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January 27, 2014

National finalist: Gold award
Structural systems

Photo courtesy of Hart Crowser [enlarge]
Federal Center South is supported by thousands of timber piles left in place from a previous building.

Hart Crowser

Project: Federal Center South

Client: Sellen Construction

Federal Center South is the first of a coming wave of 21st-century government office buildings designed to optimize building materials, fit into the natural setting, minimize carbon footprints and provide a desirable work environment.

Design-build team member Hart Crowser adapted routine subsurface solutions to deliver more efficiency and better value to the client, and the eventual tenant: the U.S. Army Corps of Engineers, Seattle District.

Federal Center South will provide emergency response during and after a major disaster. It was imperative that the building withstand a major seismic event. By researching historical data of the site, Hart Crowser was able to provide a solution that adapted traditional subsurface elements.

The site was a former industrial area on the Duwamish Waterway, where soft soils deposited by thousands of years of flowing and flooding waters presented a challenging soil base.

The previous building on the site utilized thousands of timber piles, which were left in place for the new building. Stone columns with 4-foot-diameter shafts of gravel were used to increase the density of loose soils, reducing earthquake-related settlement and increasing foundational support. Hart Crowser redesigned the stone columns to provide a wall of densified soil along the waterway to stop a subterranean landslide that might be caused by weakened soils during a major earthquake.

To manage stormwater, Hart Crowser conducted infiltration tests in the field, leading to rain gardens and infiltration galleries. Water features, open flow and ponding areas were created to naturally divert, detain and infiltrate stormwater runoff. No stormwater drain pipes were installed as a result of creative stormwater-management design. Four acres of impermeable surfaces were converted to 50 percent pervious surfaces, promoting natural infiltration of precipitation.

Hart Crowser’s energy-efficiency methods have made Federal Center South a leading example of energy performance, putting it in the top 1 percent of U.S. office buildings.

Energy piles significantly reduced the need for conventional heating and cooling elements, and cut the carbon footprint of the building by more than 10 percent. Energy piles provide a low-cost method of using the constant temperature of the ground and the groundwater to help cool or warm the building, depending upon the season.

Installations typically represent about 80 percent of geothermal systems, but Hart Crowser looked forward and this cost was already built into the design through the foundation piles. The benefit is a return on investment in only three to four years, instead of the typical 10 to 12 years.

Federal Center South represents a model of successful design-build procurement for vertical construction in the public sector. Hart Crowser’s solutions met sustainability goals, overcame challenges involved with poor soil in an earthquake-prone area, and applied innovative engineering to traditional solutions. The result is a modern, highly efficient, 21st-century workplace for the tenant.

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