www.trackandsignal.com
August–October 2019VOLUME23NUMBER

3NEW ZEALAND
GWAIROA–NAPIER LINE REOPENEDCONFERENCE CONFIDENTAUCKLAND TUNNEL COMPLETEDUNEDIN’S HISTORICSTATION FLOURISHINGGGGBUDGET SHARERAIL PROJECTS PROMINENT IN
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Improving thelifespan ofinsulated joints
Even in highly modernised railway tracks a considerable portion of signalling systems work by utilising
the rail as an electrical conductor. To ensure safe and efﬁcient operation, the rail needs to be separated
into independent circuits to allow trains to be located within deﬁned sections. Insulated rail joints (IRJs)
are still the main tool used to accomplish this separation but usually require high maintenance efforts.
The different static and dynamic behaviour of IRJs compared to continuous rail leads to signiﬁcantly
shortened IRJ life and, furthermore, to increased track deterioration and signalling malfunctions. Theuse of tailor-made under-sleeper pads (USPs) with designed stiffness in IRJ sections shows promising
results in terms of maintenance reduction and improved service life and helps to reduce overall
operational costs. MARTIN QUIRCHMAIR (R&D railway division at Getzner Werkstoffe), HARALD LOY(head of R&D railway division at Getzner, postdoc at the Intelligent Transport Systems Unit, Universityof Innsbruck) and CLEMENS BELL (area sales manager for Asia Paciﬁc at Getzner Werkstoffe) explain
further.

I

deally, the static and dynamic behaviour of a railway superstructure ishomogeneous within the entire network. Every change in bedding stiffness
leads to impacts and accelerated deterioration. Unfortunately, local stiffnesschanges are unavoidable due to theneed of special trackwork and signallingsystems.
IRJs are essential for safe railway
operation and therefore are used on
signalised high-density mainlines. To
achieve electrical isolation, prefabricated bonded IRJs are used and welded intrack. Various materials such as epoxyand Kevlar are used to create this insulation (see Figure 1).
Increased dynamic forces at IRJs andtheir immediate vicinity are the maincause of IRJ failure (see Figure 2). Impacts from wheels lead to increased
metal flow at the rail ends (short-circuit), end post battering and degradation of ballast. Furthermore, increased+ FIGURE 2 Failure propagation of anIRJ defectIRJ deflection as a result of fouled ballast induces stress into IRJ components.
On high-tonnage heavy-haul routes,IRJs may be replaced within as little as12–18 months, which reduces the availability of the track significantly and increases overall operational costs. Oneapproach to reduce these losses is towork 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
to enhanced track design+ FIGURE 1 Principal of IRJ: rail ends
are electrically insulated and bondedwith fishplates and adhesives

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Under-sleeper pads (USPs) are wellknown for their potential to enhance
track design in high-maintenance track
sections like turnouts or transition
zones. A diversified portfolio of stiffness
and other mechanical properties makes
USPs a viable solution to modify thestatic and dynamic bedding modulus ofthe track, which in turn helps to reduce

Track+Signal August–October 2019settlement and ballast fouling. USPs canbe installed within the concrete sleeper
production process as well as on existing sleepers. This flexibility makes USPs
suitable for new installations as well as
retrofitting.
Due to these beneficial properties,
USPs should be considered to improve
the long-term performance of IRJs.

Model-based design
Issues at IRJs have been a topic on andoff in the past. At a meeting in early 2016
between one of the largest railway operators in North America and Getzner
USA Inc, an opportunity was identified
as way to study this sensitive area oftrack. Common practice at this North
American heavy-haul operator has been
to install wood sleepers under IRJs in
concrete sleeper track sections. However, this practice does not create a homogeneous sleeper type.
Two IRJ concrete sleeper panels weregoing to be installed in autumn 2016
which could be equipped with USPs. To
determine the best type of 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 bed-

TRACKING+ FIGURE 3 Calculated stress in IRJ
panel for centre loading condition+ FIGURE 4 Thirty-three-tonne-axleload heavy-haul trains operate on thistrack section in North America.
ded beam. These models work very wellin homogeneous environments wheretrack parameters remain unchanged.
This has been verified repeatedly.
In areas with suddenly altering properties, the Zimmermann method reaches
its limit as the differential equations
cannot be solved analytically any more.
The solution to this problem can befound in numerical models like FEM.
FEM subdivides the model into a finite
number of elements and solves their differential equations numerically. As a result, complex track sections like special
trackwork can be analysed as a system
for a holistic design approach.

The IRJ approach
Looking at the situation of an IRJ in particular, the singularity is found mainly
at the IRJ itself. The difference in stiffness and mass ratio leads to extensive
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 inrevenue service the behaviour becomesdominated by continuously increasing
track defects like hanging sleepers andfouled ballast.

This problem can be approached on
two fronts: firstly, reduction of inhomogeneity by decreasing ballast contactpressure and dynamic loads to limit
wear of all track components and, secondly, stabilisation of ballast to reduceballast movement and improve longterm performance.
Elasto-plastic USPs are able to handle
both of these issues. The FEM calculation shows that static forces at a newly
installed IRJ and its immediate vicinity
are reduced by roughly a quarter.
Nonetheless, the biggest benefit can befound in the intersection between ballast and the bottom of the sleeper. Unpadded sleepers show a ballast contact
area of 3–5 per cent. This contact area
can be increased to values up to 35pc
and more, depending on the USP model.
After taking all different properties of
the new IRJ and USPs into account, theFEM calculation shows that the ballast
contact pressure can be reduced by70–90pc.
Additionally, the top layer of the ballast is stabilised due to strong interlocking between the ballast and USP. Lateral
track resistance is increased. Ballast
movement and surface irregularities
are, for the most, part eliminated.

Validation in the ﬁeld
The true test of a new technical innovation is field implementation. Engineers
do their very best to find the optimum
computational design but performancein track determines if a solution deliverson its promises. Ballast and subsoil conditions can never be precisely predictedleaving some uncertainty in every calculation.
The test section selected has operating
trains of 33t axle loads and speeds of approximately 100kmh). Measurements of
the IRJ fitted with USP were taken after
more than one year of revenue service.
Nearby, a standard IRJ with no USPs
was selected for reference. At thecontrol location trains operate with sim-+ FIGURE 5 LEFT Rail deﬂection was measured at four locations close to theIRJ. RIGHT More uniform rail deﬂection of padded IRJ (○) versus non-padded
IRJ (□) in the immediate IRJ vicinity leads to extended long-term performance.

ilar axle loads, speeds and frequency.
The set-up chosen for this measurement had a focus on rail deflection.
Deflection data during train operationis needed to achieve a fundamental understanding of the IRJ behaviour. With
these findings the model can be refinedfor future calculations and the quality ofthe solution improves accordingly.
Rail deflection was measured at four
different locations.

Evaluation and results
Due to the different configuration ofeach train the evaluation is based on thelocomotives, which show similar axle
loads for all measured trains.
In order to obtain statistically significant results for every single sensor an
average of the maximum deflection of
the first three axles of all trains wasused. This way the benefit of the solution in terms of stiffness adjustment canbe seen in Figure 5.
The IRJs perform differently to theadjacent track. However, the IRJ itself
shows less deflection with USPs compared to the control location. This phenomenon can be explained by looking attrack alignment and surface over time.
USPs are well known to reduce ballast
movement and, furthermore, increase
track stability. The development of
track defects is prevented and, as a consequence, the deflection at the IRJ location remains constant over time.

Conclusion
IRJs violate the homogeneity of railway
tracks, which results in high dynamic
stress and subsequently in IRJ failure.
In 2016 one of the largest heavy haul
railway operators in North American decided to test a new solution for this highmaintenance track section by installing
IRJ concrete sleeper panels equippedwith elasto-plastic polyurethane USPs.
Getzner Werkstoffe used its expertise to
design elasticity for special trackwork
and provided tailored USPs based onmodern FEM simulations.
The benefits of this solution regarding long-term track alignment were validated by in-field measurements in oneof the largest heavy-haul networks inNorth America.
IRJ concrete sleeper panels equippedwith elasto-plastic polyurethane USPs
show a more uniform rail deflection
compared to standard IRJs panels.
Stress within the IRJ and ballast is reduced, which leads to less maintenance,
higher track availability and a morecost-efficient operation.
T+S

Track+Signal August–October 201967