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The traditional form of grooved rail is the girder guard section illustrated to the left. This rail is a modified form of flanged rail and requires a special mounting for weight transfer and gauge stabilisation. If the weight is carried by the roadway subsurface, steel ties are needed at regular intervals to maintain the gauge.
The wheel flange presses against the side of the curved rail [citation needed] so the "contact point" between rail and wheel moves a few millimeters outwards, making the effective diameter of the outer wheel temporarily larger, and equally opposite: the effective diameter of the inner wheel effectively becomes temporarily smaller.
The Nadal formula assumes the wheel remains perpendicular to the rail—it does not take into account hunting oscillation of the wheelset, or the movement of the wheel flange contact point against the rail. [3] A variation of the Nadal formula, which does take these factors into consideration, is the Wagner formula.
Grooved rail, used when track is laid in places traversed by other vehicles or pedestrians. A grooved rail, groove rail, or girder rail is a special rail with a groove designed for tramway or railway track in pavement or grassed surfaces (grassed track or track in a lawn). The head on the right-hand side of the rail bears the vehicle's weight.
In the 1830s rolled T-shaped (or single-flanged T parallel rail) and I-shaped (or double-flanged T parallel or bullhead) rails were introduced; both required cast-iron chairs to support them. [36] Originally, iron keys were used to wedge the rail into the vertical parallel jaws of the chair; these were superseded by entirely wooden keys. [36]
Cast iron rails, 4 feet (1.2 m) long, began to be used in the 1790s and by 1820, 15-foot-long (4.6 m) wrought iron rails were in use. The first steel rails were made in 1857 and standard rail lengths increased over time from 30 to 60 feet (9.1–18.3 m). Rails were typically specified by units of weight per linear length and these also increased.
Most countries use one of the rails as the reference rail. For example, North America uses the reference rail as the line rail which is the east rail of tangent track running north and south, the north rail of tangent track running east and west, the outer rail (the rail that is further away from the center) on curves, or the outside rails in ...
Generally the aim is for trains to run without flange contact, which also depends on the tire profile of the wheels. Allowance has to be made for the different speeds of trains. Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail.