Girder cut from joist.
Rubber I-beam suspended flatwise, and edgewise.
Simple girder contours.
Girder contours simple and built up.
Girder forms in locomotive draw-bars.
Girders of steel are rolled and riveted together at the mills in a variety of contours, each best for a specific duty, as the skeleton of a floor, a column, or a part of a bridge. Their lengths, if desired, may far exceed those possible to wood. Their principal simple forms are the I-beam; T, the tee; L, the angle; C, the channel; and the Z-bar. Of these the I-beam is oftenest used; its two parallel flanges are at the distance apart which practice approves, they are united by a web just stout enough not to be twisted or bent in sustaining its burdens. Crank shafts of engines, to withstand severe strains, are built in girder fashion; so are the side-bars of locomotives and the braces of steel cars. Plates riveted together may serve as compound girders or columns of great strength and rigidity. In the New York subway the riveted steel columns which support the roof have a contour which enlarges at the extremities.