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Some important terms

Some important terms. SUPER ELEVATION. The outer edge is raised with respect to the inner edge on curve rail section called super elevation. SUPER ELEVATION = Where , G = Gauge of track ( ft ) V = Design speed of train ( ft /Sec) R = Radius of curvature ( ft )

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Some important terms

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  1. Some important terms

  2. SUPER ELEVATION • The outer edge is raised with respect to the inner edge on curve rail section called super elevation. SUPER ELEVATION = Where, G = Gauge of track (ft) V = Design speed of train (ft/Sec) R = Radius of curvature (ft) g = Acceleration due to gravity (ft/sec2)

  3. Problem Fine the Design speed of railroad on a curve if Super elevation is 0.5ft, Gauge is 5’-6” and Radius of Curve is 3500 ft

  4. Sleeper density The number of railway sleepers required to be placed under the track per rail length is called as its sleepers density. • Sleeper Density is Expressed as “n + x” Where, n = length of rail x = Number of sleepers more than “n”

  5. Normally the Length of one rail section is 40-42ft • Pakistan Railway sleeper density ranges from (n+3) to (n+6)

  6. The sleeper density varies according to following factors • Speed and axle load • Type of rail section • Type and depth of ballast • Bearing area of sleeper on ballast • Nature of formation

  7. Spacing of sleepers • Spacing of sleepers depends upon sleeper density • Generally the spacing of sleepers is kept uniform throughout the length of the rail. • Near the joint, two or three sleepers are spaced closer.

  8. problem • Find out the number of sleepers required for construction of a track 960 m long, adopting the sleeper density as n+6 and the length of rail is 13m.

  9. Track stiffness • Rail is assumed to be beam on an elastic foundation. • Modulus of track elasticity, u (or k) • u= P/∆ • Where u= modulus of track elasticity( lbs/in/in) • P= wheel load per unit length of rail (lbs/in) • ∆= unit of track deflection (in),

  10. Up and down movement (pumping) of track under repetitively applied and released loads is a prime source of track deterioration. • Design of track should keep deflection to a minimum. • Differential movement causes wear of track components. • Modulus is defined: load per unit length of rail required to depress that rail by one unit. (lb/in./in.)

  11. Some of deflection is due to rail and ties 0.06 in. • Ballast deflection (compression) 0.15 in. • Rest is due to subgrade (variable) 0.05 – 0.15 in.

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