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By Nancy B. Solomon, AIA

Through a combination of grand stairs and public elevators, the new circulation space navigates a 21-foot drop in elevation between the historic street entrance at Mount Vernon Place and the new door to the campus's interior plaza. A new one-story addition between the original Conservatory building and the renovated row of 19th-century structures provides an accessible route, plus gallery space, from Washington Place to the arcade's plaza entrance. Improved vertical circulation at the south end of the arcade offers a more direct and appropriate passageway for patrons parking below grade. This same route also provides access to new practice spaces that were inserted underneath the plaza, adjacent to the garage.

Inserting the arcade's relatively light structure into the original buildings' massive brick walls was relatively easy, but nonetheless required some technical maneuvering. Explains project manager Carl Elefante, AIA, the Conservatory and Library buildings had been built according to different structural rhythms. "We built the arcade according to the library's 12-foot module because it was more regular, and because we wanted to leave the Library's brick wall and stack-room fenestration exposed." But, because of the Conservatory's own internal load conditions, the corresponding locations on its exterior brick wall were not necessarily well suited to handle any additional vertical load. A new steel ledger beam, therefore, had to be hung from the Conservatory wall to transfer loads to more appropriate points. Architecturally this was not a problem, as the designers planned to cover the Conservatory's brick wall (whose original fenestration had been sealed years ago to darken the interior performance space) with acoustical insulation (to isolate the concert hall) and drywall. The arcade's new steel trusses are fixed into beam pockets created in the Library's brick wall and rest on slip joints on the new ledger beam of the Conservatory wall, to accommodate thermal expansion and contraction.

The excavation for the lower levels of the arcade and the underground practice rooms, however, was more daring since it involved significant underpinning of the original load-bearing brick walls. Says Elefante, "By the time you hit the foundation, the walls are four feet thick." The structural engineer designed the underpinning and reviewed every submittal very carefully to ensure that the contractor was proceeding according to a very methodical process, building one pier at a time. And extremely sensitive monitoring devices were placed at the underpinning locations to keep close tabs on how much the historic structure was settling due to the work.

More than anything else, the Conservatory desperately wanted a well-designed rehearsal room for its orchestra. At the same time, given the tight site and historic nature of the building, this was the most difficult problem to solve. The Institute, in consultation with Acoustic Dimensions of New Rochelle, New York, was determined to convert East Hall-- the original lecture room in the Library Building-into such a space before Quinn Evans was retained. It was up to the architecture firm, however, to make this a reality.

The hall was designed with tiered platform seating and a speaker's dais. When the architects arrived, the space was being used as a makeshift music classroom and library storage space. Ten brick arches spanned visible brick pillars, which clearly presented sightline challenges for the intended function. On closer inspection, however, the architects discovered a single, slender cast-iron column hidden within the storage area. Archival research and limited destructive testing revealed that the other pillars were indeed brick casings around the same cast-iron element. It was a "yahoo" moment for the architects, recalls Elefante, who were relieved to know the removal of these bulky outer shells would be in keeping with their preservation goals.

Alas, their structural work was not over. These very slender cast-iron columns, which held up the six floors of stacks above, were built in 1875. According to Elefante, structural engineering guidelines were revised after that date to add a necessary factor of safety. In addition, analysis of the slenderness ratio for these columns indicated that, by today's standards, they were too thin for their height. To resolve these structural problems, steel pipes were run from the middle of the columns to each other and to the exterior masonry wall. For fire protection, the columns were completely encapsulated with a cast plaster housing that echoes the cast-iron style. The new horizontal bracing was finished with intumescent paint, a special coating that, when exposed to heat, expands into a fire-rated foam.

The renovated hall features "box-in-box construction" so that the inner performance space remains acoustically separate from the rest of the building by preventing sound energy from passing between the inner structure of the hall and the outer structure of the building. Drywall is installed on framing suspended by spring isolation hangers from the slab above. Framing for the double-height walls are supported by sway braces, which are often used in seismic construction and consist of two "u"-shaped interlocking forms separated by a neoprene pad. And the floor slab is poured on a deck that floats over hundreds of one-foot-on-center neoprene pucks.