the part of a railroad track that consists of the rails, their joints, anticreepers, and supports (ties, slabs, and so on), and the ballast layer.
The track superstructure receives the load stress from the rolling stock and transmits it to the substructure (the earth bed or man-made structures such as bridges and tunnels). Track superstructures also include switches and dead crossings. The ties, which are made of wood, reinforced concrete, and, less frequently, of metal, ensure the fixed relative position of the rails; they receive the pressure from the rails and transmit it to the ballast layer. On certain sections, ties have begun to be replaced by solid-block, reinforced-concrete footings in the form of slabs or bed plates. Anticreepers in the form of metal clamps keep the rails from slipping along the track during the passage of trains.
The track superstructure of subways, streetcar lines, and bridges is distinguished by certain characteristics: in subway tunnels it usually does not have a ballast layer, and the ties are laid on the concrete foundation of the tunnel. Streetcar track superstructure is influenced by the need for convenient crossing of the streetcar tracks by automobiles and for reliable bonding with the road pavement. In connection with these factors, streetcar lines on streets that have heavy automobile traffic customarily use grooved rails mounted on a solid reinforced-concrete foundation with ties set into it or on a foundation of concrete slabs with a layer of ballast between the slabs and the ties. In many cases, track superstructure on bridges is laid without a ballast layer. In such cases the bridge beams are used instead of ties.
The type of track superstructure (the kind of material and the dimensions of the components) depends upon the freight-traffic density. For railroad trunk lines in the USSR the following three types are utilized: I—extra-heavy, for an annual freight-traffic density exceeding 50 million ton-km per km and rails weighing 75 kg per linear m; II— heavy, for a freight-traffic density of 25-50 million ton-km and rails weighing 65 kg; and III—normal, for a freight-traffic density of up to 25 million ton-km and rails weighing 50 kg.
As of 1970, work was being carried out in using solid reinforced-concrete footings under the rails.
REFERENCESShakhuniants, G. M. Zheleznodorozhnyi put’. Moscow, 1961.
Chernyshev, M. A. Ustroistvo, soderzhanie i remont puti, 2nd ed. Moscow, 1963.
K. M. DOBROSEL’SKII and V. I. TIKHOMIROV