The site is in a region where earthquakes result from inner-plate shifting, similar to the trigger of the recent magnitude-5.8 quake in Virginia, rather than fault-line movement. Though numerous small quakes occur annually and rarely measure above magnitude 3, the building had to be engineered to resist quakes and hurricane-force winds.
The poor soil was also a concern for the foundation design. As a consequence, the steel frame is founded on 5-ft-dia caissons under 158 columns.
Designing a structure to meet all of those demands and also to be economical was “very challenging,” says Curtin.
Eleven roof trusses, 14- to 27-ft-deep, have a 464-ft clear span and a total span length of 614 ft. The trusses support numerous plane-assembly cranes, each weighing more than 50 tons. Each truss is comprised of two 307-ft-long sections. Each truss half weighs 221 tons, and each assembled truss contains an estimated 10,000 bolts, according to Boeing.
The building contains 18,000 tons of structural steel, including columns measuring 86 ft to the bottom of the trusses and 114 ft to the peak of the roof.
Anderson says there are “some pretty stringent tolerances for deflection of the steel” under load from the cranes. The deflection limits were designed into the frame.
“The seismic [requirements affect] the trusses and the sway range on the roof level,” adds Curtin. “There's a lot of cross-bracing.”
The biggest design challenge was achieving the necessary loading capacity for the plant's interior crane system while keeping the building's height under the limits imposed because the building is in the airport's flight path.
“The difficulty was not just in spanning the required [464-ft] clear dimension,” says Charles Wall, vice president of the structural fabrication division for the steel contractor CMC South Carolina Steel, Taylors, S.C., which also engineered the frame. The challenge was creating the required clear span with limited structure depth that could support heavy crane loads while still providing both the interior clear height to meet Boeing's needs and keeping deflection within limits, says Wall.
“Our truss design was the key to keeping the building envelope within the height restrictions,” he adds.
When they got up to speed, crews from Buckner Crane and Rigging, Buckner, N.C., received, assembled and erected one complete truss about every 10-12 days, Anderson says. Work would begin at dawn and usually finish by early afternoon. Design and fabrication took four months; steel erection took six months.
The team received a partial certificate of occupancy in the spring. Punch-list work continues. So does the installation of a rooftop solar photovoltaic (PV) power-generating system.
Sustainability, Solar
The team is likely to beat Boeing's initial goal of a LEED-Silver rating from the U.S. Green Building Council's Leadership in Energy and Environmental Design green-building rating system.
