Steven F. Udvar-Hazy Center Construction

Raising the Roof

General contractor Hensel Phelps Co., along with the subcontractor team, is "raising the roof" of the aviation hangar at the Steven F. Udvar-Hazy Center. The vaulted roof of the hangar is 103 feet high in the center, the hangar is 248 feet side to side-with no center supports!

The hangar is supported by arches or "trusses" of steel. In engineering terms, a "truss" is a rigid framework. With their curved shape, the trusses actually support both walls and roof of the giant hangar.

Hensel Phelps built 42 thrust blocks for the trusses, steel and concrete bases that support the great weight of the trusses on either side. (They are called "thrust blocks" because the weight on the trusses causes their ends to push out or "thrust.")

	The trusses are being fabricated in three sections, using steel from America. ADF International Inc., the structural steel subcontractor for the project, performs the initial fabrication in Montreal, Canada. The long tubular chords of steel and connecting purlins are then trucked to northern Virginia. Image courtesy of ADF International Inc.
	At the construction site, on customized jigs, iron workers finish the assemblies: two side sections and one center section for each truss. Photo by Mark Avino, NASM; ©2002, Smithsonian Institution
	Upon completion, the 58-foot side sections, each weighing approximately 35 tons, are taken by crane to the thrust blocks that will support them, starting on the far north end of the hangar. Photo by Mark Avino, NASM; ©2002, Smithsonian Institution
	Very carefully, a side truss section is positioned so that the "lower lip" rests on its thrust block. A "guide pin" is lined up with a center hole in the base. Here the sections will wait in a lowered position. Large bolts will hold the parts together when raised. Photo by Mark Avino, NASM; ©2002, Smithsonian Institution
	ADF joins four side sections into a "block," one block on the east and one on the west. Galvanized acoustical decking is welded and screwed into place, lining the trusses with the inner most layer of the ceiling-roofing sandwich. Photo by Smithsonian staff; ©2002, Smithsonian Institution
	A block of side sections is ready to be lifted into place. Photo by Smithsonian staff; ©2002, Smithsonian Institution
	Late on the afternoon of January 28, 2002, ADF lifted the eastern block of side sections, using two cranes. The cranes' cables were connected to a strong-back, which distributed the significant weight between the two cranes. At each of four thrust blocks, curved guide pins slid into place (see photo above) as the sides slowly rose. Large bolts were fastened in place, securing the steel to its concrete bases. Four shoring towers added temporary support. The crew finished work on this unusually warm winter evening as the full moon was rising. Drawing courtesy of Hensel Phelps Construction Co. Photo by Mark Avino, NASM; ©2002, Smithsonian Institution
	On January 29, the same crews erected the western block of side trusses, and they did it in one hour. Photo by Mark Avino, NASM; ©2002, Smithsonian Institution
	To complete the arches, ADF is fabricating 228-foot center sections on a larger jig just south of the hangar construction area. As each 70-ton section is completed, it is walked by crane to a temporary resting place. Photo by Mark Avino, NASM; ©2002 Smithsonian Institution
	On January 30, at about 1:30 p.m., a single 188-foot crane--higher than an 18-story building--picked up the first center section and headed for the waiting side sections. Two men on each end of the truss walked along with the crane, grasping guide lines as the load was maneuvered down the hangar. Photo by Mark Avino, NASM; ©2002 Smithsonian Institution
	Painstakingly, the crane operator, under the direction of an ADF choreographer, aligned the center section with the northern most pair of side trusses. Two steel workers waited on both the east and west sides, perched atop the raised steel, equipped with the tools of their trade, ready to connect the giant steel members. Drawing courtesy of Hensel Phelps Construction Co.
	Also on each side was another ADF worker in a boom lift. At 2:35 p.m., the three men on the west side grasped the center section and began the hard job of fitting the steel into waiting slots and connecting the bolts. Photo by Tatiana Haagensen, HOK; ©2002 Smithsonian Institution
	Just after 3:00, the east-side team began their work. The first truss-number 68-was complete! Photo by Tatiana Haagensen, HOK; ©2002 Smithsonian Institution
	By mid-summer, the 984-foot-long hangar will be under roof and closed in. When the museum opens in December 2003, aircraft will hang from the trusses, and the arched roof will shelter this unique and historic collection.

View the Behind the Scenes article on the raising of the last aviation hangar truss.

Back to Udvar-Hazy Center Behind the Scenes Page