On a Clear Day, You Can See for Miles and Miles...
SAN FRANCISCO INTERNATIONAL AIRPORT (SFO)
AIR TRAFFIC CONTROL TOWER & INTEGRATED BASE FACILITY
Location: San Francisco, CA
Client: San Francisco International Airport and Federal Aviation Administration (FAA)
Size: 231-ft tall tower; three-story, 50,000 sf OFB
Budget: $90 million
Services: Structural Engineering, Secure Design, Seismic Design
Construction: Hensel Phelps Builders
- 1st FAA ATCT to use design-build
- 1st FAA ATCT delivered with airport as the lead
- 1st FAA ATCT unobstructed, 270’ cab view
Imagine a 650-sf, glass-enclosed space housing 13 work stations equipped with highly sensitive instrumentation approximately 20 stories in the air. Now imagine the task before the 13 people manning those work stations. About 1,155 times a day, commercial airliners — each carrying an average of 107 passengers — will take off and land here on runways laid down over reclaimed marsh land, just four miles from the San Andreas Fault.
So what is this sky-high viewfinder? It’s the cab of the Air Traffic Control Tower (ATCT) at the seventh busiest airport in North America: San Francisco International Airport (SFO).
Beginning around 2000, the Federal Aviation Agency (FAA) warned that SFO’s control tower would not withstand another major quake. The old tower had to go. Walter P Moore teamed up with Fentress Architects and Hensel Phelps Builders to deliver the project on a design-build basis. The new tower, sandwiched between Terminals 1 and 2, would replace the one first built in the 1960s and remodeled in the 1980s—the one knocked out of commission during the 6.9-magnitude Loma Prieta earthquake in 1989.
Two factors primarily drove the engineering: first, seismic performance; second, unobstructed views for the air traffic controllers. The engineering, in turn, drove the architecture. The result is an iconic, torch-like 21st-century ATCT, engineered to remain operational in a Maximum Considered Earthquake. In San Francisco’s case, that’s a magnitude of 7.5. Furthermore, instead of the normal 30˚ unobstructed views found in most of today’s towers, SFO’s has a 270˚-wide view of air traffic.
The Self-Centering Factor
To achieve maximum stability, the structural system we chose for the tower is a cast-in-place, reinforced concrete core cylinder, wrapped by a metal-panel cladding system. Vertical post-tensioning tendons provide, in addition to overturning resistance, a “self-centering” capability in the event of an earthquake. In other words, the tower will right itself rather than fall to the ground. The concept is relatively new. The SFO tower is the tallest example of its use to date.
Given the stress and high levels of continuous concentration associated with the work of controllers, care was taken to engineer-in a certain degree of comfort. This took the form of stability at the work level for the controllers and for the sensitive instrumentation they work with. The self-centering factor is part of this equation, but not the only part. Approximately two-thirds of the way up the tower, attached on two sides, are two 40,000-lb concrete blocks that act as dampers. This further minimizes the tendency of such a tall, slender structure to sway in high winds, which are common in the Bay area.
Mission Critical & Secure
Air traffic control is mission-critical. Hence, the FAA has mandated certain secure design parameters, like blast design, for these facilities. The SFO tower rises above a three-story, 55,000-sf, shared-function office building. The building houses administrative offices for airport management and the FAA, along with computer equipment, back-up generators, and a secure passenger-transit corridor. Since the building is adjacent to a busy roadway used for passenger pick-up and drop-off, we engineered it to be blast resistant.
Our clients also identified LEED-certification as a goal. The entire complex is sensitive to the tenets of sustainability, making maximum use of daylighting and energy-efficient lighting and HVAC systems. Furthermore, the design-build concept, new though it is to this type of facility, not only reduced overall costs, but also enabled our team to keep to the project’s aggressive schedule. The FAA tested the facility over 12 months before its official completion.