Located in Washington, DC’s southwest quadrant across from the National Mall and Smithsonian Museums, L’Enfant Plaza is a massive mixed-use, commercial complex of multiple mid-century buildings originally constructed in the 1960’s. The complex features office/commercial and governmental buildings, a hotel, an underground shopping mall and parking, as well as a major subway station. The overall complex has been undergoing an extensive renovation and redesign, including the redevelopment of the retail mall as well as the existing L’Enfant Plaza hotel and an office building. A new 600,000 sf office building will also be constructed in the center of the plaza.
The retail renovation projects included modernization of the existing underground retail mall, the development of a new glass atrium providing access to the underground retail corridor, and structural strengthening at the promenade and plaza levels to accommodate the future nine-story office building. The strengthening work for the office building was conducted concurrently with the retail renovation to allow retail operations to continue uninterrupted during construction.
For the strengthening portion of the project, a cost-effective demolition concept was devised involving almost no re-shoring of the existing slab. New concrete framing was constructed over an existing auditorium occupied by the National Transportation Safety Board (NTSB). To construct the framing, SK&A assisted the contractor in developing a steel formwork system using new and existing columns for support. A grid of compression beams was also designed to support the plaza layout and future office building concept.
The large glass atrium portion of the project is composed of a series of steel moment frames. Slip-critical bolts at the column-to-beam connection were used to accommodate the contractor’s preference for steel erection. Additionally, the east stair spans between the promenade and plaza levels, with no posts beneath the landings.
The East and West portions of the renovation were designed and constructed as two separate projects. The West project received an SEA-MW award in the $15-40 Million Renovation category in February 2015.