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Beddingoptimisationin turnouts
Geometrical discontinuities along turnouts can lead to strong localised variationsof superstructure loads. By using Under Sleeper Pads (USP) with varying stiffness,the bedding conditions can be optimised and as a result the turnout area can besmoothed out.
Harald Loy, System Engineer,
Getzner Werkstoffe GmbH

Modern railway tracks need to beirregularity which can result in various

able to bear the loads from rail vehicles

degrees of rail deflection within different

via the rails, rail seats and sleepers as

areas, even if other boundary conditions

evenly as possible and distribute such toremain unchanged.

the track superstructure and subgrade.

Variations in stiffness along the

By distributing these loads sufficiently,

tongue and frog area, as well as thestresses on the superstructure elements

constantly changing load-bearing surface

can be kept as low as possible, helping

area of the sleepers in the ballast

to minimise maintenance expenses andsuperstructure result in discontinuity ofthus increase the operating life of thethe track system.

track system.
Although one can draw on tried andThe differences in the loaddistributing over the turnout length is atrusted calculation methods, as per

3-dimensional problem which can be

Zimmermann for beams on elastic

grasped and analysed using Finite

foundation in respect of the load

Elements Methods (FEM). By installing

distribution effect, there are limitations

additional elastic elements with definedwhen it comes to turnouts. Due to theirstiffness it is possible to increase the load-geometry alone, turnouts are an

distributing effect of the rails. At the sametime, the load-bearing characteristics ofthe track frame can be optimised. One
cost-effective way of approaching thistarget is to use Under Sleeper Pads (USP)
with varying degrees of stiffness.
The following paragraph describes
the fundamental impact of the bedding
modulus, the possible increase insuperstructure elasticity via USP
and a 3-dimensional FEM turnout

Turnout with rigid crossing frog and check rails

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REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 6 2007

model for optimising the USP arrangement
is provided.

frogs5. The positive experiences with USP

Elements Method (FEM) can help us toBut in order to cut calculation times, thein turnouts have led to the development ofgrasp this system.

individual components are reduced bya standardised design for the Austrian

Using FEM and high-performancebase elements to their relevant

computers, it is possible to generate afunctionality and the necessary degrees

complete turnout with padded sleepersof freedom. Another advantage of theFEM turnout modeland to perform analyses in respect of its

model is that variable parameters can be

It is necessary to understand the entireload-bearing functions. In contrast to theassigned for all geometries and stiffnesses

system in order to be able to transpose theclassic calculation method according toin the rail elements (tongue, crossing frog,

Federal Railways.

check rails, etc.). The same is valid forsleeper parameters and the non-linear
behaviour of the rail fasteners (railplates/baseplates function under pressureloads – fastening clips function undertension loads). Moreover, the behaviour ofthe bedding (sleeper pads and ballast) canbe modelled using any desired non-linear
deflection curves.
As the individual elastic levels are not‘superposed’ by the formation of resultant
spring stiffness, it is possible to simulate adivision of the flexibility in levels aboveand below the sleepers. As a result, it isalso possible to individually observe
deformation variables.
Parameterisation of the model allows
Figure 1: Deflection pattern of the relevant rail through the entire turnout with stepwise and uniformly
reduced bedding modulus

for any standard turnout to be generated
with the defined characteristics and for
calculations to be carried out with apositive experiences gained with padded

Zimmermann, there is no need formoving load collective, corresponding tosleepers to applications involving turnouts.

idealisation by transformation of thethe load impact of the bogies. As a result,

And furthermore to balance out theentire structure (transverse sleepers in

one obtains all of the vertical deformationgeometrically determined differences inlongitudinal sleeper superstructure,in the entire structure (subsidence andvertical load distribution. The Finite

resultant stiffness for several elastic levels).

rises); the strains result from the kinematicconditions and the parameters of theconstruction components. A holistic modelof this nature can be helpful for grasping
the system comprising the elasticallymounted turnout in the ballasted trackand making targeted adjustments for thefurther development of such.

Analysis of load-bearing behaviour
In order to understand the bedding impact
on the vertical rail deflection, the stiffnessof the ballast and the subgrade throughout
the entire turnout area is uniformly andstepwise reduced within the framework ofa simulated calculation. The maximum
rail deflection can therefore be calculated
for each load position, based on the loadcollective for a typical bogie (axle loadFigure 2: Comparison of rail deflection patterns with optimised solution using different USP types
along the turnout

220 kN, 3m spacing). The deflection
patterns presented in Figure 1 represent

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REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 6 2007

Bedding Modulus

upgrading of tracks, as the costs involved

The loads on the track superstructure

for such work are also comparatively low.

stemming from rail traffic mainly depend

With ballasted track, elastic USPs noton the behaviour of the track bed, as wellonly allow for a longer rail bending line,

as the geometry and stiffness

which reduces loads on the ballast, they

characteristics of the track frame. For

also help to prevent contact abrasion as

traditional ballasted track, the elasticity

the top layer of ballast can become

derives primarily from the flexibility of theembedded in the pads. Hard contact
points between the bottom of the sleeper

ballast bed and the subgrade. It is
Concrete sleepers with Sylomer® Under
Sleeper Pads (USP)

generally expressed via the bedding

and the ballast are alleviated and therailtrack mounting is more homogeneous.

modulus C and represents the relationshipThe pads also help to prevent sudden

between the surface pressure and therelated rail deflection.

consideration the load-distributing effectsettling of sleepers due to cavitation3.

in the track and the turnouts. The limiting

Due to stabilisation of the top

factor is generally the maximum

ballast layer, migration of ballast rocks

permissible amount of rail foot tension.

resulting from dynamic forces isshifted to lower layers, which can have ap = pressure between sleeper and ballast[N/mm ]2

y = rail deflection [mm]Increasing superstructure elasticity
with Under Sleeper Pads
USPs are a cost-effective method forbenign effect on the long-term quality ofthe superstructure.
Even under the assumption ofsubsequently increasing the elasticity ofdeclining effectiveness over the lifetime of

In simplified terms, the bedding modulus

the superstructure and reducing wear

the rail, USPs still cannot result in any

indicates how much pressure in [N/mm ]and tear on the ballast. They aredetrimental impact on the track

results in a deflection of 1mm. The

comprised of additional elastic elements

superstructure. In this regard, they can be

bedding modulus of different kinds oflocated between the sleeper and the ballast

seen as fail-safe elements. The track

ballasted track ranges from roughly 0.05

and are today available in a continuous

superstructure will always exhibit more

2N/mm (very soft) to more than 0.40

range of modulus levels fromfavourable characteristics than structure

N/mm3 (very hard) on average, depending

approximately 0.02 N/mm3 to harder than

without any USPs.

on the installation conditions1. For new

0.30 N/mm3 for standard products

rail lines, the higher stiffnesses mainly(determination of bedding modulus as per

adequate adhesion of the pads to theresult from the construction of compacted

BN 918 145 – 01 on a prescribed load

sleepers. One possibility is to glue the pad

substructure and anti-frost layers.

plate with ballast profile2).

to the cured concrete, but the general

3

Moreover, the use of the Dynamic Track

The track frame consisting of the rails

There are numerous ways to ensure

trend in the future shows that the pads are

Stabilizer (DGS) in ballasted track also

and concrete sleepers, which is rigidlyintegrated directly into the sleepers as aresults in consolidation. While measures ofconnected into a load-bearing structure via

part of the manufacturing process. A tight

this kind increase the load-bearing ability

the rail fasteners, can remain unchanged inconnection can be achieved using a plasticof the track bed, at the same time the rail’s

its traditional role. This is also valid formesh, half of which is integrated into thefunction as a load-distributing element issleeper pad and the other half of which

reduced, which can have negative

can be vibrated into the wet concrete oframifications for dynamic effects in wheel-the sleeper.
Tests in Germany have shown thatrail contact and can lead to increased

the use of sleeper pads allows forstresses on the ballast.

significantly improved track behaviour

Higher degrees of bedding stiffness
due to consolidated ballast and subgradesand dynamic vibration behaviour

with greater load-bearing capacity can becompared to traditional ballasted track4.

adjusted by installing elastic elements with

In Austria, turnouts with USP havelower levels of bedding modulus.

already been installed since 2002 andWith regard to the flexibility of themeasurements have shown a reduction ofballasted track, the resulting bedding

vibrations in the 40 Hz-50 Hz frequency

modulus of the standard gauge track

range. Moreover, substantially lessshould be set in a way that sufficient rail
deflection is ensured, which should be
about 1.2-1.5mm, taking into

subsidence was found in turnouts with
FEM turnout model for the optimisation ofUnder Sleeper Pads (USP)

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rigid crossing frogs, even compared toconstructions with moveable crossing

the envelope for the maximum verticalbe smoothed out by the installation ofUsing a turnout model based on thedeformations of the relevant rail.

various USPs, in the event of identical

Finite Element Method, it is possible toinitial levels. This allows for a more

analyse the load-bearing behaviour of thelowering of the bedding modulus results inhomogenous pattern of deflection to beconstruction. As data can be varied for

an increase in rail deflection as desired.

achieved (using different USP types). Thedifferent parameters, it is possible to

But at the same time, the various

turnout is smoothed in its function as aanalyse a very wide range of geometricdifferences in the stiffness can also be seen

load-bearing element.

boundary conditions and stiffness

From the curves, one can see that aFigure 3 shows the reduction of rail

conditions. The challenge involved is todifferences in the deformation curves areseat forces compared to a turnout without

take into consideration the non-linear

magnified. The lower the bedding

USP. Even with the relatively stiff pads

bedding properties.

modulus is – the more pronounced

used in this case (> 0.2 N/mm ) the forces

Using the FEM turnout model, an

the differences are. In this regard,transmitted into the superstructure can be

optimised arrangement of Sylomer® USP

along the path of the turnout. The

3

can be calculated for any situation.

References
1. Eisenmann, J. und Rump, R.: Ein
Schotteroberbau für hohe
Geschwindigkeiten. ETR –Eisenbahntechnische Rundschau 46,(1997), Heft 3, S.99…108.
2. DB Systemtechnik: BN 918145-01:
Technische Lieferbedingungen –Spannbetonschwellen mit elastischerSohle – Elastische Schwellensohlen,(Jan. 2004)
3. Müller-Boruttau, F., Kleinert, U.:
Figure 3: Reduction of rail seats forces along the turnout with optimised USP solution

Betonschwellen mit elastischer Sohle,
ETR 50 (2001). H3 S. 90-98.
4. Leykauf, G., Stahl, W.:

the amount of deflection is lowest in the

reduced on the order of 10% to 30%,

Untersuchungen und Erfahrungen mit

crossing frog due to the higher level of rail

depending on the part of the turnout.

besohlten Schwellen. EI Der
Eisenbahningenieur (55) 6/2004,stiffness and the large surface area of thesleepers, whereas immediately after theSummary

last long sleeper.

The use of USPs can increase the elasticity

S. 8-16.
5. Schilder, R.: USP Under Sleeper Pads –By optimising the arrangement ofof track superstructure with relatively low

Ein Bericht über bisherige

USPs with varying degrees of stiffness,investment costs. At the same time, theErfahrungen, ÖVG Salzburg

these differences can be smoothed out.

ballast which is a latent source of track

Congress, Band 65, Sept. 2004

Figure 2 shows a comparison with an

instability is stabilised, as individual

improved arrangement of stiffnesses using

ballast rocks can become embedded in thevarious types of USP.

surface layer of the USP. Loads on theThe first curve shows as an example ofsuperstructure are reduced by a more

the deflection curve without any

homogenous mounting of the sleepers andadditional USPs. The rail deflection of

track stability is improved.

0.8mm in the regular track resultsMoreover, in turnouts, theexclusively from the defined bedding

geometrically determined differences

modulus of the ballast and subgrade ofin stiffness can be smoothed out.

biography

0.2 N/mm . If the vertical deformation

To achieve this target, USPs with various

is increased by the uniform installation ofdegrees of stiffness can be used, positioned

Harald Loy

additional USPs, the resulting bedding

in a way that the entire construction

modulus of roughly 0.10 N/mm3 leads

features improved load-bearing conditions.

to an increase in deflection to 1.3mm

Track irregularities resulting from turnouts

before and after the turnout. The

can thus be mitigated and vibrations canHarald Loy has a degree in civil engineering
after studying at the Technical University ofMunich. He has been employed as System
Engineer since 2005 at Getzner WerkstoffeGmbH in Austria, specialising in railway
track applications.

differences in vertical rail deflection canbe reduced.

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REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 6 2007

Paths are createdby us treading them(Hans Kudszus)

Thanks to its superior materials, Getzner is a technology leader in oscillation and vibration insulation.
We create bespoke, quality, sustainable solutions forand in cooperation with our customers.
Our materials are known for their outstanding properties, durability and resource-efficient production
methods.

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Phone +43-5552-201-0
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