These 165,000-Pound Columns Will Heft a 38-Story Tower 85 Feet Off the Ground

A one-of-a-kind design that's worth standing beneath.

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Near the water in downtown Seattle, there's about to be a skyscaper unlike anything the city—and, well, the world—has seen. A 38-story tower will sit a full 85 feet off the ground, creating a open plaza beneath it, all thanks to the immense strength of the 20 steel and concrete columns that will support it.

Skanska USA’s 2+U project, designed by architectural firm Pickard Chilton, will give Seattle new office space, but the open-air 24,000-square-foot retail, arts, and cultural plaza underneath the tower is the real draw. That, and the 20 enormous columns that hold the tower aloft and ensure that under-the-tower oasis has enough room for its own two- and three-story buildings.

Owing to the slanting ground it's built on, the lifted tower provides between 65 and 85 feet of usable space below it. Composite columns, engineered by MKA and weighing between 69,000 and 165,400 pounds each, provide the needed structural support. Precast offsite in British Columbia, Canada, steel tubes were wrapped in a rebar cage and encased with precast concrete. After curing and sandblasting, the columns each made the roughly 130-mile trek south to Seattle. Most traversed the journey on 14-axel, 52-wheel trucks while eight that came in too heavy for Washington bridges were shipped through the waters of Puget Sound by boat.

The columns all arrived at the job site in the dead of night. “There was only one route we could figure to get those columns to the site because the trucks and trailers were so large and heavy,” says Murphy McCullough, executive vice president of Skanska USA commercial development. “We hired a logistical engineer just to figure out how to get the things to the site with clearances and turning radiuses and how we were going to pick them (with a crane). It was an extremely intense experience.”

Lifting the columns required not one but two 500-ton cranes because of the weight. Once each column was placed in the foundational Y support, it was bolted and welded into place. Each two-column Y design matched up with another to form a giant W across the base of the tower, creating both an aesthetic and functional space under the tower McCullough believes serves as a world’s first. After all the columns were installed, they were pumped full of more concrete and fitted with additional rebar to create enough strength to hold the tower above.

The collaboration between Skanska, Pickard Chilton and MKA ensured both the functional component of the column design, but also an architectural flare. “How do you create columns to hold up the building and be sculptural,” McCullough asks, “that took a long time to figure out.”

“The sight slopes, so we really wanted the experience to have a height and grand scale,” McCullough says. “We really wanted to make sure we could have this village down below the office building. If the office building was too low, it just wouldn’t have worked. It needed to have enough light and air through it to feel like a separate special urban village.”

The columns have all taken their position, allowing the office building, which starts at level seven, to start being constructed above. By the end of 2018, Skanska expects to finish the concrete and steel work and have the entire project complete in July 2019.

“The big reason for doing this was from a pure customer standpoint,” McCullough says. “If you have a very special building with an amenity base employees really want, you are much more apt to attract (labor) talent.” That is why Skanska expects to fill what it calls a retail, arts and cultural village in the 2+U project with local restaurants, cafes, bakeries and cultural experiences.

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