Mammoet has again challenged racing against time with the installation of an elevated pedestrian walkway bridge at Seattle-Tacoma Airport in the United States. The entire operation was carried out at the airport’s new arrivals facility – while runways on either side remained open to air traffic.
The prefabricated walkway, part of the airport’s US$968 million expansion, weighed 1,472 US tons (1,335 tonnes). Mammoet used 56 axle-lines of self-propelled modular transporter (SPMT) in a four-point configuration, with one set of SPMT at each corner, moving the structure down the airport’s central runway from the assembly area to its installation location which is 3 miles (5 km) away.
The total transport movement took less than three hours, Mammoet positioned the walkway between two of the airport’s piers, where the erection crews took over. The crews used a strand jack system with four 900 ton steel frames to lift the prefabricated structure.
With just a mere 1.5 inch (38mm) tolerance for a precise fit, it was then welded into place between the two piers at a height of 22 metres above the ground.
The transport and installation of the walkway was done at night when the airport traffic was the lowest. This minimized disruption at the airport with the entire operation completed in just two nights.
The newly-installed walkway is the only second in the world with enough space to allow a Boeing 747 aircraft to pass beneath it. Seattle-Tacoma’s international arrivals facility is scheduled to open in the second half of 2020 and expecting international passenger capacity doubled to 2,600 people per hour.