The Cradle Theater's elliptical shape required pouring more square feet of wall than deck.
BENJY BULLARD/CLARK CONCRETE CONTRACTORS The Cradle Theater's elliptical shape required pouring more square feet of wall than deck.

The Arena Stage renovation project in Washington, D.C., presented Clark Concrete Contractors, Bethesda, Md., with unusual challenges: In addition to renovating two theaters and constructing a new elliptically shaped theater that involved complex concrete designs, the company had to consider acoustics in the design plans.

The Washington Drama Society, owner of the Arena Stage, moved to another location while its buildings underwent this 29-month, 200,000-square-foot renovation. The project includes renovating the site's two existing theaters—the Kreeger and Fichandler—building the new Arlene and Robert Kogod Cradle Theater, and creating a lobby and administrative/support facilities to serve all three. With 250,000 square feet of wall forming and 140,000 square feet of horizontal elevated deck, this project is unlike most others, as typical projects have more deck than wall construction.

Specifically, the Cradle Theater provided Clark Concrete its biggest challenge. The oval-shaped building will seat 200 people and support the roof for the lobby area. To create the ellipse, Clark Concrete used cast-in-place concrete poured at a four-degree outward slope along the lines of eight different ellipse layouts and one radius layout. Special formwork created the unusual shape, including a circular wall formwork panel that normally is used for structures such as nuclear power plants. To create the ellipse, the curve moved following each pour. To accommodate the additional formwork necessary at the tops of the walls, Clark Concrete chose custom triangular filler panels.

Because of their unique shape, the 80x500-foot walls were poured before the decks, which led to another challenge: Because of acoustics, the slab had to be poured independently of the walls. The slab rests on neoprene pads mounted to steel brackets welded to large embeds located in the concrete walls. The curved wall shape made placing the embeds tricky and tedious, since embeds had to be placed in lifts of wall before they were poured to accommodate the four 36-foot column rebar cages that were located above and below each one.

The expansion of the other two theaters presented other challenges, including maintaining the acoustic integrity of the buildings while making the necessary changes. Renovations to the Fichandler Theater included new interior foundations, slab-on-grade elevated seating, and a slab-on-metal-deck raised floor. Cast-in-place concrete was used to build a four-level addition onto the Kreeger Theater, as well as a belowgrade parking structure.

To maintain the existing buildings' acoustic qualities, construction included acoustic isolation joints between theater and support structure walls. To separate belowgrade theater walls from support structures, such as offices or mechanical or electric rooms, Clark Concrete placed neoprene pads between the new and existing walls to limit possible vibrations. Abovegrade acoustic isolation joints were created by leaving a 3-inch air gap between the new and existing walls. Pouring new walls so close to the current ones required special formwork. The inner formwork was made of only plywood spaced off from the theater with thin strips of plastic foam. When it was time to remove the forms, the foam was knocked out and the plywood was removed, leaving the proper amount of space between the walls.

The area surrounding the theaters is receiving a makeover as well, complete with complex concrete designs that use cast-in-place concrete. Radial and chorded beams will surround the buildings' perimeter. A staircase wrapped around a 40-foot angled wall will create a new entrance to the theater, and a new large lobby including a number of ramps, stairs, and gradual slopes will allow theatergoers to access all three theaters from this shared area.

The Washington Drama Society will move back into its renovated home in 2010, when the $100 million project is complete.