The $1.15-billion transformation of Seattle’s iconic KeyArena into the Climate Pledge Arena required keeping its 45-million-lb roof in place during construction and removing and replacing its curtain wall. As a result, the project posed challenges that were as difficult as they were unique, including supporting the roof in place with steel shoring because the excavation undermined its foundations.

The temporary steel, which also had to resist seismic loads and limit roof movement to ¼ in., cost $35 million and weighed 4,400 tons—also complicating the top-down construction. 

The team solved a major constructibility puzzle by figuring out how to locate the shoring so it would not interfere with the new seating bowl structure and could be cut out after it was no longer needed.

Crews first had to carefully remove the old curtain wall, store it offsite and strip it of contaminants. When the new structure was finished, crews reinstalled the curtain wall with its existing glass. As if the scope of the effort was not enough, COVID-19 hit. Mortenson, under a construction manager at-risk contract, worked quickly with its partners to devise and implement a response plan that would keep the project moving safely.

More than 680,000 cu yd of dirt was removed during the expanded arena’s excavation as temporary supports kept the existing iconic roof in place.
Photo courtesy Mortenson/Alex Fradkin

The arena is built for net-zero operational carbon, with use of electric power and other sustainability features. The project “becomes a model to ensure the sports and live entertainment industry continues down a path of more sustainable venues,” says Geoff Cheong, Populous senior principal.