Silman, A TYLin Company, provided structural engineering services for a new addition for St. Luke’s School in New York, New York.
This K-8 school wanted to nearly double the space of its 1950s building to accommodate a growing student population. As is common in Manhattan, the only strategy for significantly expanding the two-story, 27,000-square-foot steel structure was to build up.
Working with architect ABA Studio, Silman designed the two-story addition as a completely independent structure supported on super columns. This avoided a costly seismic retrofit of the existing structure and reduced the impact of the construction on the existing building below.
The eight 40-foot-tall super columns supporting the new addition are threaded through the existing structure to new independent foundations. Four of the super columns are set back up to 30 feet from the face of the building and supported on 170-ton steel caissons. The other four are supported on shallow spread footings. The project team also modified existing framing to insert a new elevator and stair core.
Double-height steel trusses at longest cantilevers and spans of the additions help the building meet load and deflection criteria. The trusses are supported on custom built-up steel girders cantilevering over the super columns below. Silman designed custom shapes to keep the girders shallow enough to fit between the new structure and the existing roof.
Silman coordinated the foundation design with the Port Authority of New York and New Jersey (PANYNJ), the agency that owns and operates the PATH train tunnel that runs beneath the northwest corner of the site. To isolate the new structure from vibrations due to passing trains, Silman detailed the column bases to include two-inch-thick isolation pads, with isolation material between all steel and concrete foundation elements.
- The new addition was constructed without any lost school days or student displacement.
- The school now contains a larger gymnasium, new classrooms and support spaces, and a future outdoor roof play space.