on the fundamentals of track lateral resistance - arema · pdf filethe paper will present a...

On the Fundamentals of Track Lateral Resistance

ABSTRACT

A key aspect of track lateral stability assurance is the provision of adequate lateral resistance to

the rail-tie structure by the ballast. When lateral resistance is reduced, such as when ballast is

worked, the track cannot only lose alignment and surface, but can become buckling prone in the

presence of high thermal forces. Current methods to restore ballast strength after track work is

through mechanical compaction through dynamic track stabilization (DTS) or through traffic (train

load/tonnage) induced consolidation. Research has confirmed the effectiveness of DTS, however,

due to the complex nature of ballast compaction mechanics under train loads, a reliable

quantification of the effectiveness of train/tonnage based consolidation is still missing.

This paper presents a review of the fundamentals of track lateral resistance, its measurement and

its key influencing parameters, provides a test/data summary of US measurements to date,

present analysis results on influence on track stability, and offers insights on research needs for

further research studies for track lateral resistance improvements.

Key Words: track lateral resistance, ballast maintenance, track buckling, track shift, lateral

resistance measurement, STPT, track stabilization

Word Count: 4253

Andrew Kish, Ph.D. President - Kandrew Inc. Consulting Services

Peabody, MA, USA Phone: 978-535-3342

Email: [email protected]

© 2011 AREMA ®

1.0 INTRODUCTION

Track resistance is one of the most important parameters influencing track performance and

safety. Through its three in-plane components of lateral, longitudinal, and torsional, and one out-

of-plane of vertical, it influences most track lateral stability aspects including geometry retention

and buckling prevention. The three in-plane components are schematically shown in Figure 1

with their typical “spring” analogy representations.

Figure 1- Track Lateral Resistance Spring Analogy Longitudinal resistance provided to the rail/tie structure by fasteners and anchors is important to

prevent rail running (and thus limit rail neutral temperature variation), and to limit tensile break

gap sizes in the event of rail breaks. Torsional resistance provided by the spiked tie plates,

anchors and fasteners against rail rotation (in-plane-bending) also offers “rigidity” to the track

structure, especially against buckling.

Lateral resistance is the reaction offered by the ballast against lateral movement, often referred to

as the “lateral strength”. It is a tie-ballast interaction parameter which is influenced by several

factors such as ballast section, condition, consolidation, maintenance, tie type and condition, and

train loads. As such, track lateral resistance becomes a fundamental but highly variable

parameter in track lateral stability assurance, and is the focus of this paper.

P

P

P

P

Lateral spring

Torsional spring Longitudinal spring

Track Resistance Parameters

§ Lateral resistance (ties against ballast)

§ Longitudinal resistance (rails through fastenersand ties through ballast)

§ Torsional resistance (fasteners resisting rail rotation)

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

Lateral springLateral spring

Torsional springTorsional spring Longitudinal springLongitudinal spring





P

P

P

P

Lateral spring

Torsional spring Longitudinal spring





P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

Lateral springLateral spring

Torsional springTorsional spring Longitudinal springLongitudinal spring





© 2011 AREMA ®

The paper will present a review of the fundamentals of track lateral resistance, its measurement

and parametric influences, provide a test/data summary of US measurements to date, present

analysis results on influences on track stability, and offer insights on research needs for further

quantification studies for track stability safety and maintenance improvements.

2.0 LATERAL RESISTANCE FUNDAMENTALS

2.1 Basic Response Characteristics

As indicated in Figure 1, lateral resistance can be envisioned as a “spring” load-deflection

response characteristic representing tie-ballast interaction. As over 30 years research and tests

have confirmed, it is a load versus deflection non-linear “spring” response as illustrated in Figure

2, including a simplified analytic representation.

Figure 2 – Lateral Resistance Load Deflection Characteristics

Key features include an initial linear stiffness, a peak (break-away) value, and a decreasing

(drooping) portion to a constant “limit” value. Representations of typical “strong”, “average”,

“weak” behaviors for concrete ties are also shown. Key parameters/conditions influencing the

behavior include: tie type, weight, shape and spacing; ballast type/condition (fouled, wet, frozen,

0 1 2 3 4

Displacement (in)

0

500

1000

1500

2000

2500

3000

3500

Ap

pli

ed

Lo

ad

(lb

s)

Limit Resistance

weak

Initial Stiffness average

Peak Resistance

strong

0 1 2 3 4

Displacement (in)

0

500

1000

1500

2000

2500

3000

3500

Ap

pli

ed

Lo

ad

(lb

s)

Limit Resistance

weak



Peak Resistance

strong

0 1 2 3 4

Displacement (in)

0

500

1000

1500

2000

2500

3000

3500

Ap

pli

ed

Lo

ad

(lb

s)

Limit Resistance

Initial Stiffness

Peak Resistance

Idealization

0 1 2 3 4

Displacement (in)

0

500

1000

1500

2000

2500

3000

3500

Ap

pli

ed

Lo

ad

(lb

s)

Limit Resistance

Initial Stiffness

Peak Resistance

Idealization

© 2011 AREMA ®

etc.), shoulder width, crib content; maintenance, degree of consolidation, and train loads. Typical

values and ranges are shown in Figure 3.

Figure 3 – Typical Peak Lateral Resistance Values

Lateral resistance has three contributing components of bottom friction (Fb), side friction (Fs), and

end or shoulder restraint (Fe), and their approximate contributions are as indicated in Figure 4. As

research has shown, the bottom friction component is most influenced by tie type and weight, the

side friction by crib content, and the end restraint by ballast shoulder geometry. Consolidation and

compaction influence all of the three components to different degrees.

Figure 4 – Lateral Resistance Components

2.2 Lateral Resistance Measurement

Over the years several measurement techniques have been developed, including:

• single tie push test (STPT)

Fside Fbottom Fend

F F = Fs + Fb + Fe

20-25%35-40%30-35%Fside Fbottom Fend

F

Fside Fbottom Fend

F F = Fs + Fb + Fe

20-25%35-40%30-35%

F = Fs + Fb + FeF = Fs + Fb + FeF = Fs + Fb + Fe

20-25%35-40%30-35%

Typical concrete tie peak values (static)

1800 2000 2200 2400 2600 2800 3000 3200 3400 3600

Weak Marginal* Average Strong

7.5 10.0 12.5 15.0

lbs/tie

kN/tie

Note: for timber ties subtract 500 lbs/tie * Typical consolidation range


1800 2000 2200 2400 2600 2800 3000 3200 3400 3600

Weak Marginal* Average StrongStrong

7.5 10.0 12.5 15.0

lbs/tie

kN/tie


© 2011 AREMA ®

• discrete cut panel pull test

• continuous track panel pull test (TLPT)

• continuous dynamic measurement (Plasser-DGS)

• analytic empirical model

The most advantageous and frequently used technique is the STPT which mobilizes a single tie

in the ballast and measures the force versus displacement behavior as shown in Figure 1. This

provides the non-linear “spring” type characteristic required in track stability analyses. Figure 5

shows the STPT device developed by the Volpe Center in the US, and for detailed descriptions

refer to [1, 2].

The discrete cut panel pull test requires cutting rails and is highly destructive, while the TLPT

measures an entire continuous panel’s load-deflection response which includes the rail flexural

rigidity, the rail thermal force, and the non-uniform resistance offered by several ties. Thus from

TLPT data the single tie resistance is not calculable. The recently developed continuous

measurement technique through Plasser’s Dynamic Track Stabilizer (DTS, DGS) is an indirect

measurement relating the DTS energy output to the “frictional power” to move ballast in the track

grid. For a more detailed description on this measurement and tests refer to [3, 4]. The analytic

empirical model is lateral resistance estimator based on empirical equations developed through

over 500 STPT measurements in the US which evaluated the influences of shoulder width, crib

content, and consolidation levels on lateral resistance for both wood and concrete ties in granite

ballast. The model is available in the CWR-INDY module of the CWR-SAFE program which is

discussed in 4.2.

© 2011 AREMA ®

Figure 5 – Single Tie Push Test (STPT) Measurement

2.3 Concept of “Dynamic” Lateral Resistance and Tie/Ballast Friction Coefficient Train loads and dynamics play a key role in track lateral stability behavior due to their impact on

lateral resistance. Dynamic lateral resistance refers to the increase/decrease in resistance due to

train loads as illustrated in Figure 6.

Figure 6 – Dynamic Resistance Concept

The impact of dynamic uplift is that a percentage of the tie bottom component can be lost,

whereas under load the resistance is increased. This increase has been shown to be related to a

tie-ballast friction coefficient parameter, µ, as indicated in Figure 7, and as discussed in [5, 6].

Based on resistance measurements on vertically loaded ties, this parameter has been shown to

Dynamic Uplift

Reduced ResistanceIncreased Resistance Increased Resistance

Dynamic Uplift


Dynamic Uplift


© 2011 AREMA ®

be vertical load and tie type/condition dependent. The parameter µ plays an important role in both

buckling and track shift analyses as discussed later.

Figure 7 – Dynamic Resistance Friction Coefficient Behavior

Another aspect of dynamic lateral resistance is the influence of train induced vibration. Although

the effect is difficult to measure and quantify, tests by British Rail under the ERRI/D202 work

indicated a 25-50% reduction in lateral resistance depending on the acceleration and vibration

frequency levels [7]. Such reductions are currently not included in track stability analyses, and

further quantification would be most useful for US heavy tonnage tracks/equipment.

3.0 LATERAL RESISTANCE AND BALLAST CONSOLIDATION

When lateral resistance is reduced, such as when ballast is worked, the track can not only lose

alignment and surface, but can become buckling prone in the presence of high thermal forces.

Current methods to restore ballast strength after track work are through dynamic track

stabilization (DTS), or through traffic (train-load) induced consolidation. Research has shown both

methods to be effective to various degrees, however due to the complex nature of ballast

Fdyn = Fstat + µRV

RV

Fdyn

RV

Friction coefficient, µ, is a tie bottom roughness index

Fdyn = Fstat + µRV

RV

Fdyn

RV


Fdyn = Fstat + µRV

RV

Fdyn

RV


© 2011 AREMA ®

compaction mechanics under train loads and to its many influencing components, a reliable

quantification of MGT effectiveness is still missing. Such information is a prerequisite for the

effective placement and removal of slow orders. Key points addressing ballast lateral resistance

restoration include:

• Surfacing and tamping can reduce track lateral resistance (TLR) by 40-70%. The actual

amount depends on ballast type, ballast section/condition, wood vs. concrete ties, tie

design and condition, etc, i.e. on the initial conditions before surfacing. It also depends on

the nature of the ballast disturbance/work. As an example in the case of surfacing, the

amount of lift is considered to have a large influence. Therefore the key issues are: (1)

how much is the reduced resistance from which resistance restoration is required, (2)

how fast can it be regenerated to “safe” levels, and (3) what are the safe levels?

• DTS has been shown to regenerate 30-50% of resistance (from the reduced value)

based on European data. Limited US data is in the similar range, as discussed in 3.2.

• DTS tonnage equivalent (European tests – UIC Leaflet #720) is on the order of 0.1 MGT

(million gross tons) of traffic. However this equivalence has not been conclusively

demonstrated for US tracks/conditions as indicated in 3.2.

3.1 Ballast Consolidation Mechanism

For DTS the basic mechanism for resistance restoration is a “reintensification of the tie-bottom

contact”. The DTS horizontal vibratory input under a specified vertical load causes a dynamic re-

arrangement of the ballast particles and an increases tie-bottom contact area [3]. Such tie–bottom

contact restoration effectively increases the tie/ballast friction coefficient represented in Figure 7,

as well as assures the 35-40% tie bottom resistance contribution as referred to in Figure 4.

© 2011 AREMA ®

Train traffic induced (MGT) consolidation is however a different mechanism altogether. The wheel

induced dynamic uplift versus downward pressure coupled with vertical vibration input presents a

different compaction mechanics mode, and remains a minimally researched topic to date. Hence

the questions to resolve include: (1) how traffic tonnage consolidates (by what mechanism), and

(2) how effectively (at what tonnage rate)?

3.2 US Data on Maintenance, DTS and MGT Influences on Lateral Resistance

Over the past 30 years the US railroads, the US DOT’s Volpe Center, and the Association of

American Railroads have conducted numerous STPT tests to evaluate lateral resistance

behavior. Aside from the fundamental mechanistic aspects, a large focus was placed on

evaluating the influences of maintenance and subsequent restoration of lateral resistance through

DTS and tonnage. The following is a brief synopsis of some applicable results:

1. Chessie and Amtrak Tests – concrete ties (1985, Sluz, [8])

a. Chessie: 9% recovery after 0.076MGT

b. Amtrak: 11% recovery after 0.073MGT

2. AAR/TTC Tests – wood ties (1990 – Trevizo, [9])

a. Tangent: 17% recovery after 0.1MGT; 32% after 1MGT

b. 5° Curve: 9% recovery after 0.1MGT; 21% after 1MGT

3. Volpe/FRA Tests at TTC - wood and concrete (1987-1990; Kish, et al, [10])

a. Wood - tangent: 26% recovery after 0.1MGT

b. Concrete – 5° Curve: 52 % reduction due to tamping

c. Concrete – 5° Curve: 22% recovery after 0.1MGT

© 2011 AREMA ®

4. Volpe/Union Pacific Tests – concrete (2000-Sluz, [11])

a. Concrete (new-scalloped) -17% recovery after 0.35MGT

b. DTS increase - 33%

5. Volpe/Amtrak/FRA Tests – concrete (2001- Kish, et al, [12, 13])

a. 43% reduction due to surfacing with ½ inch lift

b. DTS increase: 31%

6. UP/Foster-Miller Tests – wood/concrete/old/new/DTS (2001-Samavedam [14])

a. 39-70% reduction due to tamping/surfacing

b. 0.1MGT had negligible influence on wood after tamping; 0.2MGT was 28%

c. DTS increase on concrete: 22%

d. After DTS, traffic decreased lateral resistance initially, then it increased

e. Heavy rain/wet ballast: 20% decrease in lateral resistance on wood

Some key features of items 3 and 5 are illustrated in Figures 8 and 9. As the above summary

indicates there is a large variability on traffic/MGT influence on track lateral resistance recovery

after maintenance, and it appears that a larger than 0.1 MGTs may be required for a DTS

equivalent of 30-50% lateral resistance restoration. Thus while the DTS benefits are relatively

reliable and consistent, there are several traffic/tonnage based consolidation issues/questions not

resolved to date. These include: (1) is there a train speed influence on consolidation, (2) is there

an axle load influence, (3) is there a curvature influence, (4) is there a track material influence i.e.

ballast type, tie type, etc., and (5) is there an “initial condition” influence i.e. for example a skin lift

might produce a 30% decrease in resistance, whereas a major surfacing might be a 60%

reduction, both requiring different recovery rates. Tests are needed to better evaluate and

quantify these parameters/conditions. The key railroad impact issue is that there is an urgent

need for such data to manage speed restrictions after maintenance quickly an effectively without

compromising safety.

© 2011 AREMA ®

Figure 8 – Concrete Tie MGT Consolidation Tests at FAST (Ref. 10)

Figure 9 – Concrete Tie Track Stabilization Tests on Amtrak/New Carrollton (Ref. 12)

0

5

10

15

20Min: 1700Max: 2200Mean: 1926Std Dev: 136Count: 42

Post-Maintenance(surfacing)

0

5

10

15

20

Min: 2200Max: 2900Mean: 2520Std Dev: 240Count: 35

Post-DTS

0

5

10

15

20


No DTS- 3,360 Tons Traffic

Nu

mb

er

of

ST

PT

s

Pre-Maintenance

0

5

10


1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000

Peak lateral resistance (lbs/tie)

0

5

10

15

20

0

5

10

15


Post-Maintenance(surfacing)

0

5

10

15

20

0

5

10

15

20


Post-DTS

0

5

10

15

20


No DTS- 3,360 Tons Traffic

Nu

mb

er

of

ST

PT

s

Pre-Maintenance

0

5

10


1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000

Peak lateral resistance (lbs/tie)

Consolidation (MGT)

0 2 4 6 8 10

Pe

ak la

tera

l resis

tance

incre

ase

(lb

s/tie

)

0

200

400

600

800

1000

1200

1400

Fitted equation

Data

Initial tamped@ 2300lbs/tie

Note: At each MGT increment an average of 15 STPTs is shown

22% increase due to 0.1MGT

52% loss due to tamping @ 9.7MGTs

Peak

late

ral r

esi

stance incr

ease a

fter

tam

pin

g (

lbs/

tie)

Consolidation (MGT)

0 2 4 6 8 10

Pe

ak la

tera

l resis

tance

incre

ase

(lb

s/tie

)

0

200

400

600

800

1000

1200

1400

Fitted equation

Data





Consolidation (MGT)

0 2 4 6 8 10

Pe

ak la

tera

l resis

tance

incre

ase

(lb

s/tie

)

0

200

400

600

800

1000

1200

1400

Fitted equation

Data





Peak

late

ral r

esi

stance incr

ease a

fter

tam

pin

g (

lbs/

tie)

© 2011 AREMA ®

4.0 LATERAL RESISTANCE INFLUENCE ON TRACK STABILITY

Track lateral stability assurance requires effective lateral strength management. The track

stability mechanism features are outlined in Table 1, where track lateral resistance is a contributor

to all three events of the lateral stability mechanism.

Table 1 – Track Lateral Stability Mechanism

The mechanistic difference between track shift and track buckling is in the principal load

mechanism producing the event, namely the many cycles of L/V’s for track shift versus the high

longitudinal forces for track buckling. Also, track buckling typically requires the presence in initial

line defects which are usually generated by track shift. Both track shift and track buckling events

are highly impacted by lateral resistance, but in different aspects as discussed below.

1) High L/V’s2) Reduced local lateral resistance3) Initial imperfections (welds), construction

anomalies, and install errors

1 Formation of initialtrack misalignments

1) Increase in L/V, and high longitudinal forces2) Reduced lateral resistance at line defects3) Track “dynamic uplift”4) Many cycles of L/V’s

2Growth of

misalignments(Track Shift)

1) High longitudinal force2) Reduced TN (stress-free temperature)3) Weakened lateral resistance4) Train loads and dynamics5) Misalignments generated by track shift

3 Buckling

Event Major causal factorsStage

Track Lateral Stability Mechanism





2Growth of



3 Buckling



© 2011 AREMA ®

4.1 Lateral Resistance Influence on Track Shift and Lateral Alignment Retention

Track lateral shift is the formation and growth of lateral track misalignments due to high lateral to

vertical load ratios (net axle L/V’s or NAL’s) coupled with longitudinal forces. Usually many axle

passes and high L/V’s are required to produce a misalignment. Typical description of track shift is

in terms of cumulative lateral deflections versus the number of axle passes is shown in Figure 10

together with the influencing parameters, including the lateral resistance components.

Figure 10 - Track Lateral Shift Parameters and L/V Response

The lateral resistance function and its idealization for track shift analyses have to account for both

the loaded and unloaded resistance, hence the importance of the tie/ballast friction coefficient

parameter. Figure 11 depicts the lateral resistance elements for track shift. As research has

shown, the key lateral resistance parameters for the determination of cumulative deflection due to

net axle L/Vs are the slopes defining the elastic and the peak limits as indicated by Fe, we, Fp and

wp on Figure 11. The lateral resistance elastic limit (Fe and we) is most important in track shift

response because it governs the ballast load-unload hysteresis characteristics, hence the

residual deflections. The analysis to predict track lateral shift response is by the US DOT/Volpe

model called TREDA (short for Track Residual Deflection Analysis). For a detailed description of

0.0

0.1

0.2

0.3

0.4

0.5C

um

ula

tiv

e lat

era

lre

sid

ua

l de

fle

ctio

n (

in)

0 100 200 300 400 500

Number of axle passes

Low L/V

Moderate L/V

High L/V

• Rail section properties

• Thermal load

• Track type and curvature

• Initial misalignments

• Vertical foundation modulus

• Type of load and number of load cycles (axle passes)

• Tie lateral resistance: (with and without vertical load)

Ø Elastic limit: load/unloadhysteresis loop

Ø Tie ballast friction coefficient

Track Lateral Shift Response and Parameters

0.0

0.1

0.2

0.3

0.4

0.5C

um

ula

tiv

e lat

era

lre

sid

ua

l de

fle

ctio

n (

in)

0 100 200 300 400 500


Low L/V

Moderate L/V

High L/V

0.0

0.1

0.2

0.3

0.4

0.5C

um

ula

tiv

e lat

era

lre

sid

ua

l de

fle

ctio

n (

in)

0 100 200 300 400 500


Low L/V

Moderate L/VModerate L/V

High L/V


• Thermal load









• Thermal load








Track Lateral Shift Response and Parameters

© 2011 AREMA ®

TREDA, its validation, parametric studies, and for its applications to determine maximum

allowable L/Vs to prevent excessive residual lateral displacements refer to [5, 6, 15, 16].

Figure 11 – Lateral Resistance Elements for Track Shift Analysis

An example on the influence of lateral resistance elastic limit on track lateral deflection response

is illustrated in Figure 12. The response is highly elastic limit dependent, and the figure shows

that for the parameters chosen to represent a “weak” resistance, 2° curve, concrete tie track

under summer conditions, an L/V=0.5 (vertical axle load of 55kips and a lateral axle load of 27.5

kips) is not permissible due incurring progressive lateral deflections.

Lateral Deflection, W

Late

ral R

esis

tan

ce, F

WpWe

Fe

Fp

Slope, K2

Slope, K1

Fp (stat)

Unloaded tie

Fe

We Wp


Fp (dyn)

µ • Rv

Loaded tie

Tie ballastfrictioncoefficient

Tie load


Late

ral R

esis

tan

ce, F

WpWe

Fe

Fp

Slope, K2

Slope, K1

Fp (stat)

Unloaded tie

Fe

We Wp


We Wp


Fp (dyn)

µ • Rv

Loaded tie


Tie load

© 2011 AREMA ®

Figure 12 – Elastic Limit Influence on Track Shift Response

4.2 Lateral Resistance Influence on Track Buckling

It is well established that track lateral resistance plays a key role in track buckling. Many buckling

derailments are attributable all or in part to weakened ballast condition, hence to a reduced lateral

resistance. In order to better portray the impact of lateral resistance on track bucking, it is

important to provide a brief synopsis of track buckling fundamentals.

4.2.1 The Buckling Mechanism

Track bucking is best described through a stability diagram that portrays all the positions of

equilibrium as illustrated in Figure 13 in terms of temperature increase above neutral (TN) versus

lateral displacement.

0 10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Resid

ual d

eflection (

in)


We1=0.005 in.

We1=0.03 in.

We1=0.05 in.

We1=0.015 in.

2° curve

concrete tie track

136RE rail

24 in. tie spacing

Kv=10000 psi

Fp=2000 lbs, wp=0.30 in.

Fe=1500 lbs, we1=varies

we2=0.1 in.

µ1=0.9, µ2=0.75, L/V=0.5

∆T=50°F, V=55 kips

constant lateral force

5000

0 10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Resid

ual d

eflection (

in)


We1=0.005 in.We1=0.005 in.

We1=0.03 in.We1=0.03 in.

We1=0.05 in.We1=0.05 in.

We1=0.015 in.

2° curve

concrete tie track

136RE rail

24 in. tie spacing

Kv=10000 psi

Fp=2000 lbs, wp=0.30 in.


we2=0.1 in.

µ1=0.9, µ2=0.75, L/V=0.5

∆T=50°F, V=55 kips


5000

2° curve

concrete tie track

136RE rail

24 in. tie spacing

Kv=10000 psi

Fp=2000 lbs, wp=0.30 in.


we2=0.1 in.

µ1=0.9, µ2=0.75, L/V=0.5

∆T=50°F, V=55 kips


5000

© 2011 AREMA ®

Figure 13 – Track Buckling Mechanism Stability Behavior

The two equilibrium positions of interest are the peak and minimum points on the curve denoted

by Tbmax and Tbmin which define the “buckling regime” in which buckling takes place. Tbmin is

referred to as the “safe allowable temperature increase” in accordance with structural stability

criterion. Current track buckling safety criterion is in fact based on Tbmin plus a safety factor [17].

As expected, Tbmax,Tbmin and the buckling regime are highly track parameter dependent, where

one key parameter is lateral resistance.

4.2. 2 Lateral Resistance Influence on Buckling Temperatures

Over the years numerous analytic studies have been performed on evaluating lateral resistance

parametric aspects on buckling temperatures [2, 18], and here just a few salient points will be

illustrated. It is most important to recognize the importance and influence of both the peak and the

limit resistances which is illustrated in Figure 14 and described in [18]. Principally, the peak

resistance controls Tbmax, where as the limit resistance strongly influences Tbmin, the safe

temperature increase value. Hence since Tbmin determines buckling safety through Tall, the

knowledge of the full lateral characteristic is critical.

Lateral Displacement

TR

TN

Safe Allowable

Temperature Increase

(BUCKLING STRENGTH)

Buckling

regime

Tbmin

Tbmax

BUCKLE

Low Speed

High Speed


TR

TN


TR

TN


TR

TN

BUCKLE

Low Speed

High Speed

Safe AllowableTemperature Increase, Tall

(BUCKLING STRENGTH)

Buckling regime

Tbmax

Tbmin

TR

TN


TR

TN


TR

TN


TR

TN

TR

TN

Safe Allowable

Temperature Increase

(BUCKLING STRENGTH)

Buckling

regime

Tbmin

Tbmax

BUCKLE

Low Speed

High Speed


TR

TN


TR

TN

TR

TN


TR

TN

TR

TN


TR

TN

BUCKLE

Low Speed

High Speed

Safe AllowableTemperature Increase, Tall

(BUCKLING STRENGTH)

Buckling regime

TbmaxTbmax

Tbmin

TR

TN

© 2011 AREMA ®

Figure 14 – Peak and Limit Resistance Impacts on Buckling Temperatures Since in most practical applications it’s difficult to evaluate the large displacement limit resistance

values, correlation statistics have been developed to afford easier analytic treatments. The

resulting empirical relationships are based on the over 500 STPT measurement in the US, both at

TTC/FAST and in revenue service. Additional correlations with similar results were established by

British Rail (BR) and Deutsche Bahn (DB) [19]. The US measured correlation equations relating

FP and FL are given from [2] as:

Buckling analyses embodying the non-linear aspects of the lateral resistance and its tie/ballast

friction coefficient based dynamic effects are available through the US DOT/Volpe Center

developed CWR-SAFE model [20]. Some key lateral resistance parametric influences are

illustrated below.

0 1 2 3 4

Displacement, w (in)

0

500

1000

1500

2000

2500

3000

3500

Late

ral R

esis

tan

ce

, F

(lb

s)

Peak Resistance, FP

Limit Resistance, FL

WP WL


TR

TN

Bucklingregime

Tall

Tbmax

Tbmin

0 1 2 3 4

Displacement, w (in)

0

500

1000

1500

2000

2500

3000

3500

Late

ral R

esis

tan

ce

, F

(lb

s)

Peak Resistance, FP


WP WL


TR

TN

Bucklingregime

Tall

Tbmax

Tbmin

Concrete

<

≥+=

1530 lbs FifF

lbs1530Fiflbs950F38.0F

PP

PP

L

<

≥+=

715 lbsFifF

715 lbsFiflbs500F3.0F

PP

PP

L

Wood Concrete

<

≥+=

1530 lbs FifF

lbs1530Fiflbs950F38.0F

PP

PP

L

<

≥+=

715 lbsFifF


PP

PP

L

<

≥+=

715 lbsFifF


PP

PP

L

Wood

© 2011 AREMA ®

(a) Buckling Response Behavior for “Weak”, “Average” and “Strong” Resistance Tracks

Figure 15 shows the buckling response comparison for a 136# CWR wood tie 5 deg curve track

with FRA Class 4 line defects when the lateral resistances for “weak”, “average” and “strong”

conditions are as shown in the right hand side of the figure. The difference in the respective

buckling regimes is evident. In fact, for the weak resistance condition there is no buckling regime

indicating a highly unstable condition as evidenced by the progressive lateral displacements with

temperature. Thus the inference from the figure is that for this track type/condition the “strong”

resistance track buckles in between 100 – 140°F above neutral, “average” resistance between 87

and 94°F, and “weak” resistance track does not buckle in the conventional sense, but

progressively shifts with temperature, indicating a highly unstable and unsafe condition.

Figure 15 – Lateral Resistance Influence on Bucklin Temperatures for Weak, Average and Strong Track Conditions

wood tie track136RE rail5 deg curve20 in. tie spacingGranite, µ=1.20Kv=6000 psiKf=200 psiτo=120 in-kips/rad/in

δo=1.5 in. Lo=180 in

Input parameters

0.25

2000

3600 Strong LateralResistance

1600

0.35

2400

0.5

1400

Average LateralResistance

Weak LateralResistanceT

em

pe

ratu

re in

crea

se a

bo

ve n

eu

tra

l (°F

)

0 2 4 6 8 10 12 14 160

20

40

60

80

100

120

140

Lateral displacement (in)

Large BucklingRegime

Small BucklingRegime

Strong LateralResistance


Weak LateralResistance

(No Buckling Regime)



Input parameters



Input parameters

0.25

2000

3600

0.25

2000

0.25

2000

3600 Strong LateralResistance

1600

0.35

2400

1600

0.35

2400

0.5

1400


Weak LateralResistanceT

em

pe

ratu

re in

crea

se a

bo

ve n

eu

tra

l (°F

)

0 2 4 6 8 10 12 14 160

20

40

60

80

100

120

140

Lateral displacement (in)

Large BucklingRegime

Small BucklingRegime

Strong LateralResistance


Weak LateralResistance

(No Buckling Regime)

© 2011 AREMA ®

(b) Influence of Lateral Resistance on “Safe” Temperatures for Buckling Prevention

As discussed, lateral resistance is a highly variable parameter, and for concrete ties it typically

falls into the four peak resistance ranges: (1) less than 1900 lbs/tie for weak, recently maintained

conditions; (2) 1900 to 2500 for marginal conditions where consolidation is active; (3) 2500 to

3200 for average conditions, and (4) above 3200 for well maintained, fully consolidated tracks.

Figure 16 shows the influence of these 4 categories on “safe rail temperatures” for buckling

prevention for tangent and curved tracks with FRA Class 4 line defects and with a neutral

temperature of 60°F. Also shown on the figure is the measured data form the Volpe/AMTRAK

tests from Figure 9.

Figure 16 – Influence of Lateral Resistance on Safe Temperature Increase

Figure 16 indicates the importance and benefit of consolidation in terms of safe rail temperatures

by increasing it from a low 118°F to a more acceptable 134° for the 5 deg curve, and from 138°F

to 144°F for the tangent. Note that for higher neutral temperatures, the safe temperature values

increase correspondingly by the amount of the neutral temperature change.

Parameters: Tangent and 5° (350m radius) concrete tie track with Class 4 (38mm/10m) linedefect; 136# CWR; TN=60°F (16°C); variable lateral resistances

Safe rail temperature, Tall

90 100 110 120 130 140 150 160

1400

1800

2200

2600

3000

3400

3800

La

tera

l re

sis

tan

ce (

lbs

/tie

)

TN = 60°F(16°C)5 deg curve

5

10

15

La

tera

l res

ista

nc

e (k

N/tie

)

°F

°C40 50 60 7030

TypicalConsolidation Regime

Strong

Average

Weak

TN = 60°F(16°C)Tangent

Volpe/AMTRAKNew Carrollton Data

Before Surfacing

After DTS

After Surfacing



90 100 110 120 130 140 150 160

1400

1800

2200

2600

3000

3400

3800

La

tera

l re

sis

tan

ce (

lbs

/tie

)


5

10

15

La

tera

l res

ista

nc

e (k

N/tie

)

°F

°C40 50 60 7030


Strong

Average

Weak




90 100 110 120 130 140 150 160

1400

1800

2200

2600

3000

3400

3800

La

tera

l re

sis

tan

ce (

lbs

/tie

)


5

10

15

La

tera

l res

ista

nc

e (k

N/tie

)

°F

°C40 50 60 7030



Strong

Average

Weak



Before Surfacing

After DTS

After Surfacing

Before Surfacing

After DTS

After Surfacing

© 2011 AREMA ®

5.0 Conclusions and Recommendations 1. Track lateral resistance is a key parameter for lateral stability assurance. It is typically

represented through “spring” type load-deflection characteristics which are non-linear and highly

variable. The key descriptors are the “peak” and “limit” values which depend on: tie type, weight,

shape and spacing; ballast type/condition, shoulder width, crib content; ballast maintenance,

degree of consolidation, and train loads. It is measured most conveniently by a single-tie-push-

test (STPT) method which mobilizes the tie in the ballast and records the load-deflection

response.

2. Lateral resistance has both static and dynamic components. The dynamic characteristics

depend on the loaded and unloaded (dynamic uplift) frictional interface between tie and ballast as

represented by a tie/ballast friction coefficient parameter which is experimentally determined. It is

this dynamic resistance value that’s required in lateral stability analyses.

3. Ballast maintenance has a large influence on reducing lateral resistance which can be on the

order of 30-70%. Such reductions can cause damaging track failures through track buckling or by

excessive misalignments generated by track shift. In order to mitigate such failures, lateral

strength restoration is required through either mechanical (DTS) or train traffic (MGT) induced

consolidation.

4. Whereas DTS has proven to be an effective and efficient means to quickly restore 30-50% of

the reduced resistance, the train traffic (MGT) based consolidation may require tonnage levels

well in excess of the currently accepted 0.1 MGT equivalent, as US data indicates. Since even

the 0.1 MGT’s slow order traffic may be prohibitive for most railroads, more tests and analyses

are required to better evaluate the tonnage consolidation aspects. Such studies need to address

several ballast compaction mechanics issues, including the effects of axle loads and speeds on

© 2011 AREMA ®

consolidation, track curvature influences, track type/material/component influences, and recovery

rates required for lateral stability assurance.

5. Track lateral stability assurance requires addressing the two key failure modes of track

buckling and track shift. The track buckling safety limits in terms “allowable temperature increase

values” above neutral are strongly lateral resistance dependent, as are the actual buckling

temperatures. Hence restoration of reduced resistance due to maintenance to “safe” levels is a

key part of track buckling prevention. Such lateral strength restorations through dynamic track

stabilization (DTS) have proven to be quite effective, whereas the similar effects through tonnage

(MGT) require more evaluation and testing.

6. Mitigation of track shift and resulting unsafe alignment defects also require high lateral

resistances. The particular requirement is a high lateral resistance elastic limit, which can be

achieved through a high peak resistance value. The impact of such high elastic and peak values

is an allowance for higher net axle L/V’s and higher speeds.

REFERENCES

1. Samavedam, G. and A. Kish, “Continuous Welded Rail Track Buckling Safety Assurance

through Field Measurement of Track Resistance and Rail Force”, Transportation Research

Record 1289, pp.39-52

2. Kish, A. and G. Samavedam, “Track Buckling Prevention: Theory, Safety Concepts and

Applications”, US DOT/FRA Report, 2004, in FRA publication

3. Lichtberger, B, “Track Compendium”, Eurailpress, 2005, English Edition

© 2011 AREMA ®

4. Bosch van den, R, “Quervershiebewiderstandsmessung mit dem dynamischen

Gleisstabilitator“ in German, Eisenbahningenieur (58) 6/2007, pp. 15-19

5. Kish, A., G. Samavedam, and D. Wormley, “New Track Shift Safety Limits for High-Speed

Rail Applications”, Proceedings of World Congress on Railway Research, Cologne, Germany,

November 2001

6. Kish, A.,” New Track Shift Limits for High-Speed Rail” in French, German and English,

Schienen der Welt – Rail International, August-September, 2001, pp 36-41

7. Hunt, D and Z. Yu, “Measurement of Lateral Resistance Characteristics for Ballasted

Tracks”, ERRI D 202/DT 361 Report, February 1998, Utrecht, Netherlands

8. Sluz, A., TSC/Volpe Project Memorandum, 1985

9. Trevizo, C., “Restoration of Post Tamp Stability”, WP-150, AAR/TTCI Project Report, 1990

10. Kish, A., D. Clark, and W. Thompson, “Recent Investigations on the Lateral Stability of

Wood and Concrete Tie Tracks”, AREA Bulletin 752, Volume 96, October 1995

11. Sluz, A., “Evaluation of Dynamic Track Stabilization”, Volpe Project Technical

Memorandum, 2000

12. Kish, A., T. Sussmann, M. Trosino, “Effects of Maintenance Operations on Track Buckling

Potential”, Proceedings of International Heavy Haul Association, May 2003

© 2011 AREMA ®

13. Sussmann, T., A. Kish, M. Trosino, “Investigation of the Influence of Track Maintenance on

the Lateral Resistance of Concrete Tie Track”, Transportation Research Board Conference,

January 2003

14. Samavedam, D., “Track Resistance Measurements on the Union Pacific”, Union Pacific

Test Report, 2001

15. Kish, A and W. Mui, “TREDA – Track Residual Deflection Analysis”, Software and User’s

Guide, March 2001

16. Samavedam, G. and A. Kish, “Track Lateral Shift Model Development and Test Validation”,

DOT/FRA/ORD Report, February 2002

17. Kish, A and G. Samavedam, “Dynamic Buckling of Continuous Welded Rail Track:

Theory, Tests, and Safety Concepts,” Transportation Research Record No. 1289, “Rail: Lateral

Track Stability 1991”

18. Samavedam, G., A. Kish, A. Purple, and J. Schoengart, “Parametric Analysis and Safety

Concepts of CWR Track Buckling”, DOT/FRA/ORD-93/26, December 1993.

19. ERRI D202/DT 360, “Lateral Resistance Tests“, October 1997, Utrecht, Netherlands

20. Kish, A., G. Smavedam and K. Kasturi, “CWR-SAFE Version 2000,” Software and

User’s Guide, CD-ROM (Interim Version), Volpe Center, February 2001

© 2011 AREMA ®

LIST OF FIGURES

Figure 1- Track Lateral Resistance Spring Analogy

Figure 2- Lateral Resistance Load Deflection Characteristics

Figure 3- Typical Peak Lateral Resistance Values

Figure 4- Lateral Resistance Components

Figure 5- Figure 5 – Single Tie Push Test (STPT) Measurement

Figure 6- Dynamic Resistance Concept

Figure 7- Dynamic Resistance Friction Coefficient Behavior

Figure 8- Concrete Tie MGT Consolidation Tests at FAST (Ref. 10)

Figure 9- Concrete Tie Track Stabilization Tests on Amtrak/New Carrollton (Ref. 12)

Figure 10- Track Lateral Shift Parameters and L/V Response

Figure 11- Lateral Resistance Elements for Track Shift Analysis

Figure 12- Elastic Limit Influence on Track Shift Response

Figure 13- Track Buckling Mechanism Stability Behavior

Figure 14- Peak and Limit Resistance Impacts on Buckling Temperatures

Figure 15- Lateral Resistance Influence on Bucklin Temperatures for Weak, Average

and Strong Track Conditions

Figure 16- Influence of Lateral Resistance on Safe Temperature Increase

© 2011 AREMA ®

2011 ANNUAL CONFERENCESeptember 18-21, 2011 | Minneapolis, MN

Andrew Kish, Ph.D.Kandrew Inc. Consulting Services

Peabody, MA, USA


q Paper deals with track lateral resistance issues addressing track lateral stability management including maintenance, geometry retention and track buckling prevention.

Ø What is track resistance and key influencing parameters?Ø What impacts on track maintenance, track buckling, and track

shift?

Paper Content

• Track lateral resistance fundamentals• Lateral resistance and ballast stabilization• Lateral resistance influence on track stability• Key research needs for more effective management

Key Issues Addressed

Overview

Paper Overview, Content, and Key IssuesConsulting Services


Talking Points

• What is track lateral resistance, key components/parameters and how to measure?

• What maintenance aspects/requirements for consolidation?

• What US data on resistance restoration after ballast work?

• What impacts on track buckling and track shift?

• What research needs?

Presentation OutlineConsulting Services






2Growth of



3 Buckling



What is track lateral stability?

0.0

0.1

0.2

0.3

0.4

0.5

Cu

mu

lati

ve

late

ral

resid

ual d

efl

ecti

on

(in

)

0 100 200 300 400 500Number of axle passes

Low L/VModerate L/V

High L/V

High Axle Load Problem

TREDA

High Thermal Load Problem

CWR-SAFE

Consulting Services


TLR is the reaction offered by the ballast to therail-tie structure against lateral movement

g Definition:

Consulting Services

What is track lateral resistance (TLR)?

Ballast reaction (lb/tie)or (lb/in)

PP

P

P

P

P

Lateral spring

L


Consulting Services

How to Measure?




• continuous dynamic measurement (Plasser-DTS)

• analytic empirical model (CWR-SAFE)

Measurement Methods




• continuous dynamic measurement (Plasser-DTS)

• analytic empirical model (CWR-SAFE)*

√

* Model “trained” by over 1000 STPT measurements to provide lateralresistance based on inputs of: tie type, shoulder width, crib content, and consolidation


0 1 2 3 4

Displacement (in)

0

500

1000

1500

2000

2500

3000

3500

4000

Ap

plied

Lo

ad

(lb

s)

Limit Resistance

weak


Peak Resistance

strong

Consulting Services

Typical Behavior and Values

0 1 2 3 4

Displacement (in)

0

500

1000

1500

2000

2500

3000

3500

Ap

plied

Lo

ad

(lb

s)

Limit Resistance

Initial Stiffness

Peak Resistance

Idealization


1800 2000 2200 2400 2600 2800 3000 3200 3400 3600

Weak Marginal* Average Strong

7.5 10.0 12.5 15.0

lbs/tie

kN/tie



§ Tie type, weight, shape and spacing; ballast type andcondition (fouled, frozen, etc.) shoulder width, crib content; maintenance, degree of consolidation, and vehicle loads (dynamic uplift)

Consulting Services

Factors Influencing Lateral Resistance



Dynamic Uplift


25%

35%

40%

Can result up to 40% loss of lateral resistance

% Contribution Rule of Thumb


Consulting Services

Track Dynamic Resistance: Tie/Ballast Friction Coefficient

Fdyn = Fstat + µRV

RV

Fdyn

RV


• Friction coefficient µ is a key parameter in both track buckling and track shift analyses


• Ballast maintenance can reduce TLR by 40 - 70%; requires consolidation either by dynamic track stabilization (DTS) or traffic. DTS can increase value by 30 – 40%; traffic consolidation may require over 0.1 MGTs (million gross tons) of traffic coupled with slow-orders.

Vertical load (1400 psi hydraulic pressure)

Horizontal vibration (30 Hz)

Speed: 1mph

DTS principle: a quick restoration of the tie bottom friction component of lateral resistance by applying vertical load coupled with horizontal vibration

Consulting Services

Influence of Ballast Maintenance

• Initial assumption on traffic consolidation: 0.1 MGT = 30-40% DTS

Has not been demonstrated by US experience!


Consulting Services

US Data on Ballast Consolidation

Chessie and Amtrak Tests – concrete ties (1985, Sluz, [8])• Chessie: 9% recovery after 0.076MGT• Amtrak: 11% recovery after 0.073MGT

AAR/TTC Tests – wood ties (1990 – Trevizo, [9])• Tangent: 17% recovery after 0.1MGT; 32% after 1MGT• 5° Curve: 9% recovery after 0.1MGT; 21% after 1MGT

Volpe/FRA Tests at TTC - wood and concrete (1987-1990; Kish, et al, [10])• Wood - tangent: 26% recovery after 0.1MGT• Concrete – 5° Curve: 52 % reduction due to tamping• Concrete – 5° Curve: 22% recovery after 0.1MGT

Volpe/Union Pacific Tests – concrete (2000-Sluz, [11])• Concrete (new-scalloped) - 17% recovery after 0.35MGT • DTS increase - 33%

Volpe/Amtrak/FRA Tests – concrete (2001- Kish, et al, [12, 13])• 43% reduction due to surfacing with ½ inch lift• DTS increase: 31%

UP/Foster-Miller Tests – wood/concrete/old/new/DTS (2001-Samavedam [14])• 39-70% reduction due to tamping/surfacing• 0.1MGT had negligible influence on wood after tamping; 0.2MGT was 28%• DTS increase on concrete: 22%• After DTS, traffic decreased lateral resistance initially, then it increased• Heavy rain/wet ballast: 20% decrease in lateral resistance on wood

Chessie and Amtrak Tests – concrete ties (1985, Sluz, [8])• Chessie: 9% recovery after 0.076MGT• Amtrak: 11% recovery after 0.073MGT

AAR/TTC Tests – wood ties (1990 – Trevizo, [9])• Tangent: 17% recovery after 0.1MGT; 32% after 1MGT• 5° Curve: 9% recovery after 0.1MGT; 21% after 1MGT

Volpe/FRA Tests at TTC - wood and concrete (1987-1990; Kish, et al, [10])• Wood - tangent: 26% recovery after 0.1MGT• Concrete – 5° Curve: 52 % reduction due to tamping• Concrete – 5° Curve: 22% recovery after 0.1MGT

Volpe/Union Pacific Tests – concrete (2000-Sluz, [11])• Concrete (new-scalloped) - 17% recovery after 0.35MGT• DTS increase - 33%

Volpe/Amtrak/FRA Tests – concrete (2001- Kish, et al, [12, 13])• 43% reduction due to surfacing with ½ inch lift• DTS increase: 31%

UP/Foster-Miller Tests – wood/concrete/old/new/DTS (2001-Samavedam [14])• 39-70% reduction due to tamping/surfacing• 0.1MGT had negligible influence on wood after tamping; 0.2MGT was 28%• DTS increase on concrete: 22%• After DTS, traffic decreased lateral resistance initially, then it increased• Heavy rain/wet ballast: 20% decrease in lateral resistance on wood

0.1 MGT traffic does not

produce the DTS equivalent,

but LOWER!

More R&Dand tests are

required to better quantify tonnage

based consolidation


Consulting Services

What resistance is required?

(1) The % recovery is important, but MORE important are the actual values i.e. wherefrom and where to?

(a 35% recovery from 1800 lbs/tie is different than a 35% recovery from 2300 lbs/tie)

(2) What is the minimum resistance required for buckling safety?

Answer: depends on track parameters and conditions!

• Track curvature

• Track alignment

• Track neutral temperature

Need to know/measure absolute values!

Key Notes/Questions


Parameters: 5° (350m radius) curve; concrete tie track with Class 4 (38mm/10m)line defect; US-136# CWR; variable lateral resistances CWR-SAFE

Consulting Services

Minimum Resistance for Buckling Safety

90 100 110 120 130 140 150 160

1400

1800

2200

2600

3000

3400

3800Strong

Average

Marginal

Safe allowable rail temperature

Late

ral re

sis

tan

ce (

lbs/t

ie)

Weak

TN = 60°F(16°C)

TN = 70°F

TN = 90°F

TN = 80°F

TN = 100°F (38°C)

TN = 50°F

5

10

15

Late

ral re

sis

tan

ce (k

N/tie

)

°F

°C40 50 60 7030


Parameters: Tangent and 5° (350m radius) concrete tie track with Class 4 (38mm/10m) line defect; 136# CWR; TN=60°F (16°C); variable lateral resistances


90 100 110 120 130 140 150 160

1400

1800

2200

2600

3000

3400

3800

La

tera

l re

sis

tan

ce (

lbs/t

ie)


5

10

15

La

tera

l resis

tan

ce (k

N/tie

)

°F

°C40 50 60 7030


Strong

Average

Weak


Consulting Services

Influence of Track Stabilization on Buckling Safety

Lateral deflection, δ

∆Τ

TBmin

T Bmax

Buckling Regime

BUCKLE

Lateral deflection, δ

∆ T

T Bmin

T Bmax

BucklingRegime re

BUCKLE

Track quality: MARGINAL

Track quality: AVERAGE

(Safe Temp Increase)

Realized Benefit Is MORE!!

Before Surfacing


After DTS

After Surfacing


§ Track Shift: incurrence of cumulative residual deflections undermany axle L/V (NAL) passes

Ø Moving axle loads; vertically loaded and unloaded lateral resistance;thermal loads; curvature and alignment defects

Consulting Services

Influence of Lateral Resistance Track Shift

xo

V

L

V

L

L

Deflection

Res. Defl.


Tack Shift Residual Deflection Mechanism: Moving L/V Loads

xo

δresidual

Consulting Services

Track Shift and Moving Loads

• Net residual deflections are a cumulative sum of axle load passes!


Consulting Services

Lateral Resistance Influence on Track Stability

0 1 2 3Displacement, w (in)


TR

TN

Bucklingregime

Tall

Tbmax

Tbmin

0

500

1000

1500

2000

2500

3000

3500

La

tera

l R

esis

tan

ce

, F

(lb

s) Peak Resistance, FP


WP WL

Track Buckling

Fp (stat)

Unloaded tie

Fe

WeWp


Fp (dyn)

µ • Rv

Loaded tie


Tie load

Track Shift

0 10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Resi

dual d

eflect

ion

(in)


We=0.005 in.

We=0.03 in.

We=0.05 in.

We=0.015 in.

2° concrete tie; 136#;

ÎT=50°F;V=55 kips;

FP=2000lbs; Fe=1500lbs; wp=0.3in; L/V=0.5

0 10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Resi

dual d

eflect

ion (

in)


We=0.005 in.

We=0.03 in.

We=0.05 in.

We=0.015 in.

2° concrete tie; 136#; ÎT=50°F;V=55 kips; FP=2000lbs; Fe=1500lbs; wp=0.3in; L/V=0.5

Elastic Limit Influence


Consulting Services

Lateral Resistance Influence on Track Stability

Key Track Shift Issues

FRA Vehicle/Track Interaction Safety Limits on Track Shift

L/V = 0.4 + 5/V(L/V is net axle ratio)

L66=31.4 kips or (L/V)66= 0.48

(what lateral resistance is required tomeet criterion?)

What is the allowable net axle L/V for high speed passenger operation?

What are the limiting L/V conditions for heavy freight/long train applications?

Current R&D Need

Requires industry driven R&Dprogram to evaluate limiting

conditions/factors


Consulting Services

Conclusions

• Track lateral resistance is an important parameter for track geometry retention and trackstability management

• It is a complex parameter: highly non-linear, variable, difficult to measure, has both static and dynamic components where the tie/ballast friction coefficient plays a key role

• Ballast work (surfacing, lifting, tamping) reduces lateral resistance considerably (40 -70%) requiring quick and efficient restoration HOW TO RESTORE?

• Dynamic track stabilization (DTS) has proven to be a quick and effective means to restore lateral resistance, and typically does not require any speed restrictions.

• Based on US data, traffic (MGT) consolidation for equivalent lateral resistance recovery may require larger than the currently accepted 0.1MGTs. MORE R&D IS REQUIRED FOR EVALUATION!

• Track lateral resistance is a key parameter for both track buckling and track shift evaluations, but each requires different components of the lateral resistance function

Where to?


Consulting Services

Challenges/Research Needs

Key Research Need: quantification of MGT consolidation behavior i.e. tonnage requirements for ballast resistance recovery:

qWhat is the mechanics of ballast compaction under traffic loads?

ØWhat is the influence of axle loads?

ØWhat is the influence of train speeds?

ØWhat is the influence of track types/conditions?(concrete/wood/ tangent/curved)

ØWhat is the influence of reduced resistance on recovery?(initial conditions)

Bottom Line: is the 0.1 MGT adequate? If NOT, what is??


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