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Mammoet installs bridge at Seattle-Tacoma International Airport


March 1, 2020
By Mammoet

Mammoet has successfully completed the transport and lift of an elevated pedestrian walkway for the future Seattle-Tacoma International Airport’s newest expansion,

Part of the airport’s $968 million expansion, the new bridge is only the second walkway in the world with suitable clearance for a Boeing 747 to taxi beneath.

Mammoet devised a suitable installation method for the 1,472-ton walkway using the accelerated bridge construction (ABC) method. With their specialized equipment, Mammoet transported and lifted the prefabricated bridge into place. This allowed for an exponentially faster turnaround time, whereas traditional construction methods would have caused significant disruptions to the airport over a prolonged period of time. The entire operation was completed over two nights while flight traffic was at its lowest to ensure minimal disruption to the airport’s schedule.

The walkway was transported using a total of 56 axle-lines of SPMTs in a four-point configuration, with one set of SPMTs at each corner. Mammoet’ s transport team taxied the load a total of three miles down the centre runway while shouldering runways remained open for incoming, and outgoing planes. Total transport time from the assembly area, to the final destination between accepting V-piers was just under three hours.

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Once in position under the piers, erection crews took over using four 900-ton steel frames that utilized a strand jack system. This was the first time these frames from the Netherlands have been used in the U.S. to control the systems cables which are regularly rerouted downward. In this case, it was required to keep them clear of the work area and ensure they did not interfere with the final weld process below. With approximately 1.5 inches of tolerance for a precise fit, the bridge span was hoisted into its final position, 22 metres from the ground, before being welded into place.

After nearly eight years of planning, design, and construction, the installation has created, at 900 feet long, the world’s longest pedestrian bridge span over an active airport taxi lane. The international arrivals facility is expected to open later in 2020 and alongside other improvements will help double the airport’s international passenger capacity to 2,600 per hour.