It looked good on paper: Use huge, golden-colored limestone rocks to make an overhang 130 feet above the entrance of the National Museum of the American Indian on the Mall. It would look like the overhang in a Southwest canyon. No ugly, concrete columns underneath: It would seem as though suspended in air.
Architects and engineers had designed it, but no one was exactly sure how well it would work. Making it work was up to Bethesda's Clark Construction Group LLC, the area's largest contractor with $2.7 billion in revenue last year.
Making the dramatic limestone overhang work above the National Museum of the American Indian was one of many challenges for Clark Construction Group.
(Bill O'Leary -- The Washington Post)
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Therein lies a tale of how one of the Mall's most unusual and ambitious buildings overcame several big structural obstacles behind the scenes to make its grand opening Sept. 21.
To make the limestone overhang work, for instance, Clark had to dig a hole 30 feet below street level; drive a tall steel beam into it; and reinforce the base of the beam with dirt and concrete. Then it had to make an arm of heavy-duty steel, the kind typically used for constructing bridges, that would extend 100 feet from the beam. The arm, made of V-shaped steel trusses and weighing 750 tons, would have large pieces of limestone hung on it to create the look of the canyon wall.
But Clark found the overhanging beam was too heavy. A dozen engineers, architects and designers spent four months going once a week to a Norfolk steel-maker and puzzling how to make the contraption hold the weight.
"It was like making a diving board that only King Kong could flex," said V. George Conard, a Clark vice president.
The overhang was one of the many challenges Clark said it faced in the almost four years it has worked on the 450,000-square-foot museum, which will house one of the most extensive collections of Native American artifacts in the world.
Building the roughly $200 million museum required 500 engineers, architects, carpenters, electricians, stone masons and other laborers. Some of the challenges: laying huge steel beams and slabs of concrete around underground supports and electric and water lines; carefully installing a huge steel dome in the ceiling; and building a structure that has few straight lines, requiring making walls of concrete curve. Speaking of concrete, it has enough to fill 250 swimming pools; enough limestone and granite to cover five football fields; and the steel in its basement -- if laid side-by-side -- would extend eight miles.
"This was like building a space shuttle versus building a go-cart," said William I. Magruder, senior vice president at Clark.
The 98-year-old company had built convention centers in Los Angeles, Chicago and the District; airport terminals in Baltimore and Orlando; sporting venues including Oriole Park at Camden Yards in Baltimore, MCI Center in downtown Washington and FedEx Field in Landover; plus hundreds of office buildings, including Discovery Communications Inc.'s new headquarters in Silver Spring.