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

TIMBERWORK.

284. The timber-work supporting the rails consists either of cross ties of wood, hewn flat on top and bottom, of dimensions from 6 × 7 to 7 × 9, and 2½ or 3 feet longer than gauge; or of longitudinal sawed timbers rectangular in section, placed directly beneath the rail, and giving it a bearing throughout the whole length.

Longitudinal bearings seem to possess no advantage over cross ties, but are subject to some decided disadvantages. In case of removal, two rails at least must be taken up to admit of the replacing a timber; while with cross ties any one may be taken out and replaced without even affecting the immediate passing of a train. A continued bearing is no better than a broken one, as the strength of the timber itself offers very little resistance to the weight of a locomotive. Strength is not to be expected in the timber-work; it is only the elastic medium between the rail and the ground serving to maintain the rail in a proper position. The strength is in the rail. The distance at which to place cross ties depends upon the weight of engines traversing the road, the nature of the ballast, and the strength of the rail; somewhere between two and four feet from centre to centre.

The amount of superficial bearing which the timber-work ought to give per lineal foot of rail, is differently estimated by different engineers.

Upon the 4′ 8½″ gauged roads of America, 1¾ square feet per lineal foot of rail has been allowed.

Several of the English roads give the following:—

Name of road.	Gauge.	Square feet per lineal foot of rail.
London and N. W. Railway,	4′ 8½″	3
Great Western,	7′ 0″	2½
S. and W. of Ireland,	5′ 3″	3⅔
Midland G. W. of Ireland,	5′ 3″	27 12

If ties are made eight inches wide, and eight feet long; we have the following amounts of bearing surface per lineal foot of the rail with different distances of the ties.

Distance C to C of tie.	Superficial feet per lin. foot.
2	2.66
2½	2.13
3	1.78
3½	1.53

Of course the longer the tie is made the greater may be the distance between, provided the rail will bear it. Mr. Peter Barlow, in his report of August, 1835, to the directors of the Liverpool and Manchester Railway, fixes the following dimensions for superstructure.

Distance between insides of ties being
	3′	3′ 9″	4′	5′	6′
Weight in lbs. per yard.	50	59	61	67	79
Depth of rail in inches.	4½	4⅝	4¾	5	55 16

At the time these dimensions were given, however, much less weight was applied to the rails than at the present day. As the bearing is increased, the rail must become heavier and more expensive; but the number and cost of the ties is lessened. The report above referred to, concludes that five feet bearings, involving heavier rails, would cost no more, after the road bed is consolidated, than shorter ones; but that on embankments and soft subsoils, it would be at first somewhat more expensive.

285. The object of the ballast is, first, to transfer the applied load over a large surface; second, to hold the timber-work in place, horizontally; and third, to carry away the rain water from the superstructure; it also furnishes the means of adjusting the timber-work to the proper position. It should be at least one half way up the depth of the tie, and deep enough below the under surface to prevent the timber being forced down by the passing weight. From various observations it appears that there should be one and a half times the depth of the tie of ballast, beneath the under surface; or the whole depth of ballast should be from two to two and one half times the depth of tie.

For ballast, broken stone, gravel, or other dry, durable, and porous material, is suitable.

A perfectly inelastic road bed is not to be desired. Something is necessary to absorb the shocks given by the wheels, and prevent their reaction against the machinery. To supply this amount of elasticity, and to transmit the weight evenly to the ground, is the duty of the ballast and timber-work.

Of late years there has been applied, in England, cast-iron hemispherical bowls, designed to take the place of both tie and chair. Such answers very well when there is no lack of ballast, and where wooden ties are worth from seventy-five cents to one dollar each.