World’s Longest Pedestrian Walkway Over an Active Airport Taxi Lane Erected at Sea-Tac

Seattle Tacoma International Airport (Sea-Tac) is the 8th busiest airport in the U.S. with rapidly increasing passengers traffic each year. Of its 51.8 million passengers last year, 5.7 million were international travelers – a 15% increase from 2014. Clark Construction Group is working with the Port of Seattle to design and build a new International Arrivals Facility (IAF) to efficiently welcome those travelers to the Pacific Northwest. 

A prominent and iconic feature of the IAF project is an elevated pedestrian walkway over an active airport taxi lane, connecting Sea-Tac’s South Satellite to the new International Arrivals Hall. The glass and steel structure, when complete, will provide travelers with a breathtaking welcome to the region with expansive views of the Pacific Northwest landscape, including Mt. Rainier, as well as views of airplanes taxing below. 

This is only the third structure of its kind at an airport, and, at 780 feet, the longest walkway structure over an active taxi lane in the world. When tipped on its end, the walkway measures 150 taller than the Seattle Space Needle. It allows for 85 feet of vertical clearance and has a 610-foot clear span between footings — enough room for large, wide-body aircraft, such as a 747, to taxi beneath. 

Hoisting the 3-million-pound center span into place was another technically complex maneuver that 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 adjusted the walkway’s side spans to account for the weight of the center section, projecting a deflection of 7¾ inches once the structure was fully loaded. Using four strand jacks anchored to each end span connection, they hoisted the walkway to its final position 85 feet above the airport’s taxi lane. The strand jacks provided the steady strength needed to move the massive structure upward and gave the team greater control over the lift. The team’s precise calculations ensured the structure came together seamlessly, without the need for further adjustment. 

Sea-Tac, Seattle Tacoma International Airport, Clark Construction Group, KPFF, Skidmore Owings & Merrill, The Erection Company, Supreme Steel, Mammoet, Port of Seattle, KCE Structural Engineers

Clark leveraged cutting-edge survey technology to ensure quality, safety, and the success of the move and lift operations, and engaged third-party experts, including world-renowned structural engineer Allyn Kilsheimer of KCE Structural Engineers to validate the team’s technical approach. Clark’s in-house field engineering team used laser scanning of the walkway and end span connections, and Sea-Tac’s center runway, to understand existing conditions. With engineering tolerances between the side and center spans as small as 1 inch, it was imperative to understand how the three major sections of the walkway would come together before they were connected on site. As a result of the team’s precise planning, they achieved a fit-up within 3/16 of an inch, enabling the walkway lift to occur without interruption. 

Delivering this signature element of the overall IAF program required a complex and detailed technical plan and high degree of collaboration among the industry’s top construction, engineering, transport, and erection professionals, as well as extensive coordination with Sea-Tac’s airport operations team, the FAA, and TSA to minimize the impact to ongoing airport activities. 

Key stakeholders involved in the walkway’s design and construction include:

  • Clark Construction Group – Design-Builder
  • KPFF – Engineer of Record / Structural Engineer
  • Skidmore, Owings & Merrill – IAF Designer
  • The Erection Company (TEC) – Walkway Erector
  • Supreme Steel – Steel Fabricator
  • Mammoet – Heavy Transport
  • Port of Seattle – Client
  • KCE Structural Engineers – Peer Review
Sea-Tac, Seattle Tacoma International Airport, Clark Construction Group, KPFF, Skidmore Owings & Merrill, The Erection Company, Supreme Steel, Mammoet, Port of Seattle, KCE Structural Engineers