Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

CLASSIFICATION OF IRON BRIDGES.

220. Iron bridges may be classified as follows:—

Those entirely of cast-iron, or Arch and Girder bridge.

Those of wrought iron alone, or Tubular and Girder.

Those of iron wire, or Suspension bridges.

Those of cast and wrought iron, or Trussed bridges.

The order in which these bridges may be placed as regards cost of construction, and extent of application, is as follows:—

Number.	Span.		Description of bridge.
1	10 to	50 feet	Cast-iron girder.
2	50 to	200 feet	Cast and wrought combinations.
3	200 to	2000 feet	Suspension.
4	200 to	500 feet	Cast arch.
5	25 to	100 feet	Boiler plate girder.
6	100 to	500 feet	Tubular.

Numbers 2, 3, and 5, are the forms which are in use upon American roads. No. 1, is very liable to failure, requires much more knowledge and care in building, and is far more expensive than a wooden truss, or trussed girder. No. 4, is very expensive, and causes a greater obstruction to the water-way than any other. The enormous expense of No. 6, should, and will prevent its adoption in the United States. Let us look at the principles of construction of numbers 2, 3, and 5.