Permenent Way Institution - Glasgow Section - Track Quality Measurement and Inherent Design Standard Deviation

Track Quality Measurement and Inherent Standard Deviation

Constantin CiobanuCeng Mres FPWI MCIHTPrincipal Track Engineer

PWI – Glasgow16/11/2016

IntroductionPeriodic track measurement is required to maintain an effective railway track system – safe and with good vehicle ride quality.

Ride quality – Track Quality Index (TQI) defined based on speed and various classes of lines

Safety – well defined exception (exceedance) levels. Identify the isolated defects and establish intervention and immediate remedial actions

Track MeasurementHistorically, the use of track inspection cars can be traced back to the early 1920’s.The Hallade system determines the bogie reaction to track irregularities using a complex mechanical system.

Track MeasurementThe inertial track measuring system was developed in 1960-1970. Non-contact optical sensors + accelerometers are used to measure the track.

Track Safety. Track defects

Track Quality Index

Track Quality Indexes used by the European Railway Networks:

-The number of isolated defects over a specific length (1km) - a very simple way of evaluating the track quality; still used by several European Railway Networks.

-Parameters defined through the Vehicle Response Analysis (VRA) - either a directly measured parameter or the product of a mathematical model that quantifies the vehicle response to the track irregularities. Ex: Vampire Railway Dynamics simulation.

-Power Spectral Density (PSD) – evaluates the energy of the measured signal in relation to its frequency for a given track parameter.

-Standard Deviation (SD) - calculated for each specific wavelength range over a defined length, typically 200m. There is a direct relationship between Standard Deviation (SD) and the Power Spectral Density (PSD).

-Combination of various parameters. The TQI can be expressed as a combined standard deviation (CoSD) computed based on the different set of SD considered in the measurement of track quality (for alignment, cant, gauge, cross level, longitudinal level).

(BS EN 13848. Railway applications - Track - Track geometry quality)

Signal Processing. Fourier Analysis. Standard Deviation

Two (three) wave length bands:• 35m = 1m to 35m (H) and 0.5m to 35m (V)(general track quality index)• 70m = 1m to 70m (H) and 0.5m to 70m (V)(comfort quality index for passenger trains at higher speed – V≥80mph)• 200m = 1m to 200m (H) and 0.5m to 200m (V)(High Speed track quality index V>250km/h – EN13848)

…

…

Fourier analysis - signal simplification

Signal Processing. Fourier Analysis. Standard Deviation

SD1 = 0.5 mmSD2 = 1.0 mmSD=√∑𝑖=1

n

(x i− xm )2

n−1

Two sets of SD values:AL – horizontal alignmentTOP – top of rail - vertical alignment and cant

WT35 – worst of the two tops (left rail and right rail).MT70 – mean top vertical variation (middle track vertical variation)

The SD is a numerical expression the track riding quality on the next 200 m from the reference point (mileage) for which it was computed.

INHERENT DESIGN STANDARD DEVIATION

The design alignment is characterised by Inherent Standard Deviations, affecting the target standard values for construction.

The Inherent Design Standard Deviation is proportional to the additional vehicle acceleration induced by the track irregularities.

g – gravitational accelerationac – centrifugal acceleration

In 2007-08 Network Rail worked with specialist suppliers to develop and prove an “Alignment Design Standard Deviation Calculator” which was calibrated against the output from the track recording software to validate its accuracy.


Inherent Design Irregularities

The design alignment is characterised by Inherent Standard Deviations and these are affecting the target standard values for construction.

The Standard Deviation is proportional to the additional vehicle acceleration induced by the track irregularities.

The following track alignment elements are not causing any additional vehicle acceleration and, consequently, no inherent standard deviations:• Straight horizontal element• Circular horizontal arc• Constant cant element• Straight vertical element

At the points where there are changes to these geometrical elements, vehicle accelerations and inherent design standard deviations are generated.

Any change in the vehicle lateral or vertical acceleration due to the design, is a source of oscillations:

- Horizontal transition (AL35 and AL70)

- Cant transition (WT35 and MT70)

- Gradient change (WT35 and MT70)

- Vertical curve (WT35 and MT70)

Inherent Track geometry Standard Deviation

(SD present in the design and not caused by installation)

Inherent Track Quality Standard Deviation

SD

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TRK2102 - Installation SD

Band 1 Band 2

Quality Speed AL35 WT35 AL70 MT70 AL35 WT35 AL70 MT70

Q1 10 1.7 2

1.8 2.6

Q1 15 1.7 2 1.8 2.6

Q1 20 1.7 2 1.8 2.6

Q2 25 1.7 2 1.8 2.6

Q2 30 1.7 2 1.8 2.6

Q3 35 1.7 2 1.8 2.6

Q3 40 1.7 2 1.8 2.6

Q4 45 1.7 2 1.8 2.6

Q4 50 1.7 2 1.8 2.6

Q5 55 1.3 1.7 1.4 2.1

Q5 60 1.3 1.7 1.4 2.1

Q6 65 1.3 1.7 1.4 2.1

Q6 70 1.3 1.7 1.4 2.1

Q7 75 1.1 1.4 1.2 1.6

Q7 80 1.1 1.4 1.7 2.1 1.2 1.6 1.9 2.4

Q8 85 1.1 1.4 1.7 2.1 1.2 1.6 1.9 2.4

Q8 90 1.1 1.4 1.7 2.1 1.2 1.6 1.9 2.4

Q8 95 1.1 1.4 1.7 2.1 1.2 1.6 1.9 2.4

Q9 100 0.9 1.3 1.6 2 1 1.4 1.7 2.1

Q9 105 0.9 1.3 1.6 2 1 1.4 1.7 2.1

Q9 110 0.9 1.3 1.6 2 1 1.4 1.7 2.1

Q10 115 0.8 1.3 1.5 1.8 1 1.4 1.6 2

Q10 120 0.8 1.3 1.5 1.8 1 1.4 1.6 2

Q10 125 0.8 1.3 1.5 1.8 1 1.4 1.6 2

Q11 130 0.7 1 1.1 1.3 0.9 1.1 1.2 1.5

Q11 135 0.7 1 1.1 1.3 0.9 1.1 1.2 1.5

Q11 140 0.7 1 1.1 1.3 0.9 1.1 1.2 1.5

Inherent Design SD (TRK001 Mod 11 - TRK2102)

Band 1 Band 2

Quality Speed AL35 WT35 AL70 MT70 AL35 WT35 AL70 MT70

Q1 10 1.3 3.2

1.2 2.6

Q1 15 1.3 3.2 1.2 2.6

Q1 20 1.3 3.2 1.2 2.6

Q2 25 1 2.3 0.9 1.7

Q2 30 1 2.3 0.9 1.7

Q3 35 0.8 2.1 0.7 1.5

Q3 40 0.8 2.1 0.7 1.5

Q4 45 0.5 1.8 0.4 1.2

Q4 50 0.5 1.8 0.4 1.2

Q5 55 0.7 1.8 0.6 1.4

Q5 60 0.7 1.8 0.6 1.4

Q6 65 0.4 1.3 0.3 0.9

Q6 70 0.4 1.3 0.3 0.9

Q7 75 0.4 1.3 0.3 1.1

Q7 80 0.4 1.3 1.3 1.6 0.3 1.1 1.1 1.3

Q8 85 0.2 0.8 0.9 1.2 0.1 0.6 0.7 0.9

Q8 90 0.2 0.8 0.9 1.2 0.1 0.6 0.7 0.9

Q8 95 0.2 0.8 0.9 1.2 0.1 0.6 0.7 0.9

Q9 100 0.2 0.6 0.6 0.9 0.1 0.5 0.5 0.8

Q9 105 0.2 0.6 0.6 0.9 0.1 0.5 0.5 0.8

Q9 110 0.2 0.6 0.6 0.9 0.1 0.5 0.5 0.8

Q10 115 0.2 0.4 0.3 0.6 0 0.3 0.2 0.4

Q10 120 0.2 0.4 0.3 0.6 0 0.3 0.2 0.4

Q10 125 0.2 0.4 0.3 0.6 0 0.3 0.2 0.4

"Good" SD - maintenance

TRK001 Mod11

Speed AL35 WT35 AL70 MT70

10 3 5.2

15 3 5.2

20 3 5.2

25 2.7 4.3

30 2.7 4.3

35 2.5 4.1

40 2.5 4.1

45 2.2 3.8

50 2.2 3.8

55 2 3.5

60 2 3.5

65 1.7 3

70 1.7 3

75 1.5 2.7 3 3.7

80 1.5 2.7 3 3.7

85 1.3 2.2 2.6 3.3

90 1.3 2.2 2.6 3.3

95 1.3 2.2 2.6 3.3

100 1.1 1.9 2.2 2.9

105 1.1 1.9 2.2 2.9

110 1.1 1.9 2.2 2.9

115 1 1.7 1.8 2.4

120 1 1.7 1.8 2.4

125 1 1.7 1.8 2.4

Table A.37 - NR/L2/TRK/2102 - The design alignment standard deviation value when added to the appropriate value above shall not exceed the equivalent value for ‘Good’ track quality in NR/L2/TRK/001.

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Inherent Design SD (TRK001 Mod 11 - TRK2102)Band 1 Band 2

Quality Speed AL35 WT35 AL70 MT70 AL35 WT35 AL70 MT70Q1 10 1.3 3.2

1.2 2.6

Q1 15 1.3 3.2 1.2 2.6Q1 20 1.3 3.2 1.2 2.6Q2 25 1 2.3 0.9 1.7Q2 30 1 2.3 0.9 1.7Q3 35 0.8 2.1 0.7 1.5Q3 40 0.8 2.1 0.7 1.5Q4 45 0.5 1.8 0.4 1.2Q4 50 0.5 1.8 0.4 1.2Q5 55 0.7 1.8 0.6 1.4Q5 60 0.7 1.8 0.6 1.4Q6 65 0.4 1.3 0.3 0.9Q6 70 0.4 1.3 0.3 0.9Q7 75 0.4 1.3 0.3 1.1Q7 80 0.4 1.3 1.3 1.6 0.3 1.1 1.1 1.3Q8 85 0.2 0.8 0.9 1.2 0.1 0.6 0.7 0.9Q8 90 0.2 0.8 0.9 1.2 0.1 0.6 0.7 0.9Q8 95 0.2 0.8 0.9 1.2 0.1 0.6 0.7 0.9Q9 100 0.2 0.6 0.6 0.9 0.1 0.5 0.5 0.8Q9 105 0.2 0.6 0.6 0.9 0.1 0.5 0.5 0.8Q9 110 0.2 0.6 0.6 0.9 0.1 0.5 0.5 0.8

Q10 115 0.2 0.4 0.3 0.6 0 0.3 0.2 0.4Q10 120 0.2 0.4 0.3 0.6 0 0.3 0.2 0.4Q10 125 0.2 0.4 0.3 0.6 0 0.3 0.2 0.4

The TGSD Calculator computes only the Geometrical Inherent Design Standard Deviations.

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Additional design elements (excitators) which will cause vehicle accelerations even for an ideal track:

• switches (or adjustment switches)


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• switches (or adjustment switches)• crossings


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= Inherent Design Irregularities

• joints• welds (No! presumed installed without any irregularity)

• changes in rail inclination (NR V56)• changes in rail head profile• changes in track stiffness

• ballasted to slab track • embankment to bridge • different rail fastenings• …

• use of sleepers ! = discontinuous rail support

Each Inherent Design Irregularity can cause real track irregularities!


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Rolling Standard Deviation

Rolling SD – a graph of the track quality standard deviation. This provides a better image of the track quality.

Expressing the TQ SD only in 1/8 mile points does not always provide a good information on the “disturbance” cause and location.

The SDs tend to increase significantly 200 m before a point of disturbance and to decrease significantly after passing this point.


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1.164 1.223 0.021

The Rolling SD graph shows an increase 200 m before the irregularity and a peak value where the irregularity actually is.


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How can we improve the design inherent quality?• Wherever practically possible, use transition instead of sudden change in curvature (VT) and vertical curve

instead of PVI

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How can we improve the design inherent quality?• Avoid overlapping (of the SD effects for) changes in design geometry:

• Horizontal or cant transition / vertical curve or PVI• Sudden change in curvature (virtual transition) / vertical curve or PVI

• Use long design elements – not the minimum allowed by the design standard

• Avoid changes of track superstructure (e.g. type of rail, fastening, rail inclination, expansion joints, slab/ballasted track) or infrastructure (e.g. formation treatment, stiffness variation). Avoid overlapping them with geometrical changes

• Place S&Cs over constant curvature, cant and gradient

Case study. Cant design over a reverse curve

• Balancing the curvature variation – proportional transition lengths• Balancing the cant / rate of change of cant• Balancing the cant gradient• Balancing the deficiency / rate of change of cant deficiency• What else?








How can we improve the design inherent quality?

• (non-standard) When applying cant, rotate the track around the centreline (see TRK2049 – Reverse curve).

A solution used on the Shinkansen and other High Speed lines. Tram and light rail tracks are usually designed in this way.

• (non-standard) Use non-linear horizontal and cant transitions.

Shinkansen HS – Japanese (cosinusoidal) transition

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Engineering

Permenent Way Institution - Glasgow Section - Track Quality Measurement and Inherent Design Standard Deviation