C+S May 2021 Vol. 7 Issue 5 (web)

Climate Pledge Arena An Environmental and Engineering Marvel By Greg Huber

Being chosen by Oak View Group, a Seattle public-private partner and developer, to redevelop the former Key Arena into a brand-new, best- in-world venue and the future home of National Hockey League's Seattle Kraken and Women's National Basketball Association’s Seattle Storm, all while keeping its historic landmarked roof intact, has been one of Mortenson’s most challenging and rewarding undertakings. As if this alone wasn’t enough of a challenge, a whole new bar was set when Jeff Bezos from Amazon tweeted in June 2020, “I’m excited to announce that Amazon has purchased the naming rights to the historic Seattle arena previously known as Key Arena. Instead of calling it Amazon Arena, we’re naming it Climate Pledge Arena as a regular reminder of the urgent need for climate action. It will be the first net zero carbon certified arena in the world, generate zero waste from operations and events, and unclaimed rainwater in the ice system to create the greenest ice in the NHL. #ClimatePledge.” At the time of that announcement, the project team had already care- fully planned every aspect of the arena. The structural foundations and building excavation were well on their way, the procurement team was ordering necessary construction components and discussions with local utility companies were underway about how to power the build- ing’s operational needs.

cubic yards of dirt underneath to substitute for the arena's Y-column and buttresses that held up the historic roof. This was held by seventy-two temporary roof support (TRS) steel columns; each founded 70 to 90 feet below the existing arena floor level. The TRS system also had to resist seismic loads and limit movement to a quarter inch. Mortenson used water jets to remove concrete from the base of the old columns which exposed the steel rebar to allow the team to safely cut and extend the column foundations that were supported nearly 100 feet below grade. The process occurred during most of 2019 and used nearly the amount of steel equal to a modern-day Major League Soccer stadium. Morten- son relied on intense team collaboration, top-down construction, and digital tools to simulate the built environment. And today, Climate Pledge Arena is standing on the original 20 Y-columns and four pronged-buttresses to hold up the roof, originally built for the 1962 Seattle World’s Fair.

Although sustainability was always an important feature to be incorporated into the project, this new goal – to create the first net Zero Carbon certified arena in the world – was the biggest challenge yet. Luckily, Mortenson and the entire team’s passion and competitive spirit drove them to determine how – not if – this could be done. The certification by the International Living Futures In- stitute is the most rigorous benchmark of sustainability in the building envi- ronment. It is the gold standard against which all others are measured. People from around the world use its regenera- tive design framework to create spaces that give more than they take. Structural Challenges The first major challenge was determin- ing how to “recycle” the 44-million- pound historic roof (designed by Se- attle architect Paul Thiry. Meanwhile, the construction crew excavated 600,000



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