New Arena at Seattle Center Roof Enters 'Floating' Phase

SEATTLE -- We all benefit from support systems in our lives. The historic landmark roof at New Arena at Seattle Center is no exception.
Workers are far into the process of erecting a total of more than 70 temporary steel columns to hold up the roof as the construction of the New Arena delves more than five stories below ground to build a brand-new arena.

Repeat: Brand-new arena. There is nothing remaining from what was built in 1962 for the World's Fair and remodeled and reopened in 1995.
Except that iconic roof. The steel columns will be paired, then secured with nearly 40 steel cross-beams for additional support as the New Arena goes subterranean. Many of the cross-beams and paired columns are in place on the north half, allowing the construction crew to anticipate the beginning of exaction late this month. The remaining columns and cross-beams will be in place by mid- to late November.

"Those [concrete] Y-columns and four chevrons [super-size buttresses] held up the roof [from 1962 until now]," says Ken Johnsen, construction executive for Oak View Group and NHL Seattle. "Underneath each one is a huge concrete block that we have to demolish and excavate."
The first of those concrete blocks has been drilled, chipped and generally pulverized so that one of those Y-columns now appears suspended in mid-air. More concrete blocks are under demolition. Each week this fall, it will seem increasingly that the entire roof is suspended in airspace.
But it won't be easy. There's a massive amount of concrete below each Y-column and the chevron under-blocks are, let's call it, eight to 10 times bigger than Y-column blocks.
Johnsen says the early blocks are revealing more rebar or a steel reinforcement cage-like material than anticipated. More-than-specified concrete has been poured for a number of blocks when compared with the 1962 plans.
"That first block is a learning process," says Johnsen. "You might realize a different piece of machinery would work better. You want to get into a rhythm and be more efficient [at demolishing the blocks]. It will take some work, we don't quite know how much work each one is going to be."

"Physics and jackhammering equipment are involved in the first step for removing the concrete behemoths," says Greg Huber, project executive for Mortenson, the New Arena's lead construction partner.
"Removing each block starts with jacking to alleviate pressure from the footings," says Huber during a recent tour with NHL Seattle, "so there is no gravity going down to the footings."
Completing the support system around the north half will allow structural engineers on the project to give a greenlight for excavating 600,000 cubic yards of dirt. Where Johnsen and Huber stood during a recent construction tour will be 15 feet lower underground in the weeks ahead.
By October, more Y-columns will be looking suspended in mid-air. By December, it will turn heads of any holiday season passersby. The roof will almost look like it is floating. But that support system of temporary steel columns and cross-beams will be firmly in place to enable subterranean construction to begin in 2020.