Loads from the veil will come down onto a 32-ton, 57-ft-long girder at the base. The girder, called a touchdown beam, sits on Grand Avenue and is shaped like a Viking ship, says Joe Healy, MATT's vice president and project executive.
The bottom of the girder is embedded 5 ft below the sidewalk in a bathtub-shaped steel plate, measuring approximately 5 ft wide, 10 ft long and 5 ft deep. The girder is secured to the plate with 56 anchor bolts.
The touchdown beam can manage loads of up to 3,000 tons, and will rock on a central pivot point allowing the entire veil structure to see-saw slightly along its plane during an earthquake. Each end of the beam is allowed to move up and down by a maximum of ¾ in.
The veil is not simply a "cosmetic architectural curtain wall," says Nabih Youssef, principal with the local Nabih Youssef Structural Engineers, which worked with Leslie E. Robertson Associates, New York City, on the project's structure.
"The veil and the vault work in concert," Youssef says. "They are integral components of the intent of the design and of the complete structural safety of the building."
Outside the Box
The gallery's 200-ft-square clear-span roof cantilevers over the front of the museum and is supported by five 6-ft-deep plate girders, each 190 ft long and weighing roughly 70 tons. The roof has 318 skylights, all facing north to protect artwork from harmful direct sunlight.
Located in the center of the building, the concrete vault's sweeping, curved underside provides shape to the lobby below and its roof also is the floor of the third-level exhibit space. Its concrete slab floor cantilevers 45 ft over the lobby.
A tubular glass elevator and a 102-ft-long, tube-like escalator will transport visitors from the lobby through a second-floor storage vault and into the third-floor main gallery, which has 23-ft-high ceilings and 35,000 sq ft of column-free space. The lobby is surrounded by 37 glass panels, each measuring 20 ft x 5.5 ft and weighing 2,198 lb. The galleries feature 52 glass panels, each about 25 ft x 5 ft and weighing 4,881 lb.
To plan the construction of the curved lobby walls and ceiling, MATT first computer-modeled the space in 3D. Next came full-size paper templates for each individual metal stud. Crews would hand-bend each stud to match the template. Next, workers in the field preassembled 10-ft x 15-ft sections, before lifting them into place and attaching them to the concrete structure above.