Clark Construction Group has built the world’s longest pedestrian walkway over an active airport taxi lane at Seattle-Tacoma International Airport.
The steel structure, which is 780ft-long (238m) and has 85ft (26m) of vertical clearance – enough room for wide-body aircraft to travel underneath – is a signature element of Sea-Tac’s new International Arrivals Facility (IAF). Clark Construction Group is leading design-build efforts on the US$968m capital project, which is among the largest and most complex ever undertaken at the airport.
One of three primary structural components, the walkway’s center span measures 320ft (98m) and weighs more than 1,500 tons. Clark prefabricated this section of the walkway at an airport cargo area three miles (4.8km) north of the IAF, to improve work area safety and minimize the impact to ongoing airport operations. This approach enabled the team to streamline fabrication efforts and provided them with the ability to identify and troubleshoot potential challenges off-site. It also enabled them to perform sensitive operations, such as the installation of the walkway’s stay cables, in a controlled environment.
Once prefabrication work was complete and the center span was fully loaded with its glass and metal panel façade, Clark moved it into place using self-propelled modular transportation devices (SPMTs) operated by heavy transportation expert Mammoet.
Traveling at walking speed, and with a caravan of escorts, it took three and a half hours to move the structure down the airport’s center runway to the IAF. The operation took place during periods of heavy rain and as airplanes taxied, landed, and took off on nearby runways.
Hoisting the center span into place demanded meticulous execution. Erection crews leveraged the walkway’s end spans to support the weight of the lift. Prior to the lift, structural engineer KPFF – one of three on the project, along with Skidmore, Owings & Merrill and Schlaich Bergermann – adjusted the walkway’s side spans to account for the weight of the center section. Using four strand jacks anchored to each end span connection, they hoisted the walkway to its final position.
Video courtesy of Clark Construction/Port of Seattle
