A railroad track is mainly composed of rails, railroad ties (sleepers), fasteners, railway switch, ballast, subgrade. The components of railway track play different roles in providing support for trains. The track structure is built for rolling stock to roll upon safely and smoothly. Both passenger lines and freight lines are beneficial from this convenient fast running track transportation.
The main part of a railroad track is rails. Most modern rails have a profile that shaped like an I-beam vertically symmetric but horizontal asymmetric. To meet the needs of turnout, large bridges, and seamless lines and other structures, non-axisymmetric rails are produced as well.
Railroad rails are made from steels which can be subjected to very high stresses by the trains. To make the rail better withstand the forces from all sides, to ensure the necessary strength conditions, the rails should be fabricated with enough height. Its head and foot should have enough area and height, web and foot should not be too thin. Rails are classified according to rail size and rail weight. In general, the heavier rail supports greater axle loads and higher train speeds.
Function of rails
- Withstand heavy pressure and wear of wheels.
- Lead the rolling stock moving forward.
- Provide the minimum resistance of contact between the rails and wheels.
- Disperse the loads to railway sleeper, ballast and subgrade.
A railway sleeper is also called a railroad tie or crosstie. It is an easily overlooked component of railway tracks. The sleepers not only support the rail but also maintain the position of the rail. Besides, it helps to transmit the huge pressure by rail to the trackbed. It is required to have a certain degree of flexibility and elasticity. It can’t be too hard or too soft. When the train passes by, it can be properly deformed to cushion the pressure. But, it has to be restored as much as possible. In the early days, railroad ties are made of wood while prestressed concrete is more common to see now. Sometimes plastic composite ties are also applied.
Fasteners are used for fixing rails to railway sleepers. It is also a very important component of railway track. Most commonly seen fasteners include spikes, screws, rail anchors, tie plates, chairs, etc. Various types of fasteners have been used over the years. Other track materials like rail clip, rail clamp, rail pad, rail joints also belong to railway fastening systems.
The main function of the rail fastening system is as follows.
- Effectively guarantee the reliable connection between rail and rail, rail and sleeper. Maintain the continuity and integrity of the rail to the most.
- Prevent the horizontal and vertical movement of the steel rail relative to the sleeper, ensure the normal gauge.
- Fully exert the buffering and vibration reduction performance under the power of the locomotive and vehicle to delay the accumulation of residual deformation of the line.
Rail clip is used to fix the railroad track to underlying baseplate and sleepers. The clamping force by rail clips helps to maintain the gauge and prevent the rail from moving in the vertical and horizontal direction relative to the sleeper. One extensively used type of rail clip is an elastic rail clip made of hot-pressed spring steel. Its energy produced at elastic deformation can alleviate the vibration and shock when trains moving.
The main application of rail clamps is for cranes. For the installation method, they can be divided into bolted rail clamps and welded rail clamps.
Rail pad, or railway rubber pad, is a material available to decrease the vibration transmitted from the rails to the sleeper or subgrade. It is inserted in between the rail and baseplate or sleeper.
Rail joints, usually called fishplate, commonly known as the joint bar, is a component that joint rails end-to-end. According to different applications, rail joints can be divided into bolted rail joints, compromise rail joints and insulated rail joints.
Railway switch is also called turnout. As its name indicates, it is a component for rolling stocks to turn from one track to another. It is usually laid in large numbers at stop stations and marshalling stations. With turnouts, you can give full play to the passing capacity of the line. Even if it is a single-track railway, lay the turnouts and build a section of the fork line that is longer than the length of the train to split the train. Turnouts play an important role in railway lines.
Railway ballast or track ballast refers to crushed stones placed under the railway track. It forms the trackbed for sleepers to lay on. Although some tracks are ballastless, the ballasted track remains a dominant infrastructure of the most railroad tracks.
The function of railway ballast
- Withstand the pressure transmitted by the sleepers and distribute this pressure evenly on the roadbed.
- Fix the position of the sleepers to maintain the correct line and slope of the track.
- Drain the rainwater around and below the sleepers to prevent the subgrade soil from deforming due to moisture.
- Increase the elasticity of the track, so that the rail after being crushed by the train quickly returns to its original correct position.
- Prevent orbital growth of weeds.
Track subgrade is the formation level composed of native materials underneath a railroad track.