Stunning Stair

January 9, 2024
Stunning Stair

Careful analysis and thoughtful steel details make this monumental staircase an architectural and serviceability success.

Monumental staircases add a signature element to a building—but also an element of complexity.

Such a scenario can be found in Cambridge, Mass.: the three-story staircase in The Ragon Institute of Mass General, MIT, and Harvard’s soon-to-be-opened 323,000-sq.-ft headquarters. The stair posed several structural challenges, the most prominent being its triangular helix geometry and the base landing on structural steel framing rather than a slab on grade.

The new building will be a collaborative research center that brings together scientists, clinicians, and engineers from diverse fields to harness the immune system to combat and cure human disease. The stair will connect these various disciplines and foster collaboration.

The stair is comprised of three runs from the second to the fifth floor. Its geometry is a single helix that, when viewed from above or below in plan, forms a triangular shape. It is supported at one point of the triangle at each floor level. The interior and exterior stringers are 3/4 in. thick by 5 ft deep ASTM A572 steel plates. The width of the stair is 5 ft, 2 in. Treads and risers are comprised of 3⁄8 in. steel plates supported by HSS4×4×. beams spanning between stringers and will be covered by a terrazzo finish. The stair will support glass guardrails at both stringers.

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