Boston, MA

2013 Design Biennial Boston, BSA Space, Helix Stair


Envisioned and developed by Matter Design for the third Design Biennial Boston, Helix is a half-scale, unreinforced, custom-fabricated, concrete spiral staircase. SGH collaborated with Matter Design on material analysis, structural design and detailing, casting and curing, and erection at BSA Space. By combining our materials analysis, laboratory, and structural engineering services, SGH helped Matter Design accomplish this complex installation of unreinforced concrete.

As with their past projects, SGH and Matter Design collaborated to integrate design, analysis, and fabrication of Helix. We developed quality models allowing for a near seamless transition from architectural modeling to structural analysis to fabrication. Our team used the models to rapidly assess concepts and finalize construction details.

From the Matter Design models, SGH created finite element analysis models to evaluate the cantilevered, unreinforced concrete steps as individual pieces and grouped assemblies. We determined that each step could support its own weight and the weight of a few steps above, but each sequentially lower step could not support the increasing weight of the whole assembly above. Working together, SGH and Matter Design developed an adjustable clamping detail to affix each stair to the central threaded rod so that each step primarily supported its own weight. To overcome the installation’s tendency to twist upon itself due to the rotating center of mass along the height, we developed a hidden shear-key that prevented the stairs from sliding across each other.

SGH also consulted on the concrete mix design and fabrication of the steps. In SGH’s laboratory, the design team mixed concrete, formed the steps in molds manufactured by Matter Design, and cured the concrete in SGH’s curing chamber. We then tested sample individual steps and stacked-step assemblies to validate the analytical model.

Project Summary



Completion Date
New Construction
Structures | Advanced Analysis | Applied Science & Research
Culture & Entertainment
Matter Design Studio
Specialized Capabilities
AI & Automation | Physical Testing | Materials Science

Key team members

Matthew Johnson
Matthew Johnson
Structural Engineering Division Head, Chicago