Steel Frame 1885

The Home Insurance Building on the corner of LaSalle and Adams in Chicago was ten stories when it opened in 1885 and twelve after 1890. It was not the tallest building in the world; it was the first in which the walls hung from the frame instead of holding the building up. That is the invention.

Before

A masonry wall carries the floors above it, so it must thicken toward the ground. The Monadnock Building (Burnham & Root, 1891), sixteen stories of load-bearing brick, has walls six feet thick at the base and windows that are slots. The Monadnock is the end of the line for that method: heavier walls eat the ground floor, and the ground floor is the rent.

The idea

William Le Baron Jenney, an engineer trained in Paris, is said to have watched his wife set a heavy book on a birdcage and seen that the cage held. Whatever the story, the principle is the same: a skeleton of iron and steel columns and beams carries every load to the foundation, and the exterior wall becomes a curtain that carries only itself. Floors stack without limit until wind, elevators and money say stop.

The Chicago school

Jenney's office trained Burnham, Sullivan and Holabird; Chicago after the 1871 fire was a laboratory. The Rookery, the Reliance Building with its glass, the Marquette — each pushed the frame further. By 1913 the Woolworth Building in New York reached 792 feet on the same principle.

Steel today

Rolled wide-flange sections, high-strength bolts, welded moment connections, composite floors of steel deck and concrete, and — since the 1960s — the tube (the World Trade Center, the Sears Tower) and the concrete core with steel outriggers (most supertalls). The connections are where towers live or die; that is why the welding and inspection standards (AWS D1.1) are as strict as they are.

The trades

Ironworkers raise and bolt the steel — the connectors walking the beams are the image of the trade. Welders make the moment connections. The crane operator lifts every piece. Inspectors ultrasonically test the welds. The drafting/BIM technician models every beam before it is rolled.

Why it matters here

The steel frame is the technology condition of the vertical push. Land price supplies the reason; the frame supplies the means. Without it, the bid-rent curve would have produced Paris, not Chicago.