The challenge was significant: A spiral staircase in architectural concrete, with a broad, curved landing three steps up and a larger boat-shaped landing half way to the second floor. Monolithic sidewalls supporting a polished brass handrail end in scrolling curves with a 1-foot radius. With a skylight above and overhanging cast-in-place planter boxes at the upper landing level, the stairway is planned as the dramatic focal point of a new public library. This article details some of the five months of forming and placing operations required for successful completion of the stairs.
BUILDING THE FORMS
Two men worked four months constructing the forms. The formwork had to be finished almost as carefully as cabinet work, and strong and rigid enough to hold the fresh concrete and the men placing it.
The stairway and its sidewalls lie within a 27-foot-diameter circle. The upper landing and planters have their own radiuses as do the lower landing and the scrolling curve with which the sidewalls end. To build all these intersecting curved surfaces, the carpenter foreman decided to start with a full-scale layout which he drew on the steel troweled slab.
SIDEWALLS FOR THE STAIRCASE
The stairs have exposed concrete sidewalls 3 1/2 feet high above the treads, with a formed recess for the polished brass handrail. Form ties used in these 8-inch walls had plastic cones which left 2-inch-deep recesses that became a visual feature of the sandblasted concrete. The walls were to be placed monolithically with the stair soffit in a continuous pour. There were no control joints and no construction joints.