With more than 35 million passengers streaming through its gates each year, Phoenix's Sky Harbor International Airport is one of the largest and busiest airports in the nation.

And with traffic projected to increase to nearly 60 million by 2015, airport officials are working to keep abreast of the growth and also deal with increased international traffic, with European carriers such as British Airways and Lufthansa offering non stop service to London and Frankfurt, Germany.

Crews from the Phoenix office of McCarthy Building Cos. are wrapping up work on one project designed to handle the growing international traffic load, a new, $16 million walkway for travelers arriving from overseas. The new walkway will provide increased security and smoother immigration and customs controls for international passengers.

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"The idea is to get the international passengers out of the terminal without them mixing with the domestic passengers," said Steve Rao, vice president of Phoenix-based DWL Architects + Planners Inc., which along with Phoenix-based APMI, designed the project.

"It turns into a hassle for the Transportation Safety Administration and U.S. Customs because international passengers get mixed in with domestic passengers and then they (agents) have to inspect all the bags."

The idea for the international passenger walkway was first proposed more than 10 years ago, but after the Sept. 11, 2001, terrorist attacks on America, work on the project was accelerated. Although the project isn't large in terms of dollars, the tight work site, logistics, security and the need to keep the airport up and running made the job complex for designers and builders.

"This is one of the tightest logistical challenges I have faced in 25 years of construction," said McCarthy project director Jim Meadows. "It's not the size of the job or the components. It's logistics, trying to fit this project in an existing airport while maintaining a secure envelope."

Crews could only work after 10 p.m. at night, and since Sky Harbor Boulevard divided the site in two, McCarthy had to construct a man-bridge over the road to get workers and tools between the two areas.

A very tight site with only 30 -ft. between the existing retaining wall and the road meant designers and contractors had to cantilever a four-story "vertical transport" building out over Sky Harbor Boulevard. The four-story building features four elevators and two escalators to move passengers from the below-grade walkway to the bridge spanning Sky Harbor Boulevard.

The vertical transport building features a sloped glass curtain wall with concrete columns angling out over the road below. Seamless stainless steel tubes encase the concrete columns, giving the structure a modern, clean look. Four, 5-ft.-dia. concrete columns support the building's entire weight.

"We wanted to throw in a little new twist and the sloped glazing adds more of an international flavor," Rao said. "We did try to relate a lot of the materials so they would be similar to the existing buildings."

The vertical transport building in Terminal 4 is connected to the "B" concourse with a 20-ft.-wide, 580-ft.-long, glass-enclosed walkway running parallel to Sky Harbor Boulevard. McCarthy excavated a tunnel underneath the gates, which brings passengers to the walkway.

"We tried to make the tunnel imprint as small as possible because there were quite a bit of utilities and we wanted to minimize interference with those existing utilities," said Tim Sepper of Phoenix-based structural engineers KPFF Engineers Inc.
Since the elevation of the walkway was below an existing retaining wall running along Sky Harbor Boulevard, contractors had to shore up the wall while tunneling and building the walkway. McCarthy subcontractor Bechco Inc. used concrete micro-piles drilled 30- ft. to 40- ft. vertically through the retaining wall's footing to shore it up. A landscaped strip will feature cactuses and other native plants once the project is finished.

If we hadn't stabilized that wall, when we excavated, it would have just come tumbling down," said McCarthy's Jeff Brown of McCarthy.

A 180-ft.-long bridge over Sky Harbor Boulevard brings passengers into the main area of Terminal Four. The bridge required construction of an 8-ft.-diameter. concrete column - on top of an electrical duct bank. The area was so tight that contractors had to knock the flanges off the concrete forms to fit the column in and cast it.

"Structurally, one of the most challenging parts of the project was threading the bridge through directly above some lower bridges," Sepper said. "We had a corner that curved over the loading dock, so there were very few locations to put columns in to support the bridge."

Contractors built grade beams underneath the duct bank and then spanned them with steel grillage and No. 11 rebar. The column was then built on top, although it is slightly off set.

Phoenix-based Able Steel fabricated and erected more than 180 tons of steel, while Azteca Electrical of Phoenix performed the wiring. T-PAC, also of Phoenix, placed 270 precast segments in the project, including a 60-ft.-long, 36-ton piece using a sliding counter balance beam to fit the segment between the existing structures above and below.

"It's not your typical building, it's not your typical bridge and it's not your typical tunnel," Sepper said. "It's all of those things in a tight, almost impossible site."