Building Team
Owner: U.S. General Services Administration, Northwest/Arctic Region
Architect: ZGF Architects LLP, Seattle
Structural Engineer: KPFF Consulting Engineers, Seattle*
General Contractor: Sellen Construction, Seattle
*Firm that entered project in IDEAS2 contest
Recently completed by the U.S. General Services Administration (GSA) for the Seattle District of the U.S. Army Corps of Engineers (USACE), the Federal Center South Building 1202 transforms a 4.6?acre brownfield site into a highly flexible and sustainable 209,000-sq.-ft regional headquarters.
The building, which meets USACE’s need for a more productive and collaborative workspace, fostering teamwork and efficiency, utilized steel to creatively solve a number of specific program criteria and site challenges:
• A perimeter diagrid to defend against progressive collapse
• Architecturally exposed floor framing synchronized with mechanical, lighting, and acoustical
• Ceiling solutions
• Integrated steel and reclaimed timber floor framing in the building’s “Commons”
• Blast protection at the building envelope
• “Energy Piles”
Building 1202 is the result of responding to both the 2009 American Recovery and Reinvestment Act (ARRA), which focused on improving our nation’s infrastructure and creating jobs, and the GSA’s Design Excellence program, which establishes nationwide procedures for selecting the finest architects and integrated design teams for GSA commissions. Building 1202 was planned, designed, and constructed in less than two and a half years, and stayed within its original $68 million design and construction budget.
The design organizes functions into two distinct forms, each with their own structural system and innovative approach. Open offices take shape around an oxbow-shaped exposed steel structure and perimeter diagrid. In the central core, conference and teaming rooms are constructed of reclaimed lumber and an innovative composite wood and concrete assembly supported on steel girders. These diverse structural systems not only meet the demanding structural requirements, but are also key contributors to the overall architectural expression and performance of the project.
The building’s form pays tribute to the site; Building 1202 is located at one of the last remaining oxbows of the original Duwamish Waterway and is actually situated on fill deposited when the Corps dredged and straightened the waterway in the early 1900s.
A perimeter diagrid was employed to serve against the progressive collapse design requirement. The diagrid consists of sloping columns and spandrel beams with bolted (pinned) connections between the members that creates an efficient and inherently redundant structure.
Compared to a conventional moment frame approach for solving progressive collapse, the diagrid
system achieved economy (and used less labor) by:
• Eliminating pile foundations.
• Reducing the steel tonnage by 30%.
• Accelerating erection.
• Eliminating full penetration welds at connections between the spandrels and the columns.
• Achieving smooth transitions through the curved portions of the building, facilitated with the diagrid by utilizing a tangential variation at each floor line. This allows the exterior skin to easily transition through the corners of the U?shape, resulting in a smoother appearance. The diagrid is painted white throughout in order to assist in diffusing both natural and artificial light inside the building, but also to be prominently visible through the exterior glazing.
The diagrid is celebrated as an integral part of the building’s architectural expression as well as a physical manifestation of the Corps’ motto of “Building Strong.”
Since the steel floor framing is exposed, the layout of the steel members was synchronized with the work station sizes and the ceiling solutions for the lighting, chilled beams (mechanical system), and acoustics.
Steel girders and connection materials were integrated with an innovative composite timber?concrete beam framing system in the central “Commons.” The wood was reclaimed from a warehouse that previously occupied the site (300,000 board feet of timber was reclaimed). Steel and timber were also integrated on the stairs and pedestrian bridges.
Steel framing was used in combination with light-gauge steel to resist blast loads on the building’s perimeter envelope. The steel trusses in the atrium were also design to meet blast requirements. The building is supported by 205 steel pipe piles that extend through soft, liquefaction?prone fill and alluvial soil. The piles are 150-ft to 175 ft long, and derive support in dense glacial soil -- 135 of the piles contain ground source heat exchange loops, creating “Energy Piles” that form the backbone of a geothermal system that works in concert with the building’s high-performance mechanical systems. This is one of the first projects in the region to combine the use of geothermal heating and cooling systems with structural piles.
Extensive 3D BIM modeling was performed to identify and resolve issues between the design disciplines prior to construction. These models were merged on a weekly basis in order to check design progress, resolve clash detection issues, and facilitate design decisions. Once construction began, the model served as a common tool that field trades used for communication and issue resolution.
The structural engineer was co?located at both the architects’ offices and steel detailers’ office to fully optimize communication and coordination between the design and construction team.
On?site prefabrication was used for the exterior wall panels and other building components. The team also utilized an existing on?site warehouse to build mock?ups of the building, including the interior office space, complete with structural, mechanical, and lighting systems.
The project exceeds or meets the owner’s program and aggressive sustainability and high?performance goals. Due to costs savings resulting from collaboration and design efficiency, a number enhancements were provided, including the Energy Piles and the potential for a rooftop PV array. The building has achieved LEED Gold status and ranks in the top 1% of energy?efficient buildings in the U.S.”