STRUCTURAL ENGINEERING FIRM:
Up to 0.15 percent
HIGH-PERFORMANCE CONCRETE SHRINKAGE:
Less than 0.06 percent
The Miles Stair is a 12-foot-wide helix of white concrete that winds through five stories of Somerset House, a cultural center in London. Staircases typically use surrounding walls for support, but the Miles Stair relies on a core built from a latticework of lightweight stainless steel. Engineers managed to pull off this improbable structure because the steps are built from high-performance concrete, which is stronger, lighter and more stable than regular concrete.
Mixed with steel or nylon fibers, high-performance concrete is almost as strong as cast iron. It was invented to fill in gaps in large concrete works such as bridges, but within the past five years, engineers have increasingly used it to built entire structures. It also does not shrink over time like ordinary concrete does, so “what you cast is what you get,” says Matthew Wells, a project representative at Techniker, the London-based firm that built the staircase.
The Miles Stair is a nominee in the Institution of Structural Engineers’ Structural Awards, which recognizes projects for their engineering, elegance and economy. The winner will be announced on November 14, but to Wells, the staircase has already proved itself: there is an elevator at its center, but hardly anyone uses it.