Thornton Tomasetti provided structural design for a 1.4-million-square-foot mixed-use development at Washington’s Square 54 that includes a 10-story, LEED Gold certified office building, two residential towers, retail, below-grade parking that extends five levels beneath each building, and a central courtyard above a loading dock.
The office component comprises two cast-in-place, post-tensioned concrete structures, tied together with one-way slabs at levels three through 10. To speed construction, they were built simultaneously by different crews, then joined. A two-story atrium, custom-designed by Thornton Tomasetti, consists of two structural glass walls that connect the structures at ground level. Stainless steel tension rods and point-supported, locally edge-clamped, mullion-free glass provides a clear view from street to courtyard. The integrated canopies and inner façade walls make innovative use of glazing panels as primary load-carrying structural members.
The 12-story residential component includes 335 apartments of varying size and floor plan, a fitness center, and an extensive rooftop plaza that features a pool as well as green roof areas.
The project’s configuration posed a series of challenges. Integration of multiple structures on a sloping site required highly coordinated structural design. A shared loading dock is situated beneath a central courtyard with trees and a fountain. The courtyard is supported on upturned steel beams that span over 60 feet to provide a column-free area for the loading dock below and double as framing for planting-bed walls. The structural design for each of the four building structures includes significant shifts in column locations to reconcile an efficient parking garage grid with the above-grade office or residential floor-plate needs. Many sloping columns, transfer girders, and corbels were required to achieve this column-grid optimization.
Project Stats
Location: Washington, D.C.
Owner: Boston Properties
Architect: Pelli Clarke Pelli Architects (Design) & Hickok Cole Architects (Executive)
Area: 1.4 million sf
Completion Date: 2011
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