Cambridge, MA

Ragon Institute


The Ragon Institute studies the human body’s immune system and diseases affecting it. The institute was relocating their headquarters to a new building in Cambridge, Massachusetts. The plans for the new building included a monumental stair in the atrium that would connect Levels 2 to 5. SGH provided delegated structural design services for the stair to the stair fabricator.

SGH evaluated the proposed design and provided a final design for the stair, which is triangular in plan and forms a single-helix shape with its plate stringers. Each run between levels is constructed with three connected segments. Highlights of our work include:

  • Analyzing the column-free stair structure, its connections to each floor, and its cantilever behavior into the atrium space
  • Confirming the proposed dimensions for the steel sections would meet the strength requirements
  • Assessing the stair’s vibration performance, considering the long base building spans between columns and the lightly framed composite-steel deck
  • Designing connections from the stair to the base building to help the structure meet vibration requirements and forcing the stair to oscillate with the floor slabs

We also collaborated with the specialty fabricator to develop a frame that could be erected segmentally, allowing them to temporarily support the segments during construction until the completed structure was in place and connected to the building.

Project Summary



Completion Date
New Construction
DeAngelis Ironworks

Key team members

Paul Kassabian
Paul Kassabian