REQUIREMENTS OF AN IDEAL RAIL SECTION:
The requirements of an ideal rail section are as follows:
- The rail should have the most economical section consistent with strength, stiffness, and durability.
- The center of gravity of the rail section should preferably be very close to the mid-height of the rail so that the maximum tensile and compressive stresses are equal.
- A rail primarily consists of a head, a web, and a foot, and there should be an economical and balanced distribution of metal in its various components so that each of them can fulfill its requirements properly.
The requirements, as well as the main considerations, for the design of these rail components, are as follows:
The head of the rail should have adequate depth to allow for vertical wear. The railhead should also be sufficiently wide so that not only is a wider running surface available, but also the rail has the desired lateral stiffness. Web The web should be sufficiently thick so as to withstand the stresses arising due to the loads bore by it, after allowing for normal corrosion.
The foot should be of sufficient thickness to be able to withstand vertical and horizontal forces after allowing for loss due to corrosion. The foot should be wide enough for stability against overturning. The design of the foot should be such that it can be economically and efficiently rolled.
These must ensure proper transmission of loads from the rails to the fish plates. The fishing angles should be such that the tightening of the plate does not produce any excessive stress on the web of the rail.
The height of the rail:
The height should be adequate so that the rail has sufficient vertical stiffness and strength as a beam.
The weight of rails:
Though the weights of a rail and its section depend upon various considerations, the heaviest axle load that the rail has to carry is the most important role. The following is the thumb rule for calculating the maximum axle load with relation to the rail section:
Maximum axle load = 560 x sectional weight of rail in Ibs per yard or kg per meter
• For rails of 90 Ibs per yard,
Maximum axle load = 560 x 90 Ibs = 50,400 Ibs or 22.5 tonnes
- For rails of 52 kg per m, Maximum axle load = 560 x 52 kg = 29.12 tonnes
- For rail of 60 kg per m, Max. Axle load for 60 kg/m rail = 560 x 60 kg = 33.60 tonnes
Length of rails:
Theoretically, the longer is the rail, the lesser would be the number of joints and fittings required and the lesser the cost of construction and maintenance. Longer rails are economical and provide smooth and comfortable rides. The length of a rail is, however, restricted due to the following factors:
- Lack of facilities for transport of longer rails, particularly on curves
- Difficulties in manufacturing very long rails
- Difficulties in acquiring bigger expansion joints for long rails
- Heavy internal thermal stresses on long rails.
Taking the above factors into consideration, Indian Railways has standardized a rail length of 13 m (previously 42 ft) for broad gauge and 12 m (previously 39 ft) for MG and NG tracks. Indian Railways is also planning to use 39 m, and even longer rails in its track system. Now 65 m/78 m long rails are being produced at SAIL, Bhilai and it is planned to manufacture 130 m long rails.