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November 16, 2000

Perfecting Pier 56

  • Such unique engineering challenges are only to be found in Seattle.
    Coughlin Porter Lundeen

    Seattle has built a certain notoriety around its many unique, and sometimes controversial, structures. From the original Space Needle to the Experience Music Project and the future Seattle Public Library. Of all these interesting structures, some are quintessentially Seattle. Pier 56 is one such example, and as redevelopment fever spreads along our waterfront, this legacy is at last being re-imbued with the life and respect it so deserves.

    Pier 56
    Making connections to Pier 56 through the seawall.

    But bringing the piers back to life presents an unusual set of design challenges, many of which were not even a glimmer in the eye of the original turn of the century engineers.

    For example:

    • How do you pipe in enough power to fuel a high-tech modern office out beyond the seawall?

    • How do you bring a building suspended over 80 feet of water up to seismic compliance?

    • How do you preserve the original structural elements that define the space while adapting it to accommodate modern demands?

    As if that weren’t enough to think about, how do you keep it all moving with two different structural engineers, two different architects and a series of tenants to deal with?

    Due to the size and nature of the building, the existing power supply was nowhere near adequate, but running power out to an office suspended above Puget Sound is not a straightforward task. Coordinating extensively with SeaTrans (which owns the seawall) and Seattle City Light, engineers from Coughlin Porter Lundeen designed a new duct bank and a transformer vault that run beneath Alaskan Way. A second transformer vault and concrete encased duct bank were required on the pier itself. This was suspended from existing heavy timber building columns at the first floor.

    But the real fun started when the power had to be brought through the seawall and into the building. “SeaTrans, understandably, didn’t want us punching holes in their seawall,” explains Steve Porter, principal in charge of site civil design. The challenge was to get the joint approval of both Seattle City Light and SeaTrans and implement design in a very short time frame. “After some pretty thorough research and working closely with both parties, we were able to design an acceptable penetration through the wall. In the end, it was so successful that they used the same design for the Pier 70 redevelopment,” Porter said. The most interesting aspect of the design is a flexible seismic joint between the rigid seawall and the wall of the pier that accommodates the different behaviors of the land and the constantly moving pier. This joint also prevents the load from the pier transferring back into the seawall.

    The structural work on the building brought its own set of challenges. Elliott’s Oyster House restaurant remained open throughout the entire renovation. During the process architects from Mithun announced their intention to move into thier new office space and began collaborating with the engineers and shell and core architects, Daly & Associates.

    It was the job of John Schwartz, the project’s development manager, then with Martin Smith Inc., to keep the team together and the project moving. For Schwartz, a thorough knowledge of the site and a significant investment in site reconnaissance were key. There are challenges thrown up by a building over water that simply do not exist on land. “There are certain things you simply can’t do when you’re working out of a boat,” laughed Schwartz. “On top of that, in Puget Sound the tides have a huge impact on the ability to get work done. The work platform moves between 10 and 12 feet every five hours!”

    It should come as no surprise then that piers are not precision pieces of engineering. Measurement tolerances can vary between as much as two or three inches, rather than the fractions of an inch typical elsewhere. At the west end the building, was 10 inches out of plumb, the consequence of a ship collision in the ’40s. The predominantly timber pier structures also require very different connections from their landlubbing metal, steel and concrete cousins. “You get bigger and beefier everything so the approach is significantly different to land-based construction processes.” explained Schwartz.

    Above decks, the first task was to tie the whole building together and make it seismically sound. “The existing structure is beautiful and we used it as much as we could, while designing our new seismic systems to be as unobtrusive as possible,” said structural engineer Cory Hitzemann. Mithun wanted to preserve the open space to create a non-cellular, collaborative office environment. Hitzemann worked closely with them to place shear walls where they would be least disruptive. One forms the border between Mithun’s offices and some extra leasable space, another frames the edge of the lobby.

    A clever system of transfers enabled the engineers to keep the shear walls in the north third of the building on the upper floor. A low roof joist at the south end of the building is strapped to the heavy timber trusses in the elevated center part of the roof and from there the load is transferred to the shear walls. Other metal straps run the entire length of the building and are concealed beneath the new roofing and the second story flooring to minimize their impact on the aesthetics of the building.

    Shear walls were avoided on the first floor where they would interfere with the retail space. Instead, a steel- braced frame within the building leaves the storefront space open. The solution is flexible enough to allow door openings to move in the future.

    In support of Mithun’s commitment to sustainable building practices, the special design of operable windows eliminates the need for air-conditioning and takes full advantage of the available natural light. In a new building, the windows might be framed with a foot-deep wood header beam. In a renovation of this type, the height was limited at the exterior wall, so the engineers designed a steel angle detail that required only 3 inches below the existing roof joists, enabling them to maximize the window height.

    One of the building’s most interesting architectural features is the entrance to Mithun’s second story office. The office wall is a separate structure set behind the original exterior wall. To accommodate this feature, the engineers had to punch a large hole in the existing exterior wall. They used steel to strengthen the existing framing and concealed it within the architectural finishes wherever possible.

    The entire redevelopment was completed within a significantly compressed schedule. The termination of Mithun’s existing lease in downtown Seattle meant designers had to cut two months off the original occupancy date. Things were not helped when further dry rot was discovered in the primary building columns, requiring their replacement. When Mithun moved into its new space a temporary sheer frame held things up while replacements were made.

    Today Pier 56 is resplendent in its fresh new look. Elliott’s overflows with more diners than ever, and Mithun’s offices are the envy of the downtown worker. And everyone who worked on the project has an interesting story to tell.

    Jill Jago is marketing director for Seattle-based Coughlin Porter Lundeen.

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