From Ore to I-Beam

The steel frame is one of the three technologies that made the skyline (see Steel Frame 1885 in Series C). This reading follows a single beam from the ground to the sky.

Making steel

Iron ore is iron oxide. In a blast furnace, coke (baked coal) strips away the oxygen and limestone carries off impurities as slag, leaving molten pig iron, which a basic oxygen furnace refines into steel. Most structural steel made in the United States today takes another route: electric arc furnaces melt scrap, including old cars and demolished buildings, so the beam in a new tower is largely recycled.

The wide-flange shape

An I-beam puts most of its steel in the top and bottom flanges, where bending stresses are greatest, and just enough in the web to hold them apart. A rolling mill squeezes a red-hot bloom through successive stands until it has that shape. Sizes are named by depth and weight: a W14×90 is roughly 14 inches deep and weighs 90 pounds per foot.

Fabrication and erection

In the fabrication shop, detailers turn the engineer's drawings into shop drawings for every piece. Fitters and welders add connection plates and bolt holes; each piece is marked so the erection crew knows exactly where it goes. On site, the crane operator lifts, connectors guide the piece into place and bolt it, and the raising gang moves on. Bolts are tightened to specified tension; welds are inspected by eye, ultrasound or X-ray.

Programs on this chain

Welding, CNC machining, drafting/CAD, commercial driving, heavy equipment (crane) operation, construction, and the safety training in Series H.