The troubles experiencing the venture group on the $968 million Intercontinental Arrivals Facility venture at Seattle-Tacoma Intercontinental Airport could barely have been much more intense.

Topping the list of issues on the task was a middle-of-the-night installation of a 3 million-pound glass and steel walkway during driving rain when Boeing 747s landed and taxied nearby.

The 780-foot-lengthy walkway, with 85 ft of vertical clearance and a 610-foot-lengthy clear span between footings —​adequate room for vast-entire body plane to taxi underneath — was intended to link the airport’s South Satellite building to the new Intercontinental Arrivals corridor.

Transferring and hoisting the walkway’s 320-foot-lengthy center segment into put was a complex endeavor that necessary months of setting up, higher-tech resources and coordination between all stakeholders.

In purchase to enhance basic safety and minimize the impact to ongoing airport functions, the span was fabricated at a nearby airport cargo area. This technique enabled the group to streamline fabrication attempts, troubleshoot opportunity issues and carry out sensitive functions, these as the installation of the walkway’s remain cables, in a managed atmosphere, according to Brad McDermott, project government at Clark Design, the project’s design and style-builder. 

When the significant structure was full, Clark utilized self-propelled modular transportation equipment (SPMTs) operated by large transportation marketing consultant Mammoet to go it on to the tarmac. The specifically intended hydraulic trailers can go in any way and characteristic axles that telescope independently of one yet another to help evenly distribute excess weight and hold hundreds flat when transferring above uneven terrain, McDermott told Design Dive. Mammoet operating engineers managed the SPMTs via remote, walking immediately behind the transportation during the go.

Undertaking group

Style-Builder  Clark Design Group
Engineer of History / Structural Engineer  KPFF
IAF designer  Skidmore, Owings & Merrill
Walkway erector  The Erection Co. (TEC)
Steel fabricator  Supreme Steel
Hefty transportation engineer  Mammoet
Peer evaluation organization  KCE Structural Engineers

Spotters, in a convoy of cars in front and back again of the transportation, as very well as walking on foot, also accompanied the center span as it navigated the circuitous 3-mile route from the cargo area down the airport’s center runway to the IAF ​at walking velocity. The operator and all users of the go group maintained ongoing radio communication through the total operation, McDermott stated.

The painstaking a few-and-a-50 %-hour operation took put just after midnight during intervals of large rain and as airplanes taxied, landed, and took off on nearby runways. 

“We knew that any main movement to the steel assembly could end result in stress to the structure,” he stated. “We desired a transportation option for the walkway’s center span that provided a harmless, stable experience from starting to finish. The SPMTs helped us reach that purpose.”

Tech requires off

To smooth the way for the transportation, the organization leveraged what it states is cutting-edge survey technology to assess current disorders on the web site, such as laser scanning the walkway’s center and finish span connections and the airport’s center runway. The scans permitted the group to detect essential stake factors together the runway that introduced large cross-slopes or elevation changes. 

For the duration of the transportation, the group monitored much more than 100 strain gauges, which ended up attached to the center span steel to measure strains on the span these as bending or stretching. The gauges sent authentic-time details that the group measured and as opposed to the threshold boundaries predicted by structural engineers from KPFF.

Self-propelled modular transportation equipment moved the center span on to the tarmac.

Clark Design


“It was important for the venture group to detect the variations in elevation and cross-slopes of the runway, specifically at the taxiways between runways, in purchase to completely recognize how the transportation route would impact the center span during its go,” McDermott stated. “Next considerable evaluation of the survey details, the venture group elected to stiffen the momentary steel aid design and style even even further, earning the center span much more rigid.”

At the time the transportation was full, the hoisting operation commenced. Crews leveraged the walkway’s finish spans to aid the excess weight of the elevate. Using 4 strand jacks anchored to each and every finish span connection, they hoisted the walkway to its final place 85 ft earlier mentioned the airport’s taxi lane. The strand jacks provided the regular energy desired to go the significant structure upward and provided larger manage above the elevate. 

With engineering tolerances between the center and facet spans as modest as one inch, there was no room for error, McDermott stated. 

“We knew we had to get this correct the initially time,” he stated. 

Clark’s digital design and style and design and area engineering teams relied on laser scanning and animation to help visualize the total procedure ahead of time, from fabrication and transportation to the elevate operation. The laser scans developed applying Autodesk/Navisworks and Recap Pro provided what the group stated ended up being exact as-crafted details, which it utilized to validate that the many phases of fabrication remained in the tolerances of the design and style.

Strand jacks anchored to each and every finish of the span helped hoist the walkway to its final place 85 ft in the air. 

Clark Design


Animations applying Bentley Systems’ Synchro application thorough the sequence of work ahead of time. This was crucial due to the fact the team’s purpose was to limit the impact to airport functions, so there was extremely confined laydown area to work in, McDermott stated.

“The Synchro animation helped the group build and check their sequencing logic to make sure they minimized the impact to the airport and airways,” he stated. “The animation also served as a software to talk their strategy to venture stakeholders.”

Other application utilized on the venture included Leica Cyclone laser scan registration and Strain Gauges micro-measurements from Vishay Precision Group (VSG). Because the IAF project and pedestrian walkway are being manufactured at an lively airport, drones ended up not an selection, he stated. 

Environment report

Thanks to progress setting up, technology and collaboration between all stakeholders, the structure arrived with each other seamlessly with out the want for even further adjustment, McDermott stated. Very last 7 days, the taxi lane beneath the walkway reopened, enabling plane website traffic total obtain under the significant structure.

Now completely supported, the walkway is the world’s longest pedestrian bridge above an lively airport taxi lane, eclipsing London’s Gatwick Airport’s Pier 6 Connector by a hundred and twenty ft. Clark and trade lover The Erection Co. will go on welding functions on the walkway and start off exterior cladding work this spring with the purpose of completing the walkway structure and Intercontinental Arrivals Facility this drop. 

In the finish, technology was an essential component in the achievement of the venture but it did not exchange the collaborative work of the group, McDermott noted.

“Technology served to heighten setting up, high quality, and basic safety, but it was the team’s lifestyle of relentless setting up that in the long run ensured the exact execution of work,” he stated.