The American Concrete Institute (ACI) recognized the National Museum of the American Indian (NMAI) in Washington, D.C. as one of its notable projects and will feature it in the upcoming centennial publication, “Concrete - A Century of Innovation.” ACI selected the project for its complex forming and special concrete mixes.

A joint venture of The Clark Construction Group Inc. of Bethesda, MD, and Table Mountain Rancheria Enterprises of Friant, CA, is serving as general contractor on the $200-million project. Clark Concrete performed the work on the project.

Designed by a joint venture of the Polshek Partnership of New York, SmithGroup of Washington, D.C. and Jones and Jones of Seattle, WA, the structure includes 254,000-sq.-ft. (23,597 sq m) that features exhibit space, 300-seat theatre and two 50-seat educational workshop spaces. When the building is completed in fall 2004, it will resemble a natural rock formation sculpted by wind and water.

The Potomac Room is the centerpiece of the facility, and is highlighted by a 121-ft. (37 m) high dome ceiling, radial walls, and radial monumental staircases. The building structure also incorporates cantilevered slabs, some of which are hung from the floors above.

No two floors utilize the same geometric layout, and the design contains many compound curves and changing radii throughout the building.

Additionally, the elevated structural slabs were designed and installed with camber to accommodate slab deflections, resulting in flat and level floors. To undertake the challenge of constructing such a complex facility, Clark Concrete employed several different forming systems including European formwork systems made by Conesco Doka of Little Ferry, NJ.

Because the foundation walls are curved with no repetitive radii, the Conesco Doka adjustable radius formwork system was utilized for its flexibility. The adjustable system is capable of forming concave or convex surfaces with radii as tight as 10 ft. (3 m).

In addition, eight separate custom made shear wall forms were used to form the curved vertical shafts that house mechanical risers and stairways within the structure. The form systems used on the project ultimately increased productivity and helped control quality by rigidly maintaining the varying concave or convex radii for the different geometric configurations once the forms were set into place.

Due to space constraints, a majority of the formwork was assembled at an off-site fabrication shop. A separate crew produced the curved beam sides, slab edge forms, and other types of formwork from geometry drawings furnished by the field engineering crew. Once completed, the forms were broken down into segments and transported back to the job site, where they were then reassembled and put in place.

Clark Concrete utilized self-consolidating concrete for vertical placements. because of the size and complex shape of the walls and columns. The self-consolidating mix is much less viscous than normal concrete, which allows for easier placement, helps eliminate voids and honeycombs in areas where vibration is difficult, and results in a high-quality finish.

NMAI was one of the most challenging and complex cast in place concrete structures ever constructed by Clark Concrete.

“Concrete - A Century of Innovation” will be available in early 2004.

For more information, visit www.concrete.org. CEG

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