Mammoet Transports, Installs Airport’s 900’ Pedestrian Bridge 72’ Above Ground

March 5, 2020 -- Mammoet has successfully transported, lifted, and set a huge elevated enclosed walkway as part of a $968 million expansion at Seattle-Tacoma International Airport.

The walkway is only the second in the world set high enough for a Boeing 747 jumbo jet to taxi beneath. It’s part the airport’s expansion for its future facility for international arrivals.

Despite the challenges of working at an active airport, Mammoet devised a suitable installation method for the 1,472-ton walkway using the ABC accelerated bridge construction method that allowed exponentially faster turnaround. With its specialized equipment, Mammoet transported and lifted the prefabricated bridge into place. Traditional construction methods would have caused significant disruptions to the airport over a long time.

To minimize disruption to the airport’s schedule, the entire move-pick-set operation was completed over two nights while flight traffic was at its lowest. The walkway was transported using a total of 56 axle lines of SPMT in four-point configuration, with one set of SPMTs at each corner.

Mammoet’s transport team taxied the load 3 miles down the center runway while shouldering runways remained open. Transporting the walkway from the assembly area to its final destination between accepting V-piers took just under three hours.

Once the walkway was in position under the piers, erection crews used four 900-ton steel frames and a strand-jack system. It was the first time the frames from the Netherlands have been used in the United States to control the system’s cables, which are regularly rerouted downward.

In this case, it was needed in order to keep them clear of the work area and to ensure they didn't interfere with final welding of the bridge. With about 1.5” of tolerance for a precise fit, the bridge span was hoisted into final position 72’2” above a taxiway before being welded into place.

After nearly eight years of planning, designing, and construction, the installation created the world’s longest pedestrian bridge span over an active airport taxi lane.

The international arrivals facility is expected to open later in 2020. Along with other improvements, it will help double the airport’s international passenger capacity to 2,600 per hour.