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With military priorities setting the pace, the San Antonio office of SpawGlass is working at jet-engine speed to construct the C-5 Training Schoolhouse Complex at Lackland Air Force Base in San Antonio.
General Contractor SpawGlass is delivering the two-building, fast-track project while contending with security requirements and tight access to the on-base jobsite.
Photo by Rob Patterson. |
Ground was broken in June for the $16 million, two-building project that is slated for completion in September to accommodate the C-5 cargo aircraft training operation being transferred from Altus Air Force Base in Oklahoma.
To complete the two concrete-frame, brick-clad structures, general contractor SpawGlass has to contend with security requirements in the buildings, access to the on-base jobsite and a tight timeline under a best-value contract.
"If this were a Wal-Mart we'd just be throwing it up," said Larry Reser, quality assurance representative for the U.S. Army Corps of Engineers.
Structural specifications for the three-level, 69,000-sq.-ft. Ground Training Unit required that the frame for each floor be completed before the next one was started.
Because the structure is adjacent to an airport runway, 14-in. of tarmac totaling 2,200 cu. yds. had to be broken through and removed along with 3,500 cu. yds. of clay underneath.
The building sits on bell piers drilled 40 ft. into the clay to reach a less-expansive layer.
"The piers provide additional bearing capacity for the downward loads," said Gary Dupere, project manager with the San Antonio office of CH2M HILL architects. "They also provide uplift resistance for any expansive forces we get from the clay there."
Double-T concrete columns on the first level help support the load of two weapon systems trainers, a cockpit procedures flight simulator and other C-5 task simulators. A three-story bay at one end with an overhead gantry crane houses a cargo-load trainer and ramp and cargo-door trainer. By mid September, SpawGlass was 30 percent done with the building, finishing the foundation and first-level frame.
"The trainers are on their own separate foundations," Dupere said. "The loads are not exceptional--not any more than the three-story building columns. It's just that we had to provide isolated foundations for the trainers so they wouldn't have any kind of movement if something else moved."
The building is also designed for progressive structure collapse as a security measure against explosions as part of the Department of Defense's anti-terror provisions. "At any given point, if you lose 700 sq. ft. of the building, the remaining structure stays the same," said Al Vazquez, project executive for SpawGlass.
And Dupere added: "If they lost a column or a beam, the building is designed to spread the load to the adjacent columns or beams. The basic plan is to provide redundancy throughout the entire structural system."
The design requirements challenge the fast-track schedule. "You have to wait to get to the next level to put your hollow-core floors in and continue," Vazquez said. "So it's not fast construction though it has to be done as quickly as we can."
The roar of jet engines from flights and engine testing on the neighboring runway also had to be addressed. "We added an extra layer of insulation into the building systems and paid a lot of attention to the use of acoustical sealants," said CH2M HILL project architect James Deane. "And we used glass that would improve acoustical performance.
"Normally on a building like this where you'd have a concrete frame, a stud infill and a brick veneer, you'd see some sheeting on the exterior cavity and then your brick. We added an extra 2 in. of extruded polystyrene to help deal with the noise and the vibrations that come through."
An extra layer of insulation was also designed into the roof system. "The Ground Training Unit has an inverted roof membrane assembly: membrane on top of the deck, insulation on top of that and then pavers are used to hold that down," Deane said.
CH2M HILL designed the structures to accommodate future adaptations. "We do a lot of renovation work and studies at other bases," Deane added. "Time and time again what we see is purpose-built buildings, and 10 years later something happens and it's difficult to adapt the building. So while we were working on these, in the background we kept in mind that the buildings would be flexible and that the use could change."
For example, the trainers are situated in the bay area, and a removable architectural metal panel in a side wall allows trainers to be installed and removed.
"We tried to cluster them in a way that makes some sense and allows future equipment to be put into those spaces," Deane said.
Fast-tracking also required SpawGlass to build around a buried power line through the site before San Antonio's City Public Service could come in and finish connections to a new conduit.
"We had an underground electric line right down the center of the building," Reser said. "Some contractors would stop and wait for a change. SpawGlass worked around it. We exposed it, knew where it was, drilled our piers, did our excavation, drove our piers and built a rerouted line around the building."
Excavation is complete and piers are being drilled for the nearby two-story, 24,700-sq.-ft. Flight Training Unit classroom building. "There's three foundation piers at the FTU that we cannot drill yet because there's an existing 8-in. waterline that has to be relocated," Reser said.
The FTU building, which does not have the progressive collapse feature, features a pitched-metal roof supported by light-gauge trusses.
Due to the war in Iraq and terrorism concerns, all workers are screened for security. "Everybody who comes inside to work or visit has to have a permit or a badge," Vazquez said. "And we have to apply for it."
To avoid traffic at the working airbase, all of concrete pours totaling 5,800 cu. yds. are done between 3 a.m. and 7 a.m..
Antiterrorism measures also require that the buildings sit 80 ft. from any parking areas and have a 30-ft. perimeter that is clear of anything that might provide cover for an attacker.
Finishing the two buildings on time is essential to supporting the Air Force C-5 missions. "They're going to bring the first class in here in January 2007," Reser said.
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