TRAVERSE DE CHEMIN DE FER

SLEEPER FOR RAILWAY TRACKS

Abrégé français

Traverse (12) destinée à un chemin de fer constitué de rails reposant sur un lit de ballast (10). Ladite traverse possède sur sa face inférieure un revêtement (22) en plastique déformable qui entraîne une meilleure stabilité d'appui du rail et réduit parallèlement les dommages subis par le lit de ballast.

Abrégé anglais

The invention relates to a railway sleeper
(12) consisting of rails placed on top of a bed
of road metal. The underside of said sleeper is
provided with a plastic deformable coating (22)
increasing the stability of the track layer and
reducing damage to the bed of road metal.

Revendications

7
Claims
1. Sleeper for railway tracks made of one of concrete,
reinforced concrete and steel, and resting on ballast,
having a plastically deformable coating on an underside
thereof.
2. The sleeper according to claim 1, the plastically
deformable coating being attached exclusively in a region
of supports of said sleeper.
3. The sleeper according to any one of claims 1 and 2,
the coating comprising a tar/asphalt mixture.
4. The sleeper according to any one of claims 1 and 2,
the coating comprising a plastic.
5. The sleeper according to any one of claims 1 and 2,
the coating comprising one of wood, wood-concrete, and
wood chips.
6. The sleeper according to any one of claims 1 to 5, an
underside of the coating being profiled.
7. The sleeper according to any one of claims 1 to 6,
the coating being constructed as a coating applied in a
process for producing the sleeper.
8. Railway track with a bed of ballast and a track grid
which rests on the bed of ballast, comprising sleepers
according to any one of claims 1 to 7.

Description

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Sleeper for railway tracks
The invention relates to a sleeper for railways tracks
which is made of concrete, reinforced concrete or steel and
is of the kind which is used in the permanent way in
connection with track grids resting on a bed of ballast.
As a structural element within the permanent way, the
sleeper absorbs the forces emanating from the rolling loads
via the rails and the intermediate layers with the aid of
the bracing elements in the supporting points of the
sleeper supports, and the forces introduced are conducted
away, in a load-distributing manner, to the ballast
structure lying underneath the said supports, and are
passed on to the foundation or subsoil.
Wooden sleepers have been used as sleepers since the
beginning of the railway age last century. During the
period of industrialisation and as a barometer of the steel
industry, steel sleepers were also produced and installed,
including, more recently, ones in the form of "Y-sleepers".
Since the 1950's, use has increasingly been made of
prestressed concrete sleepers, which have currently
prevailed as the state of the art.
The wooden sleeper, which is hardly used any more for,
among others, ecological reasons had the advantage, inter
alia, of being regarded as "elastic". One of the reasons
for this is the interlinking of the comparatively soft
underside of the wooden sleeper with the hard stone
ballast.
As opposed to this, the concrete sleeper, and the steel
sleeper which is comparable in this connection, have the
disadvantage that, in contrast to the wooden sleeper, two
inelastic materials meet at the support face of the beam on
the ballast, so that the abovementioned interlinking is not

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possible and therefore the absorption of longitudinal and
transverse forces by the bed of ballast is diminished.
Furthermore, the hard, inelastic points of contact between
ballast and sleeper lead to damage or destruction of the
sleeper or ballast in the event of excessive stressing.
In order to avoid excessive stressing of the ballast, in
particular on high-speed stretches, it has already been
proposed that the underside of the sleeper be coated with
an elastic polymeric material in order to achieve shock-
absorption and thereby relieve the compressive load on the
ballast. It is true that the bed of ballast can be
preserved by using an elastic intermediate layer of this
kind between the ballast and the concrete sleeper, but on
the other hand the forces resisting longitudinal and
transverse displacement are lowered considerably as a
result of this, so that the positional stability of such
tracks is still lower than that of tracks in which the
concrete sleepers rest directly on the bed of ballast.
The underlying aim of the invention is therefore primarily
to provide a sleeper with the aid of which the positional
stability of the track can be increased and, at the same
time, damage to the bed of ballast is avoided.
This object is achieved, according to the invention,
through the fact that the sleeper is provided on its
underside, particularly in the region of its supports, with
a plastically deformable coating.
By reason of the plastically deformable coating of the
underside of the sleeper, "interlinking" of the sleeper
with the ballast is achieved because of the plastic
deformation of the coating, as a result of which, for one
thing, the resistance of the track grid to transverse
displacement and to longitudinal displacement is
appreciably increased and the positional stability of the

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track is thereby substantially improved. What is also
achieved as a result of this is that, on the one hand, peak
pressures are reduced and edge pressures lessened and, on
the other hand, that the area of contact between ballast
and sleeper is enlarged, so that the pressures per unit of
area are diminished, compared with the prior art, and the
destruction of material is reduced or precluded. Finally,
the "softness" of the region of contact between ballast and
sleeper which is achieved with the aid of the coating is
also material-preserving.
In a preferred further development of the invention, the
plastically deformable coating may substantially consist of
a tar/asphalt mixture, which is a particularly cost-
effective solution. Alternatively, the coating may
substantially consist of a plastic, of wood-concrete, of
wood or of wood chips.
Merely for reasons of cost, it may be expedient to
construct the plastically deformable coating exclusively in
the region of the support of the sleepers, so that the
areas which are devoid of supports are left uncoated.
The thickness of the coating may be comparatively low, that
is to say less than 10 mm, and may, in particular, amount
to about 5 mm. Furthermore, the underside of the coating
may be profiled, in order to achieve still better anchoring
of the sleepers on the bed of ballast.
Although the sleeper coating according to the invention
may, optionally, also be attached to the sleepers at a
later stage, it is preferable to integrate the application
of the coating into the process for producing the concrete
sleepers, in order to ensure the best possible bond. To
this end, the coating may be applied to the corresponding
regions of the underside of the sleeper, particularly as
the final working operation in the casting of the sleeper.

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Alternatively, the coating could also be stuck to the
underside of the sleeper at a later stage.
An exemplified embodiment of the invention will be
explained in greater detail below with the aid of the
drawings, in which:
figure 1 shows a vertical section through a track, in a
plane parallel to the rails,
figure 2 shows a plan view of the track according to
figure 1,
figure 3 shows a horizontal section through the track
according to figure 1, perpendicular to the
longitudinal direction of the rails, and
figure 4 shows an enlarged sectional view in the region of
a sleeper.
In the figures, the reference numeral 10 designates a bed
of ballast, the reference numeral 12, sleepers disposed in
the said bed of ballast, the reference numeral 14, rails
disposed on the said sleepers, and the reference numeral
16, a wheel which is guided on the said rails. The
conventional intermediate layers 18 are disposed between
the rail 14 and the sleepers 12. The bed of ballast 10
lies on a track formation 20. So far, this structure of a
railway track corresponds to the conventional structure and
requires no further explanation.
Plastically deformable coatings 22 are constructed on the
undersides of the sleepers 12, that is to say, as can be
seen from figures 2 and 3, in such a way that those regions
24 of the sleepers 12 which are devoid of supports are
devoid of the coating. It should be noted that the hatched
areas in figure 2 are intended to distinguish those regions

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of the underside of the sleeper (not visible in figure 2)
on which a coating is provided. The arrows 26 and 28 in
figures 1 to 3 are intended to indicate, respectively, the
transverse and longitudinal forces occurring in the track.
The detail representation according to figure 4 illustrates
the interlinking of the stones of the bed of ballast with
the plastically deformable coating 22. For one thing, it
immediately becomes clear from this that the displacing
forces become distinctly greater because of the
interlinking, and for another, it can readily be seen that
the area of contact of the underside of the sleeper with
the bed of ballast is now greatly enlarged, so that the
forces occurring between the contact areas per unit of area
are, as a whole, distinctly reduced.
The advantages achieved with the aid of the invention
therefore lie, in particular, in the fact that
- the transmission of force between sleeper and
ballast now occurs over an area instead of at
certain points, as in the case of the prior art,
- peak pressures on individual ballast stones are
reduced and the edge pressures lessened,
- fragmentation of the ballast stones and damage to
the concrete sleeper is thereby avoided, and
- because of the interlinking of the bed of ballast
at the plastically deformable coating of the
sleepers, an increase in the resistances to
longitudinal and transverse displacement occurs,
which improves the positional stability of the
track.

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List of reference symbols
bed of ballast
12 sleepers
14 rails
16 wheel
18 intermediate layer
track formation
22 coating
24 regions devoid of supports
26 transverse forces
28 longitudinal forces

Dessin représentatif