Chapter 1.2 Railway Track Gauge and Train Guidance.pptx

railway engineering

1. DEBRE MARKOS UNIVERSITY INSTITUTE OF TECHNOLOGY SCHOOL OF CIVIL AND WATER RESOURCE ENGINEERING Railway Engineering Biniyam A 2022

2. Track gauge Track Gauge : Definition: Track gauge, G, is the smallest distance between lines perpendicular to the running surface intersecting each rail head profile at point P in a range from to Z_p below the running surface. Z_p is always 14 mm In the situation of new unworn rail head the point P will be at the limit Z_p below the railhead

3. Track gauge Distance between the inner sides of the rails, measured 14 mm below rolling surface

4. Track gauge Different track gauge values (e) Standard (Normal) gauge (e = 1435 mm) ; Major parts of European railways, USA, Canada, Mexico, China use standard gauge. Metric (Narrow) gauge (e = 1000 mm or e = 1067mm); Broad gauge (e = 1524 mm or 1672 mm); Finland, Spain, Russia and countries in the Former Soviet Union, India, etc

5. Track gauge Track gauges around the world

6. Track gauge All track gauges give the same operational possibilities, however the metric gauges don’t give high speed operation Track gauge and loading gauge are parameters that determine rail network compatibility with adjacent networks, present or future, but the economy aspect of track gauge is minimum

7. Track Gauge EN 13848-1:2003+A1:2008: Track Gauge In the situation of used worn rail head the point P for the left rail can be different from the right rail.

8. Track gauge The theoretical track gauge can be varied due to: Rail wear Rail head deformation Rail roll (rail tilt) Loose fastening Rail buckling EN standards allow for some deviation of the track gauge from the theoretical value – track gauge tolerances Track gauge tolerances are limited in turnouts

9. Track gauge widening National standards may require gauge widening in small radius curves EN (UIC) standard: 10 mm for curve radius 150-199 m 15 mm for curve radius 120-149 m 20 mm for curve radius < 120 m Gauge widening application depends on the type of sleeper and the track form Gauge narrowing (tightening) has very small tolerance -5 mm (gauge value 1430 mm) … safety risk

10. Track gauge widening The designed gauge should change linearly Full gauge widening should be provided for the whole circular curve with the small radius The gauge transition (1 mm per meter) must be placed on the adjacent horizontal element (straight track, circular curve with larger radius, or – ideally – a transition curve) Gauge widening should be avoided in turnouts. Hence, no turnouts within 10-15 metres from a small radius curve

11. Track gauge Measurement technique Manual measurement method unloaded track Using Track recording car - loaded track (Roger 1000 – 15 tonnes axle load) Consequences of track gauge variations: Gauge too wide  derailment Gauge too narrow  flange climbing (derailment) Varying gauge  poor lateral stability Gauge too wide and reverse curves  buffer locking

12. Wheel-rail contact mechanics

13. Wheelset definitions

14. Region A : w heel trea d -rail head contact most common contact region lower contact stress Region B: wheel flange-rail gauge corner much smaller contact area and more severe higher contact stresses and wear rates Region C: wheel and rail field sides contact Least likely contact region High contact stress Undesirable wear lead to incorrect steering of wheelset Wheel-rail contact regions

15. Phenomena in the wheel-rail interface High vertical, lateral and longitudinal contact forces, induce stresses that may cause material yielding and fatigue R olling contact forces combined with friction induce wear Traction and braking lead to wheel sliding leading to rail burns and wheel flats thermal cracks

16. Phenomena in the wheel-rail interface These phenomena may cause irregularities poor vehicle dynamics further increase in contact forces increase in vibration and noise Consequences discomfort for passengers disturbance for the surrounding increased maintenance cost for wheel and rails and other components in a sever case to derailment induced by wheel and rail fracture or by the wheel flange climbing on the rail

17. Basics Concepts The wheels are made conical, the smaller circumference at the outer edge. …if anything throws the wheels in the slightest degree to one side the wheel is immediately rolling on a larger circumference than the other and the tendency to roll back is introduced. The carriage is kept always in the middle of the track. A beautiful arrangement. Brunel, 1838 The flanges are a necessary precaution but they ought never to touch the rail and therefore they cannot be said to keep the wheels on the rails. They ought not to come into action except to meet an accidental, lateral force.….

18. Definitions The steering mechanism of the wheelset is due to the equivalent conicity (the rolling radius difference between the left and the right wheels)

19. Motion of a free wheelset y 2b r o -λ.y r o +λ.y An idealised conical wheelset displaced laterally on cylindrical rails r l = r o -λ.y r r = r o +λ.y

20. Perfect Curving For perfect curving: r   y  R  b r   y R  b W he r e r = the radius when the wheelset is central b = half the gauge R = the radius of the curve  = the conicity of wheel tread (inclination) s o: R  y  r b If the flangeway clearance is exceeded then perfect curving cannot occur and flange contact will take place

21. Exa m ple 1. A wheel with straight cones will have a conicity the same as the cone inc l ina t ion ta n 𝜆 = 𝜆 . For the following data find the lateral displacement needed to achieve a perfect radial steering: rolling radius r = 0.5, 𝜆 =0.05 (inclination 1:20), b = 0.75 and R = 500m For a perfect curving R  r   y R  b r   y  R  b y  r b   . 01 5 m  1 5 mm . 5 500 y  r b  R  . 5 . 75 y  15 mm lateral displacement is needed to achieve perfect radial steering

22. Exa m ple 2. The cone inclination is instead 𝜆 =0.25 (inclination 1:4) , find the lateral displacement needed to achieve a perfect radial steering For a perfect curving y  r b R  y  . 5  . 7 5  . 00 3 m  3 mm 0.25 500 Only 3 mm lateral displacement would be sufficient to achieve perfect radial steering  r  2  . 2 5  . 003  r  1 . 5 mm   r  2 y   r 2 y    r  r l  r r A rolling radius difference between the outer and the inner wheel of 1.5 mm needed