Superstructure of the track: device and types

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Any railway track is a complex complex of various kinds of engineering structures that form a road with a rail guide track. It consists of two main parts - the lower support and the upper. The latter is actually the road on which the rolling stock runs.

Main purpose

When the train moves, the superstructure of the track receives both vertical and horizontal loads from its wheels and transfers them to an earthen or artificial base. The track itself determines the direction of movement of the train. The VSP is designed, first of all, taking into account the fact that in the future it should ensure the safe passage of trains with specified maximum speeds.

Design Features

The superstructure of the railway track consists of two main parts:

• sleeper rail;
• ballast prism.

The lattice structure, in turn, includes the actual rails themselves, as well as sleepers made from different materials. Upper Path Prismmay be single or double layered. Most often, the latter option is used in the construction of a railway line. A two-layer ballast prism usually consists of:

• sand backing layer;
• rubble made from hard rocks.

For filling a single-layer prism, materials such as sand and gravel, crushed stone, asbestos production waste, slag, shell rock can be used.

In addition to the grating and prism, the following elements of the upper track structure are distinguished:

• bonds;
• anti-theft;
• deaf intersections;
• turnouts.

VSP design

While drawing up the drawings of such an important structure as the superstructure of the track, engineers must solve the following tasks:

• define class, category and path group;
• determine the design of the VSP itself;
• determine the conditions for its installation;

• calculate the increased and decreased temperature of the whips, taking into account their strength and stability;
• calculate lash fixing intervals;
• determine the elevation of the rails and the gauge in the curve.

Superstructure of the railway track: rails

This structural element of the VSP is designed to actually guide the movement of the train. In some cases, the rails may also serve as an electrical conductor.current (in areas with electric traction or auto-blocking). This VSP element can be marked as P50, P65, P75 and P43. Currently, in the construction of railways, the P65 variant is mainly used. Actually the rail itself consists of:

• heads;
• necks;
• soles.

The standard length of rails in the Russian Federation is 25 m. In some sections of the lines, shortened guide elements can also be laid - by 24.84 m and 24.92 m. In order to reduce the number of joints between the rails, they are often welded in whips with a length of 800 m or more.

Materials of track structure: rail fabrication

This VSP element is usually made at the enterprises of the metallurgical industry from open-hearth carbon steel. The rails are carefully heat treated along their entire length by quenching in oil and tempering in a furnace. This procedure is carried out primarily in order to increase the wear resistance of the alloy. Hardened rails last one and a half times longer than untreated ones. Currently, steel elements can be used in the assembly of railway tracks:

• low temperature (P65);
• First group hardened boron vanadium-niobium steel.

The last type of rail is usually used for laying tracks in areas with severe climatic conditions - in the Far East, Siberia, etc.

VSP sleepers

The main purpose of under-rail supports in the track bed is the perception of the load from the rails and their transfer to the ballast prism. The sleepers also ensure the stability of the gauge in plan and profile. In our time, sleepers can be made either from reinforced concrete or from wood. Metal is not used for this purpose due to its susceptibility to corrosion. 80% of the sleepers laid in the country are made of wood. In the production of this VSP element, species such as fir, birch, larch, pine, etc. can be used.

Reinforced concrete sleepers are usually laid only on artificial structures - in tunnels and on bridges. Such supports can be small frames or slabs.

The length of the sleepers depends on the characteristics of the section of the track on which they are laid. Thus, wooden poles have a standard length of 2.75 cm. The permissible deviation from the norm is 2 cm.

The cross section of wooden sleepers can be:

• cut;
• semi-edged;
• unedged.

Reinforced concrete sleepers are made with a section variable along the length. For their production, heavy concrete grade M500 or F200 is used. In this case, the fittings are used from 3 mm wire. Sleepers are laid on the track in the amount of 2000 pieces / km in difficult areas. On straight lines, they are distributed at 1440-1600 pieces per kilometer.

Classificationsleepers

Reinforced concrete track supports, depending on the degree of crack resistance and the accuracy of geometric parameters, are divided into products of the first and second grade. The device of the track structure in different cases involves the use of wooden sleepers of the following classes:

• First (I) - for the main tracks.
• Second (II) - for stationary and access roads.
• Third (III) - for industrial tracks that are not subject to frequent loads.

Wooden sleepers last 12-15 years without the need for replacement, reinforced concrete sleepers - up to 50 years. The disadvantages of the latter, however, are considered to be their heavy weight and high degree of electrical conductivity.

VSP ballast layer

The purpose of this VSP element is to transfer the load from the rails and sleepers directly to the layers of such a base as a subgrade (upper). The structure of the upper path on bridges is slightly different. The ballast prism in this case is not equipped. On earthen plots, it is most often made from crushed stone of hard rocks. Sand and gravel ballasts, since they do not drain water well, are equipped only on unimportant lines. In heavily clogged areas, in most cases, an asbestos substrate is poured and rammed. During rain, a not too thick crust forms on it. The latter serves as a good obstacle to the penetration of various kinds of weeds into the ballast.

VSP turnouts

The structural elements of the superstructure of this type of track can serve to ensure the movement of trains from one trackto another or to rotate the carriage 180 degrees. They are also used when crossing paths in the same level. The main elements of a railroad switch are:

• actual arrow with a transfer mechanism;
• cross;
• connecting paths;
• transfer bars.

Main types of VSP

Currently, the following types of superstructures are used on the main roads of the Russian Federation:

• heavy;
• medium;
• light.

The VSP class is determined depending on its gross traffic density. This is explained primarily by the fact that, unlike most other engineering structures, all its components work with accumulating residual deformations.

The heavy superstructure of the track implies the use of P75 class rails in most cases. As a basis, a prism of crushed stone or asbestos waste is used. Such structures are intended for highways with a traffic density of 80 million tkm/km per year.

Middle type involves laying P65 rails. It is intended for lines with a traffic density of 25-80 million tkm/km per year. Also, such tracks are being laid for high-speed passenger trains and in sections with especially heavy traffic.

The light type of VSP, in turn, is divided into two main varieties:

• for lines with intensity from 5 to 25 million tkm/km inyear;
• less than 5 million tkm/km per year.

In the first case, P50 rails are used for laying. Also in such areas, old steel guides P75 or P65 can be used. For laying tracks with a tension of 5 million tkm / km per year, used R50 rails are usually used. The VSP light type prism is usually equipped with a gravel-sand mixture.

Seamless rail tracks

In areas with reliable soil, it is recommended to equip this particular type of VSP. In Russia, the length of the lashes of seamless tracks is on average 500-600 m. Their undoubted advantages include:

• facilitating such a procedure as the repair of the superstructure of the track;
• increasing the service life of the VSP;
• increasing the smoothness of train traffic.

The seamless path is, in fact, a more advanced design than the conventional one. However, designing it is a somewhat more complicated procedure. Indeed, in this case, additional thermal stresses arise in the rails.