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01 2019

EXPERTISE| OPINION | INTELLIGENCE

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Insulated rail joints:
A solution to improve lifetimeand performance at highmaintenance track sections
Signalling systems are part of every modern rail network. These systems
create a safe and efficient operation by employing the rail as an electricalconduit for train location. To accomplish this, insulated rail joints (IRJs) areused to create blocks or independent sections of track by electrical isolation.
Shortened IRJ life often occurs due to the different static and dynamic
behaviour of IRJs compared to continuous rail. Consequently, many problems
with track deterioration and signalling malfunction are related to them1.
Martin Quirchmair (Getzner Werkstoffe), Erik Frohberg (BNSF Railway) andHarald Loy (Getzner) explain further.
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GLOBAL RAILWAY REVIEW | Volume 25, Issue 01

reduce these losses is to work on tailored solutions
to keep the track quality on a high level over timeand consequently increase the service life of all
IRJ components.

Long-term performance due toenhanced track design

Under sleeper pads (USPs) are well known for
their potential to enhance track design in highmaintenance track sections like turnouts ortransition zones. A diversified portfolio of stiffness
and other mechanical properties makes USPsa viable solution to modify the static and dynamic
bedding modulus of the track, which in turn helps
to reduce settlement and ballast fouling. USPs canbe installed within the concrete sleeper production
process as well as on already finished sleepers.
This flexibility makes USPs suitable for new
installations as well as retrofitting.
Due to these positive characteristics, USPs
should be considered to improve the long-term
performance of IRJs.

Model-based design

A singularity within the track

Ideally the static and dynamic behaviour ofa railway superstructure is homogeneous within
the entire network. Every change in bedding
stiffness leads to impacts and accelerated
deterioration. Unfortunately, local stiffness changes
are unavoidable due to the need of special track
work and signalling systems.
IRJs are essential for railway operation andsafety, and therefore are used on signalised
high-density main lines. To achieve electricalisolation, prefabricated bonded IRJs are used andwelded in track. Various materials such as epoxyand Kevlar are used to create this insulation,
as shown in Figure 1.
Increased dynamic forces at IRJs and theirimmediate vicinity are the most important cause of
IRJ failure. Impacts from wheels lead to increased
metal flow at the rail ends (short circuit), end-post
battering and degradation of ballast. Furthermore,increased IRJ deflection as a result of fouled ballast
induces stress onto IRJ components2.
On high-tonnage routes, IRJs may be replaced
within as little as 12 to 18 months, whichsignificantly reduces the availability of the track3
and increases operational costs. One approach to@GlobalRailway

Issues at IRJs have been a topic on and off
in the past. At a meeting between BNSF Railway(the operator of one of the largest rail freight
networks in North America) and Getzner USA
Inc. in early 2016, an opportunity was identified
as a way to study this sensitive area of track.
Current practice at BNSF Railway has been toinstall wooden sleepers under IRJs in concrete
sleeper territory. However, this practice does notcreate a homogeneous sleeper type.
Two IRJ concrete sleeper panels were scheduled
to be installed in autumn 2016 which could beequipped with USPs. To figure out the best typeof USP to be used for this special application,a custom-built finite element method (FEM) model
was used.
Many analytical track models calculate
rail deflection and other important design
parameters by using the Zimmermann
method – which idealises the track as an
infinitely-long, continuously-bedded beam.
These models work very well in homogeneousenvironments, where track parameters remainunchanged. This has been verified repeatedly.
In areas with suddenly altering properties
the Zimmermann method reaches its limit as thedifferential equations cannot be solved analyticallyanymore. The solution to this problem can be foundin numerical models like FEM. FEM subdivides themodel into a finite number of elements and solves
their differential equations numerically. As a result,complex track sections, such as special track
work, can be analysed as a system for a holistic
design approach.

MARTIN QUIRCHMAIR
has been working with
Getzner Werkstoffe formore than six years. He ispart of the R&D Department
where he studies dynamic
behaviour and damping
characteristics of elastomers
in railway superstructures,
including development ofsimulation models andon-site measurements.
Between 2015 and 2017,
Martin was responsible forthe North American railway
market of Getzner USA Inc.
Martin holds a Master’s
degree in Physics fromthe Technical Universityof Vienna (TU Wien).

ERIK FROHBERG has
a 30-year engineering
career with BNSF Railway,
where he has held various
positions of increasing
responsibility in track andstructures departments.
Starting his career as an
Assistant Roadmasterwith the former Burlington
Northern in Lincoln, NE,
Erik is currently the Directorof Track Standards andProcedures. He graduatedfrom North Dakota State
University where he receiveda Bachelor of Science in CivilEngineering. He is a memberof AREMA Committees 5 and30 and also of the RTA.

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INFRASTRUCTURE

RIGHT: Principalof IRJ: Rail-ends
are electricallyinsulated and bondedwith fishplates
and adhesives

FIGURE 1

RIGHT: Calculated
stress in IRJ
panel for centre
loading condition

FIGURE 2

The IRJ approach

HARALD LOY is Head of R&D
in the Railway Division atGetzner. He graduated fromthe Technical University ofMunich in Civil Engineeringand holds a Doctoral degreein Railway Engineering fromthe University of Innsbruck.
After being employed in thecomputer industry, he hasbeen working as a System
Engineer since 2005,
focusing on simulation,
laboratory testing andin-situ measurements ofelastic track applications.
Furthermore, Harald works
as a Postdoctoral Researcher
at the Intelligent Transport
Systems Unit within theUniversity of Innsbruck.

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Looking at the situation of an IRJ in particular,
the singularity is found mainly at the IRJ itself.
Differences in stiffness and mass ratio lead toextensive wear on all track components over time.
In the beginning the characteristic behaviour of
the IRJ is dominated by its properties, whereas
after some time in revenue service the behaviour
gets dominated by continuously increasing
track defects, such as hanging sleepers andfouled ballast.
This problem can be tackled on two fronts.
Firstly, reduction of inhomogeneity by decreasing
ballast contact pressure and dynamic loads to limit
wear of all track components. And secondly, thestabilisation of ballast to reduce ballast movement
and improve long-term performance.
Elasto-plastic USPs are able to handle bothof these issues. The FEM calculation showsthat static forces at a newly-installed IRJ and its
immediate vicinity are reduced by roughly a quarter.
Nonetheless, the biggest benefit can be found in thedynamic interaction between ballast and bottomof the sleeper. Unpadded sleepers show a ballast
contact area of three to five per cent. This contact

area can be increased to values up to 35 per centand more, depending on the USP model4.
After taking all different properties of the new IRJ
and USPs into account, the FEM calculation showsthat the ballast contact pressure can be reduced by
70-90 per cent.
Additionally, the top layer of the ballast getsstabilised due to strong interlocking between
ballast and USP. Lateral track resistance isincreased. Ballast movement and surface
irregularities are for the most part eliminated.

Validation in the field

The true test of a new technical innovation isfield implementation. Engineers do their very
best to find the optimum computational design,
but performance in track determines if a solutiondelivers on its promises. Ballast and subsoil
conditions can never be predicted perfectly, andsome uncertainty is left in every calculation.
After more than a year of revenue service,measurements at the padded IRJ panels weretaken. On this corridor BNSF Railway runs trains
with 36 short tonnes (33 metric tonnes) axle loadand speeds of roughly 60mph (100km/h).
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FIGURE 3

LEFT: BNSF Railwayruns 36tn. sh. (33t)axle load heavy-haultrains on its PowderRiver Division Track near
Omaha, NE, U.S.

FIGURE 4

LEFT: Rail deflection
was measured at four
locations close tothe IRJ. Right: Moreuniform rail deflectionof padded IRJ (○)
vs. non-padded IRJ (□)
in immediate IRJ vicinity
leads to extended
long-term performance

Nearby, a standard IRJ with no USPs was selected
for reference. At the control location trains withsimilar axle loads, speeds and frequency areoperating. The setup chosen for this measurement
had a focus on rail deflection.
Information about deflection during train
operation is needed to achieve a fundamental
understanding of the IRJ behaviour. With thesefindings the model can be refined for future
calculations and the quality of the solution
increases accordingly. Rail deflection was measured
at four different locations.

Evaluation and results

Due to the different configuration of each train theevaluation is based on the locomotives, which show
similar axle loads for all measured trains.
In order to obtain statistically significant
results for every single sensor, an average of themaximum deflection of the first three axles of
all trains was made. This way the benefit of thesolution in terms of stiffness adjustment can beseen in Figure 4.
The IRJs perform differently than the adjacent
track. However, the IRJ itself shows less deflection
with USPs compared to the control location.
This phenomenon can be explained by looking
at track alignment and surface over time. USPs
@GlobalRailway

are well known to reduce ballast movement andfurthermore preserve track surface. Developmentof track defects is prevented and consequently
the deflection at the IRJ location remains steadyover time.

Conclusion

IRJs violate the homogeneity of railway tracks,
which results in high dynamic stress andsubsequent IRJ failure.
In 2016, BNSF Railway decided to test a new
remedy for this high maintenance track section
by installing IRJ concrete sleeper panels equippedwith elasto-plastic polyurethane USPs. Getzner
Werkstoffe’s expertise in designed elasticity forspecial track work provided tailored USPs basedon modern FEM simulations.
The benefits of this solution regarding
long-term track alignment were validated byin-field measurements in a heavy-haul track ofBNSF Railway in Nebraska, U.S.
IRJ concrete sleeper panels equipped withelasto-plastic polyurethane USPs show a more
uniform rail deflection compared to standard
IRJs panels. Stress within the IRJ and roadbed
is reduced, which leads to less maintenance,
higher track availability and a more cost
efficient operation.

REFERENCES
1.

A. Wahnström: ‘Validationof insulated joints’; Chalmers
University of Technology; 2011

2.

M Akhtar, D. Davis, T. O’Connor:‘Revenue service evaluation ofadvanced design insulated joints’;
AREMA 2008 Annual Conference,
Salt Lake City, Utah, USA; 20083.

D. Davis, M. Akhtar, E. Kohake,
K. Horiszny: ‘Effects of heavy
axle loads on bonded insulated
joint performance’; AREMA 2005
Annual Conference, Chicago,IL; 2005

4.

H. Loy, A. Augustin; ‘Pushing thelimits of ballasted heavy-haulrailway track by means ofhigh-strength under-sleeper
pads made of a speciallydeveloped PUR’; Rail Engineering
International; 201561