Hartsfield-Jackson Atlanta International Airport Concourse D is one of the original five concourses of Hartsfield-Jackson Atlanta International Airport’s Central Passenger Terminal Complex, which opened in 1980. The nearly 50-year-old concourse was meant to serve smaller planes. But in Hartsfield’s meteoric rise to becoming the world’s busiest airport, the concourse grew increasingly cramped.
Driving the issue was “the bigger planes that are now making their way into the fleet mix for the airlines – you’re talking about the 737, the (Airbus) A321; those can take up to about 190 to 200 passengers, depending on how they are configured,” said Edmund Ramos, vice president of aviation delivery at WSP in the U.S., the engineering and design firm handling the concourse’s expansion. (WSP is part of a joint venture, with H.J. Russell & Co. and Turner & Townsend providing program management support services for the city of Atlanta’s $18 billion capital improvement program.)
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D was crowded for passengers and planes, and the building needed to be upgraded to modern seismic codes.
The new $1.3 billion Concourse D, scheduled for completion in 2029, will expand by 75%. Cramped holding rooms will double in size, and restrooms and concession spaces will also grow. The building’s ceiling will jump from 11 feet to 18 feet, and the width of the concourse will expand from 60 feet to 99 feet – with the circulation area along the spine of the concourse widening from 18 feet to 29 feet. Finally, Concourse D will lengthen by 288 feet – 192 feet on the north side and 96 feet to the south.
The gate count will drop from 40 to 34, but passenger-processing capacity will increase – D will be able to hold a thousand more passengers at any given time.
But how do you expand a busy concourse without shutting it down completely? “Our airline partners aren’t interested in shutting down the entire concourse,” Ramos said. Instead, the airport allowed the project team to close eight gates at a time.
WSP collaborated with the airport, structural engineering firm Thornton Tomasetti, Sykes Consulting, and Holder-Moody-Bryson-Sovereign (known as HMBS, a joint venture contractor) to find a solution. “We were all sitting in a room talking about, ‘How do we do this?’” said Mary Williams, P.E., S.E., associate principal in Thornton Tomasetti’s Chicago office.
“We looked at just stick-building it, working three shifts, we looked at a lot of things, and I would say modular just almost became a no-brainer after that,” said Todd McClendon, senior vice president of aviation engineering at WSP in the U.S.
2 construction zones
Engineers settled on a plan to expand Concourse D with modules built on-site. In the first phase of work, the north pier of Concourse D was expanded eastward with five modules. These will eventually serve as holding rooms in the finished concourse; during the expansion, they will also serve as temporary circulation corridors to move passengers through the concourse.
“It was really innovative to say, ‘We’re going to build on one side and march around the building and take gates as we go,’” Williams said. “And then as we move along, we move the modules, then those gates open, then we close the next gates, then we move the modules, and we open those gates, and then we keep marching around. This made you think outside the box; it made you reinvent the engineering approach.”
Construction on the first of 10 modules began in December 2023 on a secured “modular yard” on the airport grounds, a mile from Concourse D. At the same time, another crew was saw-cutting the existing pavement adjacent to the concourse to start foundation work. By March 2024, five of the modules were complete – with exterior skin and glass as well as the mechanical, electrical, and plumbing rough-ins.
The project used two survey crews and a surveyor to double-check the work of both crews, ensuring that the modules would fit the foundations.
Due to seismic considerations, the columns could not be spliced, so they had to be anchored to a temporary foundation at the mod bar, then disconnected, transported, and installed in their final foundations adjacent the concourse. “We had a bolted connection with an angle that allowed us just to pick the I-frame column and then reconnect it via a weld (at the concourse site),” McClendon said. The tolerances were unforgiving: “We had to be within three-sixteens (to) a quarter of an inch.”
Moving the modules
But how to move these modules – the longest of which measured 192 feet long by 35 feet wide? This is where Dutch-firm Mammoet’s massive self-propelled modular transporters came in.
Beginning in April 2024, a pair of transporters were driven under each of the first five modules, which were in turn lifted 18 inches off their temporary foundations, then transported to the concourse. (The lumbering SPMTs took 50 minutes to complete the 1-mile journey, then crab-walked each module to within 3.5 inches of the concourse.)
Typical construction does not require buildings to be designed for a lifted condition. Through all this coordination, these modules were designed to be lifted. “There’s an inherent softness in a building when you lift it up,” Williams said. “And so we found that we had to actually install temporary bracing to provide some stiffness, so the loads went where we wanted them to go and the deflection of the structure was within acceptable limits.”
The SPMTs supported the modules, which weighed from 400 tons to more than 700 tons, on hydraulic zones that were calibrated to ensure the loads stayed balanced during transport. While the axles on an SPMT can move up and down to keep its cargo flat, engineers had to carefully study the variability in the surface of the tarmac and calculate load requirements as well as module sizes.
Hartsfield-Jackson Atlanta International Airport“We realized that you don’t want just one singular SPMT underneath these modules because a single support point would create a condition like a teeter-totter,” Williams said. “You don’t want it to be unstable. You want two support points. So we had two parallel SPMTs on the boxcars, and we ended up having two underneath the 48-foot-wide configuration of the north tip modules as well.”
The engineering teams even developed a 70-page playbook to anticipate every potential problem of transporting modules across runways and taxiways, which were closed for the late-night moves – accounting for the possibility of flat tires, a shortage of spare parts, malfunctioning computer modules, and even bad weather.
The move could only be made if the site had 200 feet of visibility with winds below 25 mph. “The last thing we want,” Ramos said, “is we’re right there in the middle of the longest runway and you’ve got a plane about to land or take off at the world’s busiest airport.”
Aligning with the concourse foundation
There was still a final challenge: “How do we move a module that has numerous columns over to a new location and get it to line up with anchor rods and ensure that you can lower it without having clashes with the anchor rods?” Williams said. “We very quickly realized we shouldn’t be lowering it onto anchor rods. We set base plates and had the anchor rods installed already at the concourse side, and so we were just lowering the column, and the column got welded directly to that base plate instead so that you had a larger area to hit and you weren’t dependent on the tolerance of the anchor rods themselves.”
The first five modules were moved over the course of five weeks in spring 2024, and that portion of the concourse opened in September. The second five modules – which form the bulk of the extension of the north pier of Concourse D – were moved earlier this year; the extension of the north end will open in the fall. Construction will begin on the south pier of Concourse D next year. The project is slated to be completed by summer 2029.
