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