manufacturer, and the month and year of manufacture. Additional markings make it possible to
tell from which heat and even from which ingot the rail came. This information is valuable
because such rail failures as breaks and cracks can usually be traced to an imperfection in the
molecular structure of the steel. If rails from a particular heat continually fail, all from that heat
are removed.
A rail section in the United States is generally 39 feet long. Longer sections are advisable
because they make fewer joints, and faulty joints cause most of the work in track maintenance.
Section I. Crossties
3.12.
GENERAL
Rails must be adequately braced and supported and be subject to a minimum of lateral,
or transverse, stress. The support supplied must be neither rigid nor too yielding: uniform
elasticity throughout is preferred. The railroads rely on crossties to provide the needed bracing
and support, reduce lateral stress, and provide the elasticity of support desired.
Wood is used for ties more often than any other material, although steel and concrete
have been used to a limited extent, mostly in Europe where timber is scarce and expensive.
Wood is preferred because it has a tremendous resistance to impact loads, is usually easy to
obtain especially in the United States, and provides a base into which inexpensive hook head
(cut) spikes can be driven. The disadvantages in using wood lie in its low resistance to abrasive
and cutting wear, susceptibility to rot from moisture, and cost in areas where it is scarce.
An essential part of the track structure, the crosstie has several important functions. With
the aid of fasteners, it provides a means for holding the rail in proper gage and line; it transmits
train weight from rails to ballast; and it can be moved by adjusting ballast distribution around it,
providing a means of obtaining proper track surface and alinement.
The life of ties in service depends on the kind of material, amount and character of
traffic, climatic conditions, method of preservative treatment used, and amount of tie-protecting
devices (tie armor) used in constructing the track. The remaining paragraphs of the section
discuss wooden and other kinds of ties, tie size and spacing, and wooden tie preservation.
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