August 10, 2000

More than meets the eye at 505 Union Station

One wall leans in at 15 degrees, another leans out at 4 degrees and the columns aren’t where they’re supposed to be -- how does Seattle's new 505 Union Station Building stand up?

505 Union Station leans at several different angles. Photo submitted by Coughlin Porter Lundeen.

The design of Vulcan Northwest’s new office building and corporate headquarters, demanded some fast, creative thinking on the part of structural engineer Coughlin Porter Lundeen.

The unusually angled walls defy the gravitational forces that hold a building upright. In perfect conditions, with no wind or earthquake, a building will stand with gravity systems alone, but the walls of this building put horizontal loads on the structure that would pull it over. To combat this, Terry Lundeen, structural principal in charge of the project, designed a primary braced frame system to withstand wind and earthquake conditions, and a secondary system of rigid frames to strengthen the existing column structure and resist the building’s own lateral pull. Sensitive to keeping the support systems out of the way of otherwise open office space, the horizontal forces are transferred back to the core from the building perimeter by means of special connections in the floor framing. This allows the perimeter columns to remain as thin and light as possible while the main load-bearing structures are hidden in the core of the building.

Again to preserve as much open space as possible on the office floors, Lundeen rejected the traditional approach of in-board columns with cantilevered slabs.

"The columns would have been in undesirable places on each floor and we wanted to maximize the amount of column-free space," he noted.

Instead Lundeen and his team opted for columns intricately woven into the curtain wall system. These columns are both sloped and skewed then curve at the top to become part of the roof structure and support skylights. There is no exposed metal on the north wall. All four sides of the glass panes are bonded with silicon to an aluminum frame, which in turn is bolted to the steel structure on each floor. The result is a spacious office environment with one giant window overlooking the downtown Seattle skyline.

The building’s complex system of transfers does not end with the lateral systems. The shape of 505 Union Station does not allow the support columns to sit directly on the perimeter concrete columns that hold up the lid of the existing parking garage beneath it. Lundeen designed a number of custom column transfers to carry the building’s weight back to the original parking garage columns.

Typically, new concrete walls provide the transfers between existing parking stalls, with little impact to either the building or garage. In a few locations, adding walls would have meant blocking a drive aisle or creating another obstruction. Instead, a system of steel members between the first and second floors transfers the weight to the garage columns.

The whole project was completed on a fast-track schedule established at the time the architectural scheme was picked. The steel structure is so integrated with the architectural design that architect NBBJ and Coughlin Porter Lundeen had some critical decisions to make very early in the process. Any change in the architectural design would have had a much bigger than usual impact on the structural design and steel purchasing. At the time, steel prices were about to rise sharply and the project would have cost significantly more if the bid had been delayed just a few weeks.

John Savo, NBBJ’s principal in charge of 505 Union Station, says collaboration was exceptionally important on this project.

"We needed a consultant team that would not only help us realize our vision, but would also push the envelope and bring fresh ideas to the table," Savo said. "We challenged each other to achieve greater heights than we could on our own."

505 Union Station is scheduled for completion this summer. The top five floors will be occupied by building owner Vulcan Northwest.

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