The SourceCivil Engineering MagazinePittsburgh draws inspiration for its “right-sized” airport

Pittsburgh draws inspiration for its “right-sized” airport

By T.R. Witcher

When Pittsburgh International Airport opened its last great modernization project in 1992, it was hailed as the airport of the future. The then-novel configuration divided the airport into two main structures — a landside terminal for check-ins, security screening, and baggage claims and an airside concourse with an X-shaped footprint that was in the middle of the landing field, where passengers would catch their planes. The two were joined by an underground automated people mover.

The airport design reflected the airport’s status as a hub airport for US Airways, and it was built with connecting passengers in mind. The X footprint allowed travelers to land at a gate in one leg, grab a coffee or book in the shops in the middle of the concourse, then conveniently head down another leg to make a connecting flight.     

For years the design was a success. In 2000, Pittsburgh saw nearly 21 million passengers, about 70% of whom were connecting. But September 11, 2001, changed the fortunes of the airport.

After the 9/11 attacks, US Airways went through two bankruptcies and ultimately decided to “de-hub” Pittsburgh in 2005. “That left us with a building designed for that connecting passenger (and) built for 32 million passengers,” says Paul Hoback, the chief development officer at the Allegheny County Airport Authority, which manages the Pittsburgh airport. But “we’re not that hub anymore,” he says.

The airport spent the next several years putting capital funds into maintaining facilities and upgrading runways but mainly focused on keeping the lights on. In 2015, the ACAA began a master plan to evaluate the future of the airport. With the need for the hub model gone, airport officials reconceived the airport as an “origin and destination” airport instead — one meant for, and catering to, local travelers.

bird's eye view
A new $1.39 billion terminal at Pittsburgh International Airport will combine the airport’s check-in, screening, and gate facilities into a single building designed for local travelers. (Courtesy of Gensler + HDR in association with luis vidal + architects)

The new, $1.39 billion Pittsburgh terminal project will construct a new terminal building that will adjoin the airside concourse and create one integrated building, eliminating the need for the underground automated people mover. The airport authority anticipates from 12 million to 18 million yearly travelers moving forward, so it will simultaneously shrink the number of gates from more than 70 to 51. The existing baggage system and people mover, which are nearing the end of their functional lives, will be retired.

Airport officials call this a plan to “right-size” the airport — an unusual move in an era in which airport projects are almost inevitably adding capacity.

“The primary goal of this program is increasing sustainability and ensuring predictable airline costs,” says Hoback. “The airlines are the ones who will back the debt associated with the project.”

Nature, technology, community

The airport authority, as well as the engineers and designers on this project, points to three elements — nature, technology, and community — as guiding principles during the development of the project’s design. 

“When you come to Pittsburgh and you land at the airport, the idea is to convey a specific sense of place and not an airport that could be anywhere,” says Bill Peduzzi, P.E., the aviation director for Omaha, Nebraska-based HDR and project manager for the site and infrastructure portion of the project’s terminal design team. “That informed the development of the concepts.”

The design of the airport takes its cues from two distinct features of Pittsburgh. The first is cultural and the second topographical.

airport roof
The roof of the airport is a series of undulating ribbon forms meant to evoke Pittsburgh’s hilly landscape. (Courtesy of Gensler + HDR in association with luis vidal + architects)

This is a town where family and friends not only drop you off and pick you up at the airport but also want to see you off. To accommodate them, designers fashioned a larger “meeter-greeter” hall than is typical. Gensler and HDR, in association with Madrid-based firm luis vidal + architects, devised a three-level terminal whose floor plates get smaller as they rise, much like a tiered wedding cake. (An expanded ground-level roadway will also have double curbs to provide more room for ride-share services for those who are arriving and departing on their own.)

The three-tiered design allowed designers to utilize “those leftover residual areas that would normally be flat roofs” and turn them into elevated, outdoor gardens, says Ty Osbaugh, AIA, LEED AP, an aviation practice area leader at Gensler. He says this could be a game changer in airport design. “People will now start to look at airports (as) not being these hermetically sealed interior buildings. Now they’re permeable. You can go actually go outside when you’re at the airport.”

With these outdoor gardens in place, designers doubled down on the motif by conceiving of the building, particularly its top-level arrivals hall, as a “pavilion in the forest.” The roof is a series of undulating ribbons, which create clerestories. “You start to read this mountainous environment that has little glimmers of population within it,” Osbaugh says, which mirrors the city’s hilly topography — there is no shortage of homes throughout the city that appear to be carved out of those hills.

Challenging columns

For the terminal’s interior columns, an internal research and development team at Thornton Tomasetti known as CORE studio devised a geometrically optimized bundled tube scheme to support the undulating roof.

Engineers at Thornton Tomasetti ran computer simulations to simplify the complex geometries of the branching tube columns that support the main arrival hall. (Courtesy of Gensler + HDR in association with luis vidal + architects)

The new building’s foundations will have to work around the existing automated people mover tunnel and two utility tunnels — 50 to 60 ft apart, each between 45 and 50 ft wide. These cut-and-cover tunnels will remain in operation during construction and are buried only about 8 ft under the tarmac apron.

During the tunnel’s construction, “they didn’t backfill in a way where you can build off it and utilize the soil” for future projects, says Thomas Poulos, P.E., S.E., a senior principal with Thornton Tomasetti. Poulos is the head of the firm’s aviation practice and lead engineer on the project. “There’s a big swath on the north and south ends of the tunnels that is inadequate to support our proposed foundations or the slab on grade,” he says. “Therefore, the supported slab needed to extend above the tunnels and beyond the backfilled areas.”

Thornton Tomasetti plans to use micropiles to support the new building columns in backfilled areas where the soil is weakest. Battered micropiles will resist lateral loading and keep the new terminal from loading the existing tunnels. (Caissons will be used in areas of better soil quality).

In addition, the design calls for 53 column transfers at the apron level to direct the new building’s column loads away from these tunnels. “The load was so heavy the concrete itself couldn’t carry it, so we had to supplement the concrete transfers by adding structural steel girders inside of them,” explains Poulos.

An underground automated people mover station, with a footprint of approximately 120 ft by 200 ft, is located at the end of the tunnels. The new two-story section of the terminal will be built directly atop this station. Poulos says it wasn’t cost-effective to transfer a load across 200 ft, so engineers instead devised a way to lighten the load on the station. “We replaced 4 ft of soil and apron with lightweight geofoam, which allows us additional capacity to support the new connector building and a new concourse entryway,” says Poulos. Hence, the existing station won’t see any more load than it saw originally, but it will be able to support a new two-story structure. A grillage of steel transfer girders will transfer the loads of the new columns to the existing station columns.

Building a bridge

After the iconic roof, the structure that visitors will notice the most is a two-level access bridge for vehicles. Its design is a nod to another signature aspect of the Pittsburgh terroir — its countless bridges.

A two-level, 1,300 ft long bridge will bring vehicles to the terminal. Engineers have devised slender columns to create visual harmony with the terminal building. (Courtesy of Gensler + HDR in association with luis vidal + architects)

“The airport is truly the front door to the region, and this is our front door,” says Hoback. “This is why we wanted this experience to be so special. Pittsburgh is the city of bridges. We needed this front door experience, to have a bridge that was special.”

The two-level, 45 ft tall bridge will be built over a ground-level roadway and founded on caissons. It will provide vehicles access to the exterior of the terminal.

Creating what effectively needed to be a heavy highway bridge that was also visually attractive with pedestrian elements, planters, and seats, was a challenge, says Kevin O’Connor, P.E., a senior project manager and the lead bridge engineer on the project for HDR. The resulting trapezoidal box-girder design for the 1,300 ft long bridge features no hammerhead columns or wall piers. Slender columns at the edges of the bridge match the design aesthetic and positioning of the terminal’s own columns.

The goal was to create a bridge that itself could become a destination. “We didn’t want to obstruct the view of building, (but) at the same time the bridge must carry highway loads and have very tight movement tolerances due to its adjacency to the terminal entrances,” says HDR’s Peduzzi. 

An airport for the post-COVID world

The airport addition was expected to break ground last year, but then COVID-19 struck. In April 2020, passenger counts had cratered to about 5% of their usual levels. “I can’t tell you we didn’t sweat a little bit,” says Hoback. “But we also looked at this from a long-term perspective.”

The delay allowed designers to plan for a post-pandemic world. According to Hoback, the airport is testing a variety of “touchless passenger journey” features, including “wave to call” elevators, foot pedals that operate doors, and antimicrobial copper film installed where touching of surfaces is required. The airport is also testing sensors that can provide “real-time access to indoor air quality information and restroom cleaning information,” says Hoback, as well as potentially providing this information to employees and passengers through dashboards around the terminal.

Construction is set to begin in the fall and is scheduled to be complete in late 2024, with commissioning and testing going through the end of 2024. The new terminal building is expected to open in early 2025.

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