Tension Net Stair
Chicago, Illinois
Engineer: Dewhurst Macfarlane & Partners
1993-1995

The Tension Net Stair is the sculptural centre piece and only stair within the two story penthouse apartment of a mixed-use tower in downtown Chicago.  The thin concrete floor slabs could not support the load of additional construction so the staircase is suspended from steel beams below the ceiling slab.  The central tapered and conical tension net of stainless steel rods is stiffened by post-tensioning against the lower floor and a series of integral horizontal compression rings.  The mass of the glass stair treads also helps to stiffen this net.  The delicate woven structure appears as a vortex around which are spun the acid-etched laminated glass treads.
The treads are a three-ply lamination of acid-etched and annealed glass with a total thickness of 1-1/4”.  They are supported along two of their three sides by nylon strips on aluminium bars.  The use of laminated glass achieves a combination of mass (which helps to tension and stiffen the structure) and visual lightness.  The acid-etched surface of each tread acts as a projection screen for the complex shadows of people and the structure itself.

Luke Lowings and James Carpenter (as JCDA) were responsible for design, fabrication and installation of the stair as a private commission.

The Project received a citation in the 1996 Benedictus Award.