RAIL CORRUGATION
Corrugation
Rail corrugation is the most common form of periodic damage on rails.
Corrugations can vary in both wavelength and amplitude (corrugation depth)
In most cases, corrugation is caused by wear. Metro and Tram type systems typically suffer from corrugation most.
This is mainly due to the fact that these type of systems (compared to conventional railways) have:
Tighter curves
Higher braking and acceleration rates
Lighter axle loads
Typically rail corrugation can be classified in:
Short wave corrugation
Long wave corrugation
Short Wave and Long Wave Corrugation
Corrugation classified as “short wave” typically relates to waviness in the 10-100mmwavelength range.
Short wave corrugation is wear in the longitudinal profile of rails which can be caused by:
Rail vibrations
Wheel slip in curves
Braking and accelerating of trains
Any rougness which can act as an initiator for vibrations and development of corrugations (e.g. poor welds)
Corrugation classified as “long wave” typically relates to waviness in the 100-300mmwavelength range.
Long wave corrugation is wear in the longitudinal profile of rails which can be caused by:
Low frequency track resonance
Plastic flow of the rail material due to excessive stresses between wheel and rail (e.g. high axle loads, high speeds, high friction, poor wheel rail contact)
Short wave corrugations typically tend to cause for trackside noise nuissance in same cases as much as 10dB
Long wave corrugations typically tend to cause for groundborne noise causing for problems for people living close or above the railway
Common types of corrugation damage mechanisms
RUTTING:
Perhaps the mosts common type of corrugation on metro and tram type systems. Corrugation can be particularly severe on low rails in curves because wear is high due to torsional and/or bending resonances of wheelsets when negotiating relatively sharp curves.
Rutting type corrugation has a short to medium wavelength and often causes for medium frequency noise (50-150Hz)
PINNED-PINNED:
A type of corrugation damage caused by vibrations of rails between the fastenings, rather like a guitar string. Typically these corrugations can be found on tangent tracks or mild curves and are more severe over the sleepers than in between sleepers. The caracteristics of this type of corrugation (wavelength and severity) are a function of track stiffnes, sleeper spacing and train speeds
Pinned-pinned type corrugation has a short wavelength and often causes for high frequency noise (450-1200Hz)
P2 RESONANCE:
A type of corrugation which is common on both metro and tram systems as well as conventional and heavy haul railways. Typically these corrugations can be found on tangent tracks and high rails in curvesand are caused by vehicles “bouncing” on the track. Rather stiff track with variations in rail support lead to low frequency resonance which in turn lead to long wavelength corrugations. These long wave corrugations often lead to a low frequency “rumble”noise often well transmitted into buildings.
P2 type corrugation has a long wavelength and often causes for low frequency noise (50-100Hz)
It is not usual that different types of corrugations occur on the same track, quite often this is found on tram and metro systems
High rail corrugation (long wave)
Long wave corrugation on high rail of curve likely caused by P2 resonance due to stiff track
Low rail corrugation (short wave)
Short wave corrugation on low rail of curve likely caused by rutting resonance due to wheelslip or torsional resonance
Corrugation Frequencies
Most corrugations have a constant frequency where the wavelength can be calculated as follows:
λ= v/f
v = trainspeed
F = frequency of the wavelength fixing mechanism
Pinned-pinned corrugation with a 500Hz resonance frequency would have a wavelength of 40mm where trains would travel at 70km/h (20m/s) as:
20/500 equals 0.04m or 40mm
It is also possible to calculate the estimate noise frequency from trains travelling over corrugated track if train speed and corrugation wavelength are known. If for example the wavelength of the corrugation is 40mm (0.04m) and trains travel at 200km/h (55m/s) than the frequency would be:
0.04 = 55/f
f = 1375Hz
Would that same train run over the same track at 40km/h (11m/s) than the frequency would be:
0.04 = 11/f
F = 275Hz
