within boxes that are lined with synthetic damper pads. As the balls hit the pads, energy is dissipated and structural movement constrained.
The memorial was designed by the late James Freed, the internationally-renowned architect from Pei Cobb Freed, while global engineering firm Ove Arup developed the spire structure. The spires are meant to evoke the bomb –burst flying formation made famous by the United States Air Force Thunderbirds.
Construction commenced at the beginning of 2005 and was completed in the autumn of 2006. The total cost for construction was more than US$30 million.
PHOTOS: Catherine Houska for Nickel Institute
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