I-Beams (also known as W-beams, for "wide flange", or double-T) are beams with an I- or H-shaped cross-section. The horizontal elements are flanges, while the vertical element is the web.
There are two standard I-beam forms:
Rolled I-beam, formed by hot rolling, cold rolling or extrusion (depending on material).
Plate girder, formed by welding (or occasionally bolting or riveting) plates.
