Blue Plains Advanced Wastewater Treatment Plant
5000 Overlook Avenue, SW
Dear Mr. Johnson:
During its meeting of 25 January 2005, the Commission reviewed a revised design for the cladding, bridging and elevators of the new Egg-shaped Digester Facility at the Blue Plains Advanced Wastewater Treatment Plant. The members had no objections to the revised elevations of the elevator towers that now feature metal panels that match the decorative skin on the digesters. Eliminating the brick facing on the towers was seen as an improvement that will perhaps result in some cost savings. They were also supportive of the revised cladding scheme on the egg-shaped digesters that simplified the decorative pattern of the metal skin.
The more streamlined design of the bridges connecting the top of the digesters was felt to be an improvement over the previous Victorian styled scheme. However, the members felt that the shape of these bridges should be more honest in their structural form and should reflect the forces that are inherent in such horizontal trusses. The Commission recommended the bottom splayed members of the bridge frame that appeared to touch the sides of the eggs be removed as these were not contributing to the actual structural support of the catwalks. In fact, where these pieces of the frame connect to the sides of the eggs present problems because they will not allow for the predicted differential displacement or settlement between the individual eggs.
The members also suggested that to revise the shape of the bridge that the inverted bowed-bottom chord of the truss could be made to splay outward from the center as it reached up to connect to the outer edges of the top cap of the eggs. This configuration would give the truss some additional structural stability and yet still be seen as a sculptural element supporting the catwalks.
The Commission looks forward to further review of this project and recommends submission of a revised concept that responds to the concerns expressed above. Our next meeting is scheduled for the 17th of March, with a submission deadline on the 3rd of March. As always, the staff is available should you require additional guidance.
/s/Frederick J. Lindstrom
Mr. Jerry N. Johnson
General Manager, DC Water and Sewer Authority
5000 Overlook Avenue, SW
Washington, DC 20032
cc: Avis M. Russell, DCWASA
Cynthia Giordano, Arnold and Porter
Suman Sorg, Sorg Associates