GB2582779A

GB2582779A - Railway sleeper

Info

Publication number: GB2582779A
Application number: GB1904609.3A
Authority: GB
Inventors: James Whiteley Christopher
Original assignee: Oxford Plastic Systems Ltd
Current assignee: Oxford Plastic Systems Ltd
Priority date: 2019-04-02
Filing date: 2019-04-02
Publication date: 2020-10-07
Also published as: GB201904609D0

Abstract

A railway sleeper 100 extending longitudinally from a first end to a second end, the sleeper comprising a support structure 30 extending longitudinally between the first and second ends, the support structure comprising a first material; and comprises along at least part of its longitudinal extent between the first and second ends a core 40 comprising a second material 42 providing a core body that can be engaged by a fastener 62 to be provided thereby reducing a direct transfer of pull-out forces from the fastener 62 onto the support surface 30. Additionally, a method for manufacturing a sleeper 100 comprises the steps of forming the support structure 30 by pultrusion, the support structure defining a cavity (40, figure 3) therein; forming a core material 42; placing the core material inside the cavity; moulding an outer structure around the support structure to seal the cavity or placing the core material inside the cavity, leaving an open end of the sleeper that is to be sealed by an end cap (22, figure 3) once the core material is placed in the cavity.

Description

Railway sleeper

Field of the Invention

This invention relates to a railway sleeper, in particular a railway sleeper made of plastics material.

Background

A railway sleeper extends transversely underneath a pair of rails, which are attached to the sleeper by appropriate rail baseplates, clips and screws. The sleeper rests on a bed of ballast. Traditionally, railway sleepers have been made of timber or reinforced concrete, but more recently sleepers have been constructed from other materials such as steel and plastic materials. United States Patent 6604689 discloses a steel sleeper.

GB2473729 discloses a railway sleeper in the form of an elongate member of plastics material. GB2495763 discloses a railway sleeper of a composite plastics material, which may be formed from recycled materials. GB2554718 discloses a plastic railway sleeper comprising an inner support structure.

An object of the present invention is to provide a railway sleeper of improved construction.

Summary of the Invention

According to a first aspect of the present invention, there is provided a railway sleeper as defined by claim 1, which extends longitudinally from a first end to a second end, the sleeper comprising a support structure extending longitudinally between the first and second ends of the sleeper, the support structure comprising a first material, wherein the support structure comprises along at least part of its longitudinal extent a core comprising a second material providing a core body that can be engaged by a fastener to be provided thereby reducing a direct transfer of pull-out forces from the fastener onto to support structure.

The support structure provides a structural backbone to the railway sleeper. However, materials which are suitable to provide such structural support or reinforcement thereof generally may be relatively brittle when subjected to a local load and inelastic. By providing a core body, a fastener can engage primarily in the core body rather than having to rely on an engagement in the support structure.

As will be explained below, the present invention provides a possibility to engage a fastener in the core body while avoiding direct contact between the fastener (or fastener shaft) with the support structure. Thereby, most if not the entirety of any pullout forces that may be applied to the fastener can be transferred onto the core body, rather than directly to the support structure. If pull-out forces are transferred from the core body onto the support structure, these are distributed over a larger area than a direct transfer from a fastener. This allows the support structure to be manufactured from a more rigid material than would otherwise be tolerable.

In the present invention, an undesirable direct transfer of pull-out forces from the fastening means onto the support structure is less likely and practically prevented by providing a core body. The core body may be understood as a distinct structure.

When fastening means (such as a screw, nail or hook, for example) are inserted into the sleeper, in order to affix rails to the sleeper, a bore will be formed through the support structure, wherein a hole may have been pre-drilled, prior to insertion of the fastener, and/or the fastener may be self-tapping. By providing a core body, the material properties can be designed to be better suited for retaining a fastener.

The second material (core material) may comprise material designed to offer higher screw retention properties than the support structure. For instance, the second material may comprise a fibre reinforced polymer, such as reinforced polyurethane.

The support structure may be formed from metal, such as steel. This may be formed by any suitable technique, such as hot rolling, cold rolling or extrusion. In embodiments, the support structure is formed from a synthetic material, such as a plastics material, such as a composite combined with reinforcement such as glass reinforcement and formed by any suitable technique, such as moulding, extrusion or pultrusion. In some embodiments, the support structure comprises a resin, such as vinyl ester, polyester, epoxy or polyurethane combined with a fibre reinforcement. In embodiments, the support structure can be understood as a polymer matrix, reinforced with elongate fibres, generally unidirectionally aligned with a pultrusion axis to provide strength to the support structure. Embedded within composite material (e.g. the matrix) are reinforcing fibres. The fibres may be embedded, for instance, during the moulding of the body, for instance by placing fibre or fibre mats in appropriate locations. The fibres may be embedded by coextruding fibres with the body. The fibres are of generally elongate structure to impart strength and stiffness to the body, whereby it is believed that the strength and stiffness of the body increases generally with the length and volume fraction of the fibres.

Preferably the fibres extend along an elongate extension between the first and second ends, although it will be understood that fibres due to their nature and manufacturing method may be shorter and not perfectly aligned with the elongate extension. Likewise, as fibres are embedded or co-extruded, there may be occasional misalignment or bending of fibres, or the fibres may be intentionally meandering to a certain degree. However, it will be understood that the fibres oriented along the elongate extension are purposefully placed such that a large proportion of the fibres, e.g. more than a quarter, or more than half, is generally aligned with the elongate extension. As a simplified illustration, the fibres can be understood as generally unidirectionally aligned with the elongate extension (which may be a pultrusion axis) to provide strength to the body, such that the majority of the fibres are oriented in the elongate extension of the railway sleeper.

The core body may comprise a polymer reinforced with fibres that are shorter than the elongate fibres of the support structure, such that these are more prone to arrange anisotropically, or randomly, and thereby are better suited for engaging a fastener such as a screw, bolt or nail. The first and the second material may therefore be distinguished by the length of the reinforcing fibres. The first material, of the support structure, comprises longer fibres tending to align with the extrusion direction and providing rigidity. The second material, of the core, may comprise shorter fibres tending not to align and providing better grip for a fastening means such as a screw.

Likewise, the second material may comprise no reinforcing fibres, or only a negligible amount thereof.

The volume fraction of elongate fibres in the matrix of the support structure may be higher than 35, 40, 45, 50, 55 or 60 volume percent. The structural stability of the sleeper increases the higher the volume fraction is.

The volume fraction of elongate fibres in the matrix of the support structure may be no more than 80, 75, 70, 65 or 60 volume percent. The remainder of the volume may be predominantly matrix resin. This improves the ability to form the support structure.

In some embodiments, the support structure defines a cavity therein, the cavity extending longitudinally between at least a portion of the first and second ends, wherein the second material is provided in the cavity.

The support structure may be provided with a cavity to receive the core material. For instance, a cavity may be provided by way of a hollow extrusion profile. The cavity may extend from the first end to the second end of the sleeper, in the manner of a continuous profile. The cavity may be provided by a moulded structure.

However, the cavity may not have to be predefined for the core material. Instead, a core body may be provided in a different manner, for instance a material to form the core body may be co-deposited with surrounding first material that is intended to form the support structure.

In some embodiments, the support structure is a unitary body. The support structure may comprise a longitudinally extending upper plate, a longitudinally extending lower plate and two or more upwardly extending webs connecting the upper and lower plates.

The upwardly extending webs may define a cavity therebetween. The longitudinal cross-section of the support structure may therefore be generally box-shaped, i.e. square or rectangular, with the plates and webs forming the "walls" of the box. It will be understood that the terms "upper" and "lower" as used herein refer to the intended orientation of the sleeper in use, with the "lower" surface of the sleeper being adjacent to the ground, in use.

In alternative embodiments, the support structure is formed of two or more separate longitudinally extending members. For example, the support structure may comprise two U-shaped longitudinally extending members which face each other to define a cavity therebetween, wherein the cavity can be considered to be confined or 'closed' when viewed in the elongate extent of the sleeper. The longitudinally extending members may be configured to overlap such that the sides of one member are contained between the sides of the other member. Alternatively, one U-shaped member is wider than the other so that one U-shaped member can be nested within the other. The U-shaped members may be formed by a suitable technique such as by extrusion or moulding.

In some embodiments, the core body is located centrally within the sleeper, as viewed along the longitudinal axis. In some embodiments, the height of the core body is at least half of the height of the sleeper, where the height is measured in a direction between the lower and upper surfaces of the sleeper. In some embodiments, the height of the core body is at least two thirds, and preferably at least three quarters of the height of the sleeper. In embodiments comprising a cavity to receive core body material, the height of the core body may be defined by the dimensions of the cavity.

In some embodiments, the core material may extend from the first end to the second end. In embodiments comprising a cavity to receive core material, the core material may fill out the cross-section perpendicular to the longitudinal extension of the cavity.

In such embodiments, the core material may be provided only along certain parts of the cavity.

In embodiments, the core body may be located only in some regions along the sleeper, e.g. in the region of the first end and in the region of the second end. In some embodiments, the region between the core material at the first end and the core material at the second end may be provided with a filler material. The filler material may be a low density material, which reduces the weight of the sleeper compared to an elastic core material extending along the entire cavity. In some embodiments, the filler material may be a foam, such as a low density polyurethane foam. The region of the first and the second end can be designed to correspond with the regions of a sleeper that are beneath the rail tracks carried by the sleeper, such that the core body is located where screws are expected to engage with the sleeper.

In some embodiments a low density, rigid polyurethane foam may be used as a filler material. The density of the polyurethane foam may be no more than 60, 55, 50, 45, 40, 35, 30, 25, 20 or 15kg/m3.

As such, the core material may be inhomogeneous along the longitudinal extension of the sleeper. This allows a material composition to be selected for its suitability for engaging a fastener, e.g., its grip properties (grip properties for fastening-means) near the end of the sleeper, where fastening means are intended to be inserted to fix rail tracks to the sleeper, and another material composition to be selected for other properties, for instance for a reduced density or reduced material cost where fastenings are not required.

In some embodiments, the sleeper further comprises an outer structure at least partially surrounding or encasing the support structure. The outer structure may comprise recycled material, such as recycled polyvinyl chloride. In some embodiments, the outer structure may comprise a composite plastic material, which may include fibres, filaments, wires or the like. The composite plastic material may be made from mixtures of materials, such as plastic, rubber from used tyres, waste fibreglass and the like. In some embodiments, the outer structure may comprise a material such as high density polyethylene (HDPE). However, an outer structure is optional because the screw-engaging properties provided by the core body suffice for a secure engagement of the screws in the sleeper body.

In some embodiments, the outer structure may comprise an inner part of a first plastics material and an outer part of a second, different plastics material. The inner part may comprise recycled material, such as recycled polyvinyl chloride. The inner part may comprise a composite plastic material, which may include fibres, filaments, wires or the like. The composite plastic material may be made from mixtures of materials, such as plastic, rubber from used tyres, waste fibreglass and the like. The outer part may comprise a suitably hard-wearing plastics material, such as HDPE, which covers the inner part.

The outer structure may be formed around the support structure by any suitable method, for example by one or more moulding steps.

In some embodiments, extending portions of the upper plate and lower plate of the support structure extend laterally outwards beyond one or more of the upwardly extending webs, such that an outward-facing recess in the support structure is defined between the one or more upwardly extending webs and the extending portions, adjacent to the cavity. The extending portions may extend laterally outwards on both sides, such that a recess is defined on both sides of the cavity.

In some embodiments, the recess in the side of the support structure may accommodate an open, outwardly facing channel in the outer structure. The channel can be used to accommodate cables, such as communications, signalling or power cables underneath the rails. This allows the cables to be safely located within the silhouette of the sleeper and avoid damage from ballast tamping machines. In some embodiments, the channel may be provided with a cover plate to provide further protection to the cable or cables located within the channel. The cover plate may be removable. The cover plate may be held in place by a snap fit mechanism, or optionally with fixing screws. Alternatively, there may be provided longitudinally extending upper and lower grooves, into which a cover plate can be slid from one end of the sleeper. The cover plate may comprise a plastics material such as HDPE, uPVC or other polymers.

By way of the outwardly extending web of the supporting structure, the channel is better protected between the supporting structure material.

According to a second aspect of the invention, there is provided a method for manufacturing a sleeper according to certain embodiments of the first aspect. The method comprises the steps of forming the support structure by pultrusion, forming the core material, and placing the core material inside the cavity. In some embodiments, the method further comprises an optional step of moulding the outer structure around the support structure. The step of moulding the outer structure may be performed after placing the core material inside the cavity, thereby sealing the core material within.

Alternatively, the step of moulding the outer structure may be performed before placing the core material inside the cavity, in which case an end of the sleeper is left open, to be sealed by an end cap after the core material is placed inside the cavity. The core material may be formed by any suitable means, such as moulding.

Manufacturing the core material separately from the rest of the sleeper enables the size and shape of the core material to be controlled independently of the shape of the cavity defined by the support structure.

According to a third aspect of the invention, there is provided an alternative method for manufacturing a sleeper according to certain embodiments of the first aspect. The method comprises the steps of forming the support structure by pultrusion or extrusion, pouring the core material into the cavity in a pourable form, and allowing the core material to at least partially solidify inside the cavity. In some embodiments, the method further comprises an optional step of moulding an outer structure around the support structure. The step of moulding the outer structure may be performed after solidifying the core material inside the cavity, thereby sealing the core material within. Alternatively, the step of moulding the outer structure may be performed before solidifying the core material inside the cavity, in which case an end of the sleeper is left open, to be sealed by an end cap after the core material has been solidified inside the cavity.

Moulding the core material inside the cavity can ensure that the core material completely fills the cavity, leaving no gaps between the core material and the support structure.

According to a fourth aspect of the invention, there is provided a method for manufacturing a sleeper according to other embodiments of the first aspect. The method comprises the steps of forming the support structure by pultrusion, forming two portions of core material connected by longitudinally extending filler material, and placing the core material and filler material inside the cavity. In some embodiments, the method further comprises an optional step of moulding the outer structure around the support structure. The step of moulding the outer structure may be performed after placing the core material and filler material inside the cavity, thereby sealing the core material within. Alternatively, the step of moulding the outer structure may be performed before placing the core material and filler material inside the cavity, in which case an end of the sleeper is left open, to be sealed by an end cap after the core material and filler material is placed inside the cavity. The core material and filler material may be formed by any suitable means, such as moulding.

According to a fifth aspect of the invention, there is provided an alternative method for manufacturing a sleeper according to other embodiments of the first aspect. The method comprises the steps of forming the support structure by pultrusion, pouring the core material into the cavity in a pourable form, allowing the core material to at least partially solidify inside the cavity, pouring the filler material into the cavity in a pourable form, allowing the filler material to at least partially solidify, pouring a second portion of core material into the cavity in a pourable form, and allowing the second portion of core material to at least partially solidify. In some embodiments, the method further comprises an optional step of moulding the outer structure around the support structure. The step of moulding the outer structure may be performed after solidifying the core material and filler material inside the cavity, thereby sealing the core material and filler material within. Alternatively, the step of moulding the outer structure may be performed before solidifying the core material and filler material inside the cavity, in which case an end of the sleeper is left open, to be sealed by an end cap after the core material and filler material has been solidified inside the cavity.

In accordance with a sixth aspect of the invention, there is provided a track installation comprising a plurality of sleepers according to the first aspect and a pair of rails. The sleepers extend transversely underneath and support the rails, with fastening means securing the rails to the sleepers.

It will be understood that features and embodiments described in relation to any one of the preceding aspects may be used in combination with any one of the other aspects. For instance, features described in relation to the first aspect may be incorporated or made when carrying out any one of the second to sixth aspect.

Description of the Figures

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a lateral cross-section view of a sleeper in accordance with an embodiment of the invention; Figure 2 is a lateral cross-section view of a sleeper in accordance with another embodiment of the invention; Figure 3 is a longitudinal cross-section view of a sleeper in accordance with an embodiment of the invention; Figure 4 shows the Figure 3 embodiment during an installation step; and Figure 5 shows the Figure 3 embodiment during another installation step.

Description

Figure 1 shows a railway sleeper 100 according to an embodiment of the present invention, which extends longitudinally from a first end 10 to a second end 12. The sleeper 100 is depicted with an optional outer structure 20, formed of a plastics material, and a support structure 30 which extends longitudinally between the first and second ends 10, 12. The outer structure 20 is optionally moulded around the support structure 30. In some embodiments, an outer structure 20 is attached to only a few sides or to one side of the support structure. The support structure 30 defines a cavity 40 therein, which also extends longitudinally between the first and second ends 10, 12, i.e. along the entire length of the support structure. The cavity 40 is filled with a core material 42 that provides a separate core body such that fastenings can be attached to the core material 42 without requiring direct contact between the support structure 30 and the gripping element of the fastener. The core material may be comprised of a material which has a higher elasticity than the support structure 30.

In use, rails 60 are affixed to the sleeper 100 by way of fastenings 62, in the region of the first end 10 and the second end 12. The fastenings 62 penetrate through the outer structure 20 and support structure 30, into the core material 42. The core material 42 grips the fastenings 62, preventing loosening of the fastenings and providing suitable resistance to fastening pullout forces. The grip may be provided by a more elastic material, or by providing a material with fewer or no elongate reinforcing fibres than are provided in the support structure. In particular, as illustrated in Figures 4 and 5, the rails may be fixed to the core material without direct contact to the support structure 30.

To this end, prior to the insertion of the fastenings, a first hole may be drilled through the top layer of the support structure 30, exposing the core material 42. Then, a second hole may be drilled through the core material 42. The second hole may in practice extend through the entire sleeper including the lower layer of the support structure. The diameter of the first hole may be larger than the diameter of the shaft of the fastening 62. The diameter of the second hole may be smaller than the diameter of the fastening 62. Thereby, the fastening 62 can be inserted, e.g. screwed into the second hole without its shaft contacting directly the top layer of the support structure. The fastening 62 is engaged in the core material 42. Pull-out forces to pull the fastening 62 out of the sleeper would transfer via the fastening to the core material 42, and from the core material 42 against the inside (inside of the upper surface) of the support structure 40. Thereby, it is possible to provide an arrangement in which pullout forces acting on the support structure are distributed over the contact surface between the core material and the support structure inside, which is a larger surface area than would otherwise be provided with a fastening 62 directly engaging in the support structure.

Figure 2 shows another embodiment of a sleeper 110. In Figure 2, elements of the sleeper 110 corresponding to the sleeper 100 of Figure 1 are provided with the same reference numeral. In Figure 2, the cavity 40 is only partially filled with core material 42, with portions of core material 42 disposed only in the region of the first and second ends 10,12 where the rails 60 are to be affixed. The remainder of the cavity 40 is filled with a lighter filler material 44, such as a polyurethane foam, which reduces the overall weight of the sleeper.

Figure 3 shows a longitudinal section through an area containing core material 42, e.g. perpendicular to the section of the sleeper 100 of the Figure 1 embodiment or perpendicular through a portion near and end (one of ends 10, 12) of the sleeper 110 of the Figure 2 embodiment. As shown in Figure 3, the support structure comprises a longitudinally extending upper plate 31 and a longitudinally extending lower plate 32 connected by upwardly extending webs 33, with the cavity 40 being defined therebetween. The cavity 40 (in Figure 3 corresponding to the location of the core material 42) is located centrally within the sleeper, and the height He of the core material is at least three quarters of the height Hs of the sleeper. In embodiments, the height of the core material is at least half of the sleeper height, or at least 70, 80, or 90 percent of the sleeper height. In embodiments, the height of the core material is at least half, at least three quarters, or at least 70, 80 or 90 percent of a height Ht of the support structure. The support structure 30 may be provided at least partially with an outer structure.

Extending portions 34 of the upper and lower plates 31, 32 extend laterally outwards beyond the upwardly extending webs 33, defining recesses 35 laterally in the support structure 30, adjacent to and on either side of the cavity 40. The recesses 35 accommodate outwardly facing channels 21 in the support structure, which may be used to house cables or the like. The channels 21 are covered by a removable cover plate 22, which is held in place by snap fastenings or other suitable fastening means.

The channels 21 extend into the sleeper material and are covered, above and beneath, by an extending portion 34, which provides protection for the channel.

By way of the relatively large extent of the core material height relative to the sleeper height, once a fastener such as a screw is inserted through the upper plate 31 of the support structure 30, the remainder of the fastener can be fully inserted into the sleeper, to be surrounded by core material 42 along its entire length, without the end of the fastener abutting the opposite (lower) plate 32 of the support structure. This is useful for railway sleepers because it can be assumed that only a limited range of fasteners is used, and so the length of the fastener can be expected to be consistent for a length of railway track.

Figures 4 and 5 show two steps of an exemplary installation procedure using a sleeper 120. Sleeper 120 corresponds to the sleeper 100 of Figure 3. In Figures 4 and 5, the same numerals are used as in the preceding figures for corresponding elements and the description thereof is not repeated for brevity. In Figure 4, a first hole 46 has been drilled through the upper plate 31 to expose the core material 42. A second hole 48 has been drilled through the full height of the sleeper, i.e. through the core material 42 and through the lower plate 32. For the purposes of inserting a fastening 62, the second hole 48 does not need to extend through the full height of the sleeper but during installation particular of a great number of sleepers it may be practical to drill a through hole, rather than to ensure a bore of a certain depth has been drilled. With reference to Figure 5, the first hole 46 is wider than the shaft of the fastening 62 (not shown in Figure 4) and the second hole 48 is narrower than the shaft of the fastening 62. It will be understood that the second hole 48 could be provided before the first hole 46, but in practice creating the first hole 46 first allows the second hole 48 to be drilled without causing splintering of the upper plate 31.

Turning to Figure 5, this shows the embodiment of Figure 4 after the fastening 62 has been inserted into the core material 42. The fastening 62 connects a structure of the rail 66 to the sleeper 120. The fastening 62 comprises a threaded shaft 64 that grips the core material 42 without however contacting the upper plate 31, due to the spacing provided by the first hole 46 between the fastening 62 and the upper plate 31. Pull-out forces acting on the fastening 62 are transferred via the core material 48 onto the contact area between the core material 42 and the inside of the upper plate 31. As such the risk is reduced, and practically avoided, that loads are applied on the fastening 62 can be transferred to an only small area of the support structure.

While the support structure and the core material are separate components, they may due to the nature of the manufacturing of the sleeper exhibit certain adhesion properties and therefore stick together. For instance, both the support structure and the core material may comprise a fibre reinforced polymer resin, wherein the support structure is distinguished by longer fibres than the core material, but the polymer resin may be similar and therefore exhibit adhesive properties.

It will be understood that the sleeper of the present invention may be provided for installation without pre-drilled holes such as the first hole 46 and the second hole 48 described above. In other words, the sleeper may be provided to the site of installation in a configuration corresponding to Figure 3. Depending on baseplate design and screw type, a different arrangement of holes may have to be drilled into the sleeper on site. It is an advantage of the present invention that the core material can be designed to have screw-gripping properties similar to that of the sleeper to be replaced. For instance, if the sleeper of the present invention is provide to replace hard wood sleepers, the core material may be designed to correspond to the grip properties of hard wood sleepers. This allows the same screws to be re-used when replacing a hard wood sleeper with a sleeper of the present invention. In that case, while the core material can be modified to provide specific grip properties, it is not necessary to redesign the support structure. This facilitates manufacture and increases the versatility of the present sleeper.

The core material may be designed to have grip properties comparable to hardwood, such that screws from wood sleepers to be replaced may be reused and so that the installation equipment is similar to that for hardwood sleepers. The cavity 40 can be designed to extend over a large proportion of the overall height of the support structure 30, such that when provided with core material 42, screws of a length typically used in rail tracks can bite into core material without the end of the screw abutting a more rigid material of the support structure.

The embodiments of Figures 1 to 5 describe a railway sleeper made from a pultruded support structure with a cavity defined by the extrusion profile. The support structure may be manufactured by a moulding process. As such, the core material may be provided within the support structure directly, e.g. without having to first provide a cavity.

Claims

CLAIMS: 1. A railway sleeper which extends longitudinally from a first end to a second end, the sleeper comprising: a support structure extending longitudinally between the first and second ends, the support structure comprising a first material; wherein the support structure comprises along at least part of its longitudinal extent between the first and second ends a core comprising a second material providing a core body that can be engaged by a fastener to be provided thereby reducing a direct transfer of pull-out forces from the fastener onto to support structure.
2. The sleeper according to claim 1, wherein the support structure defines a cavity therein, the cavity extending longitudinally between at least a portion of the first and second ends, wherein the second material is provided in the cavity.
3. The sleeper of claim 1 or 2, further comprising an outer structure at least partially encasing the support structure.
4. The sleeper of any one of the preceding claims, wherein the support structure comprises a composite material, optionally wherein the composite plastic material includes reinforcing fibres, filaments or wires.
5. The sleeper of any one of the preceding claims, wherein the support structure comprises a longitudinally extending upper plate, a longitudinally extending lower plate and two or more upwardly extending webs connecting the upper and lower plates.
6. The sleeper of claim 5, wherein extending portions of the upper plate and the lower plate extend laterally outwards beyond one or more of the upwardly extending webs, such that a recess in the support structure is defined between the one or more upwardly extending webs and the extending portions.
7. The sleeper of claim 6, comprising an outer structure, wherein the outer structure is provided with an outwardly facing channel corresponding to the recess in the support structure.
8. The sleeper of claim 7, wherein the outwardly facing channel is provided with a removable cover plate.
9. The sleeper according to any one of the preceding claims, wherein the core body is located centrally within the sleeper as viewed along a longitudinal axis.
10. The sleeper according to any one of the preceding claims, wherein the height of the core body is at least half, preferably at least two thirds, more preferably at least three quarters of the height of the support structure.
11. The sleeper of any one of the preceding claims, wherein the support structure comprises a synthetic material, optionally wherein the synthetic material is a vinyl ester, polyester, epoxy or polyurethane resin.
12. The sleeper of any one of the preceding claims, wherein the core body extends longitudinally from the first end to the second end.
13. The sleeper of any one of claims 1 to 11, wherein the core body is located in the region of the first end and in the region of the second end thereby to provide a fastener-gripping material beneath tracks to be provided.
14. The sleeper of claim 13, wherein a filler material is disposed between the core material at the first end and the core material at the second end.
15. The sleeper of claim 14, wherein the filler material is a foam, optionally wherein the foam is a low density polyurethane foam, optionally having a density of no more than 60, 55, 50, 45, 40, 35, 30, 25, or 15 kg/m3.
16. A method for manufacturing a sleeper according to claim 12, comprising the steps of: forming the support structure by pultrusion, the support structure defining a cavity therein; forming the core material, optionally by moulding; placing the core material inside the cavity; and optionally moulding an outer structure around the support structure, wherein the step of moulding the outer structure is performed either after placing the core material inside the cavity, thereby sealing the core material within the support structure, or before placing the core material inside the cavity, leaving an open end of the sleeper to be sealed by an end cap after the core material is placed inside the cavity.
17. A method for manufacturing a sleeper according to claim 12, comprising the steps of: forming the support structure by pultrusion, the support structure defining a cavity therein; pouring the core material into the cavity in a pourable form; allowing the core material to at least partially solidify inside the cavity; and optionally moulding an outer structure around the support structure, wherein the step of moulding the outer structure is performed either after solidifying the core material inside the cavity, thereby sealing the core material within the support structure, or before pouring the core material into the cavity, leaving an open end of the sleeper to be sealed by an end cap after the core material has been solidified inside the cavity.
18. A method for manufacturing a sleeper according to claim 14 or claim 15, comprising the steps of: forming the support structure by pultrusion, the support structure defining a cavity therein; forming two portions of core material connected by longitudinally extending filler material, optionally by moulding; placing the core material and filler material inside the cavity; and optionally moulding an outer structure around the support structure, wherein the step of moulding the outer structure is performed either after placing the core material and filler material inside the cavity, thereby sealing the core material and filler material within the support structure, or before placing the core material and filler material inside the cavity, leaving an open end of the sleeper to be sealed by an end cap after the core material and filler material have been placed inside the cavity.
19. A method for manufacturing a sleeper according to claim 14 or claim 15, comprising the steps of: forming the support structure by pultrusion, the support structure defining a cavity therein; pouring a first portion of core material into the cavity in pourable form; allowing the first portion of core material to at least partially solidify; pouring the filler material into the cavity in pourable form; allowing the filler material to at least partially solidify; pouring a second portion of core material into the cavity in pourable form; allowing the second portion of core material to at least partially solidify; and optionally moulding an outer structure around the support structure, wherein the step of moulding the outer structure is performed either after allowing the core material and filler material to at least partially solidify inside the cavity, thereby sealing the core material and filler material within the support structure, or before pouring the core material and filler material into the cavity, leaving an open end of the sleeper to be sealed by an end cap after the core material and filler material have been allowed to at least partially solidify inside the cavity.
20. A track installation comprising a plurality of sleepers according to any one claims 1 to 15 and a pair of rails, the sleepers extending transversely underneath and supporting the rails, with fastening means securing the rails to the sleepers.