Poetic Descent: The Story of NMAAHC's Iconic Grand Staircase

From our Ideas + Buildings blog

Since 2010, Perkins+Will’s Technical Design Community (TDC) has hosted an annual firmwide competition. At first, the competition rewarded project teams whose contract document sets most closely adhered to the firm’s documentation standards. In 2016, the TDC shifted the competition’s focus to celebrate design innovation in detailing. This year, each of our offices could submit up to two details that best exemplify creativity, innovation, and technical prowess in the face of a challenging design conditions. After three rounds of judging evaluating creativity, level of technical difficulty, cost-consciousness, and elegance of the solution, our team, the North Carolina practice, prevailed to win the 2017 Transcendent Detail Competition.

The monumental spiral stair at the National Museum of African American History and Culture (NMAAHC)* was awarded first prize due to its understated complexity, its minimalist detailing, and its importance to the project’s program. The NMAAHC team faced a significant design constraint: The museum’s program could not fit on the site and within the height restrictions mandated for the National Mall. As a result, a large part of the museum had to be located below grade. However, with all museum visitors arriving at grade level and roughly half the exhibit space below grade, circulation and building navigation play a critical role in the visitor’s experience. Although escalators carry most visitors to the lower level, the monumental stair provides a strong visual and spatial connection between the levels, encouraging visitors to explore the lower-level History Gallery, Cafeteria, Contemplative Court, and Oprah Winfrey Theater. The stair is designed to be an organic sculptural element in an otherwise rectilinear building, connecting the first floor down to the lower level 35 feet below.

The completed stair at the National Museum of African American History and Culture.

The complexity of the detailing begins with the stair’s large scale and unusual geometry. The stair is not a circular helix, but instead an elliptical helix, making it far more difficult to design, document, and build. Each panel of the stair’s underside had to be a dual-curvature hyperbolic paraboloid to maintain the stair’s pure and seemingly simple geometry. Careful coordination of all the stair’s various elements was needed to ensure precise three-dimensional alignment.

To achieve the stair’s 270-degree twist and monumental scale, a custom structural steel box beam was designed to curl with the stair. The beam is attached to the primary building structure only at the upper and lower ends, with no intermediate supports. Controlling vibration of this large span was a critical structural challenge, requiring extensive virtual modeling. To further enhance the minimalist detailing, indirect lighting was integrated into the handrails while sprinkler pipes were threaded inside the cladding; both systems had to navigate through the load-bearing top and bottom floor connections.

An economy of materials contributed to the design aesthetic: oil-rubbed raw steel for the guardrails and underside soffit, cast terrazzo for the treads, and bronze for the handrails. All connections of the stair’s components to the structural box beam were concealed. The joints between materials were designed to allow for structural deflection, while not detracting from the stair’s overall visual impact.

Preparing and reviewing submittals required intense coordination between designers and builders. Several rounds of reviews with the steel subcontractor were needed to ensure the joints on the inside and outside wall panels would align with the joints on the underside of the stair. The steel subcontractor’s shop drawings then served as a base for the handrail, terrazzo, and electrical subcontractors’ shop drawings, each of which had critical alignments to maintain.

In the end, the only visible modification from the original design was the introduction of small weld between the side panels directly behind the handrail. Given that the wall panels cantilever from the steel box beam, the welds helped align the side panels and keep them vertical.

The NMAAHC project team and the North Carolina practice are honored and humbled by this award, which as always involved competing against a wide array of other beautiful and technically challenging details. We look forward to the competition again next year, and will find a place of honor for the trophy when we move into our new office later this summer.

Another view of the stair at the National Museum of African American History and Culture.

* The Freelon Group, Architect of Record of the National Museum of African American History and Culture (NMAAHC), was part of the Freelon Adjaye Bond/SmithGroupJJR collaboration. In 2014, The Freelon Group joined and has become part of Perkins+Will.

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