Fabricator: TriPyramid Structures, Inc.A treasured national symbol, America’s original Star-Spangled Banner occupies a place of honor in the Smithsonian’s National Museum of American History in Washington, D.C. The flag was first raised on September 14, 1814, when U.S. soldiers at Fort McHenry celebrated a crucial victory over British forces during the war of 1812. The sight of those “broad stripes and bright stars” inspired composition of what would eventually become the U.S. national anthem.
In 2009, nearly 200 years later, the flag was installed in a permanent gallery at the museum. Abstract Flag, a stylized sculpture designed by Skidmore, Owing & Merrill, marks the gallery’s entrance. Formed of 15 ribbons covered with 960 ‘pixels’ of mirrored polycarbonate, the sculpture suggests the fluid motion of a flag waving in the breeze.
Lending structure to artistry
Designed by structural engineers Robert Silman Associates, the sculpture’s framework is a complex cantilevered arrangement of horizontal and vertical steel trusses formed of small diameter rods.
An uncommonly rigid structure was required to support more than 900 glistening polymer pixels mounted on the sculpture’s stainless steel surface. Fabricated by TriPyramid Structures, Inc., the sculpture’s stainless steel framework is anchored to the wall at only one spot. Spanning 38 by 19 feet, nearly all of the flag’s weight is supported on what appears to be its flagpole side. Four undulating arms splay out before tapering at their end points.
A strong and stable solution
For a framework both light and strong, the structural engineers selected Outokumpu’s lean duplex, Forta LDX 2101. The grade provided the high yield strength, welding stability and superior machining properties essential to the project.
The high yield strength of Forta LDX 2101 translated into reduced material need. The framework’s round bar, ground to a mirror finish, showcased the superior machining properties of the material. Welding stability was demonstrated through precise interconnections, where acceptable tolerances were limited to fractions of an inch. Through use of this advanced material, no point on the sculpture exceeds specified tolerances by more than 1/16th of an inch.