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

249. There are three general forms which may be given to the intrados of a stone arch.

Semicircular, or one hundred and eighty degrees.

Segmental, less than one hundred and eighty degrees.

Basket handle, nearly elliptical, being formed by a number of circular curves.

Full centre (semicircular) arches offer the advantages of great solidity and ease of construction; but unless the springing lines are high, contract considerably the water-way.

Segmental arches give the freest passage to the water, are easily built, but throw a great horizontal strain upon the abutments.

The basket handle gives free passage to the water, when not too flat are very strong, are easily adjustable to different ratios between the span and the distance between grade and the spring line, and except making the centres, are easily built. Whatever the form of the arch, the line of arch springing should not be below high water.

The manner of tracing the full centre and segmental curves is too simple to need remark.

250. In tracing the basket handle curve, the following conditions must be observed:—

The tangents at springing must be vertical.