Tie

Abstract

Present invention concerns a tie being the carrying element for rails in a railway track. The tie comprises means (1) for fastening the rails to the tie which in use is lying in a ballast bed of crushed stone at the formation plane of the line. At the underside (2) the tie is provided with a number of elevations (4), whose height (H) is 40-100% of Dmax of the crushed stone. Each elevation (4) protrudes across the tie, and constitutes a cogging towards the crushed stone, in the longitudinal direction of the tie.

Description

[0001] The invention relates to a tie as the carrying element for rails in a railway track, according to the preamble of patent claim 1.

BACKGROUND

[0002] A conventional railway track is composed of two longitudinal steel rails attached by rail attachments to crosswise ties of wood, concrete or steel. The ties are supported by a ballast of crushed stone resting on the formation level of the line. It is an advantage to use all-welded railway tracks with continuous tracks, when considering speed, safety, comfort, maintenance needs and costs.

[0003] When a train passes along the rails, the rails are loaded from the rolling stock. These loads are mainly vertical to the rails. However, due to train load, acceleration and braking, driving in curves and temperature variations, there are in addition, considerable horizontal forces affecting the rails both transverse and longitudinal to the rails.

[0004] The longitudinal forces are extra large in curves due to the curvature. Upon a large increase in temperature, the sum of the axial pressure on the rails, among other factors due to expansion of the material in the rails upon an increase of the temperature, may get so large that the railway track snaps out to the side, both in straight lines and in curves. This is called sun loops. Previously large axial pressures in the rails arising from temperature rises, were avoided by using relatively short rails placed with a short distance between, so-called heating spaces, in order to allow for temperature expansion. The rails were joined together with fishes and fish bolts. These fish joins are expansive, they need a lot of maintenance, reduce the comfort and involve high wear on other bed components and rolling material.

[0005] Both vertical and horizontal forces in the rails are transferred through the rail attachments to the ties. The ties are held in place by friction and inactive earth pressure in the ballast layer. In order to ensure that the track has good side-stability, there is a demand for sufficiently large resistance to any sideways displacements of the ties.

[0006] Underneath a railway carriage, the rails distribute the wheel-loads to the nearest ties and the rails undergoes a deflection due to the load. Thus, the railway track also experience small flection upwardly, a “lifting wave” in front of and behind the wheel axles. In that the part of the rail experiencing the lifting wave, there will be reduced contact between the underside of a standard concrete tie and the ballast layer, and resistance to lateral displacement will be correspondingly reduced. It is observed that sun loops often are formed by the railway track being cracked out underneath, or behind a carriage when the train passes over parts of the track having large temperature pressures in the rails.

[0007] In order to avoid the problems with fished tracks, and to improve the quality of the track and safety, all-welded tracks with continuous rails are being used upon new building and modernization. An all-welded track is a stronger track construction demanding rails with improved resistance to bending, elastic rail connections having greater resistance to twisting, and heavier ties placed less distance apart. This provides a railway track which in practice is strong enough to absorb the sum of the axial pressures in the rails, included those due to temperature variations, without danger for cracking out a track in straight line or in gentle curves.

[0008] In curves having a radius smaller than 250-300 m, the forces for displacement to the side upon maximum temperature- and traffic-stress are so large, that tracks with all-welded rails might crack out and result in derailment. A fished track must still be used for sharp curves.

[0009] Important factors crucial to resistance against cracking out of the railway track, are amongst others the rails' resistance towards bending, the rail connections' resistance to twisting, the distance between the ties, and ties' the resistance to displacement to the side. However, the ties' resistance towards displacement to the side has a particularly strong influence.

[0010] One solution which has been used to increase the resistance towards displacement to the side, is to fasten the tie in the bed by means of different tie anchors, for instance as described in DE OS 3839 998. However, this is a work intensive and expensive method, and in addition, tie anchors form a certain impediment upon adjustment of the track geometry and other maintenance work on the track.

[0011] The side stability may also be improved by expanding the formation plane through narrow curves, and thus increase the end resistance of the ties with a broader ballast shoulder. However, in most cases this demands a difficult and expensive construction work.

[0012] A regular type of tie for all-welded tracks, is a pot sleeper tie of prestressed concrete. It has mainly the shape of a balk with a little narrower central part and trapeze-shaped cross-section, wherein the lateral surfaces slant slightly downwards and outwards. When disregarding the effect of a narrower central part, the resistance towards axial displacement of such a standard concrete tie in crushed stone, for an unloaded railway track, may mainly be split into three parts; earth pressure on the end faces and friction towards the vertical lateral faces and the underside. The two former parts normally constitutes just a minor part of the tie's resistance to side displacement, while the last part is far more important for both unloaded and loaded tracks. The side displacement forces are transferred from the tie to the ballast and create shear stress in the contact tips. As long as the shear stress is less than the friction- and hooking-resistance in the contact tips, the tie does move, but when this resistance is exceeded, the tie is displaced by slippage towards large crushed stones in the interface, and by some turning and rotation of smaller crushed stones towards the concrete face. What is distinctive of this displacement process is that the resistance towards displacement is mainly determined by the friction upon slipping of crushed stones towards a plain concrete face, and the resistance towards turning and rotation of crushed stone in the interface towards this face.

[0013] In patent application EP 919,666 there is described a steel sleeve placed on the outside of a concrete tie. The steel sleeve is provided with vertical ribs on the vertical lateral faces, in order to improve the adhesion in the ballast bed. In U.S. Pat. No. 5,104,039 there is mentioned an embodiment having vertically, cotter-formed, shallow recesses in the vertical lateral faces, in order to increase the friction and the hooking. The effect of both of these embodiments will strongly depend on the moderate horizontal pressure in the ballast material between the ties, and is limited by this.

[0014] In patent application DE 2,735,797 there is described a concrete tie having large chamber shaped recesses in the vertical lateral faces of the tie, and preferably a profile on the underside in the form of a number of rhomb-formed elevations. In the figures there is shown a close pattern of rhomb-formed elevations on the underside. With this embodiment a certain hooking-effect will be achieved in addition to friction, but upon displacement the crushed stone in the ballast will mainly slip upon and roll around the small rhomb-shaped faces of concrete on the underside of the tie.

[0015] Patent application DE 411,1088 relates to a concrete tie wherein the tie is provided with a slim central part and broad end parts. The vertical lateral faces at the end parts are provided with a number of vertical recesses. As with the ties according to EP 919,666 and U.S. Pat. No. 5,104,039 the effect of the hooking of the ballast in these recesses will be a function of the horizontal pressure in the ballast bed towards the vertical lateral faces of the tie, and be limited by this. It is further mentioned that the underside of the tie may be provided with crosswise recesses, in the outer third of the length. In the description it is said that it is not necessary to increase the cross-section of the tie, and thus the recesses must be so shallow that the friction effect of them will in practice, be very limited.

[0016] U.S. Pat. No. 1,032,045 discloses a tie where the central part of the underside is provided with a broad longitudinal ridge-formed recess. In the lateral faces of this recess, there are made small shallow slantwise grooves, creationg a fishbone-looking pattern. The recesses and grooves will also, for this tie, be so shallow that the friction-effect being achieved will be very limited.

[0017] None of the previously known solutions seem to have satisfied the need for a tie having sufficiently large resistance to side-displacement, for use in all-welded tracks in curves with small radius' and in climates having large temperature variations.

OBJECT

[0018] The main object of the present invention is to provide a tie with considerably increased resistance to side displacement, compared to known ties, so that in use there is achieved a railway track with increased stability. A further object of the invention is that the tie should be relatively easy to produce and easy to place and use.

THE INVENTION

[0019] The object is fulfilled with a tie according to the characterizing part of patent claim 1. Further advantageous features are given in the dependent claims.

[0020] A tie according to the present invention provides better fastening in the ballast bed, and moves the shear zone upon sidewards movement, down into the crushed stones, so that the inner stone against stone friction is utilized and provides increased resistance to side displacement, and thus increased effective friction towards side displacement. The inner friction in crushed stone is much larger than the friction between crushed stone and a flat concrete face when the stone slips, turns or rotates against this.

[0021] By using a tie according to the present invention, the side stability of a railway track could be improved enough to use all-welded tracks through curves having less radius' than what is put into practise with known solutions. Use of ties according to the present invention in gentle curves and on straight lines will also contribute to better track stability, which will result in less need for track maintenance and less expensive and more effective operation. Use of ties according to the present invention may also improve the general track stability for high velocity tracks.

[0022] A tie according to the present invention is provided with a number of elevations on the underside, meaning that side turned toward the ballast bed when the tie is in use. The structure of the elevations is adjusted to the size of the ballast material in such a way that a layer of crushed stone will lock into the underside of the tie upon packing and vibrations due to traffic. Upon displacement of the tie, the shear zone has to go through the underlying crushed stones in the ballast bed.

[0023] The material in the ballast bed is generally so tightly packed that the crushed stones become well interengaged in a stable framework. Displacement of a tie according to the present invention, thus requires that the framework in the shear zone must be expanded so that the hooking mechanisms are destroyed.

[0024] In order to achieve this effect, the elevations on the underside of the tie must be embodied strictly in accordance with the dominating size of the crushed stones in the ballast layer. The height of each elevation must ensure good hooking and prevent the slipping or tipping over of the crushed stone. The distance between the elevations at the underside of the tie, must be appropriately large to achieve good wedging of large crushed stones that may be locked with less crushed stones in the framework formed lengthwise and widthwise. The vertical or slanting sides of the elevations must be steep enough to provide good hooking of crushed stones towards the edges, at the same time as they must give the space between the form of a wedge, give an appropriate locking effect when the ballast material is pressed into the space between the elevations. It is an advantage if the elevations have the shape of a trapeze. Finally, the width of a downward horizontal face of each elevation in the longitudinal direction of the tie, must be adjusted so that the elevation both receives enough strength to withstand current stress, and that downward vibration into the ballast bed is minimised. At the same time, the width of the horizontal face should also be kept relatively narrow, so that crushed stones of appropriate size become sufficient attachment between the wedged crushed stones sticking out on both sides of the elevation, and in that way get secured in a mainly continuously fastened layer of crushed stone on the underside of the tie.

[0025] The distance between two elevations should preferably be the same along the tie, and the width of the downward face of the elevations in the longitudinal direction of the tie, should also be the same along the tie, so that an even cogging is achieved. In this case, the distance between two elevations, at the underside of the tie, will always be the same or preferably larger than the width of the downward face of an elevation in the longitudinal direction of the tie. Without regard to whether the distance between two elevations is equal or not, the sum of the distances between two elevations, at the underside of the tie, should always be the same or preferably larger than the sum of the width, in the longitudinal direction of the tie, of the downward face of each elevation with the exception of one, so that the number of elevations and the number of distances between elevations which are used in the calculations, are the same. Mathematically this relation may be expressed as the following: 1$\sum _{i=1}^n{F}_i\ge \sum _{i=1}^n{B}_i$

[0026] wherein F is the distance between two elevations at the underside of the tie, B is the width of the downward face of an elevation in the longitudinal direction of the tie, and n+1 is the number of elevations on the tie.

EXAMPLE

[0027] The present invention will in the following be described with reference to drawings, wherein

[0028] FIG. 1 is a view from above of a tie according to the present invention,

[0029] FIG. 2 is a longitudinal section of a tie, along line I-I in FIG. 1,

[0030] FIG. 3 is a cross section of a tie, along line II-II in FIG. 1 and 2, and

[0031] FIG. 4 is an enlarged section of the underside of a tie according to the present invention.

[0032] As shown in FIG. 1, a tie according to the present invention is mainly embodied as a traditional pot sleeper tie, with the exception of the underside. The upper side is provided with means 1 for fastening rails to the tie. The central part of the tie is a bit narrower than the end parts. The cross section of the tie (FIG. 3) has the form of a trapeze, wherein the face 2 turning down towards the foundation, is larger than the face 3 turning up towards the rails. With the exception of the underside, the tie may have any shape, as this is not part of the invention.

[0033] The underside of a tie according to the present invention, is provided with a number of elevations 4, see FIG. 2. These should have a height H corresponding to about 40-100%, preferably 50-70%, more advantageously 60% of Dmax of the crushed stones constituting the ballast bed in which the tie rests. The underside of a tie according to the present invention is shown in detail in FIG. 4. If the foundation is not crushed stone, but another material in preferably large units, the height H should correspond to 40-100%, preferably 50-70%, more advantageously 60% of Dmax of these units.

[0034] In this connection, Dmax is meant to be the largest nominal grain size of the crushed stone. Dmax for crushed stone to be used for ballast beds for ties, according to Norwegian specifications, is 6,3 cm.

[0035] The stones are moved in between the elevations by packing, pressure and vibrations, either upon track adjustment, or by the passage of rolling material thereover. Upon displacement of a built-in tie, a layer of crushed stone will be fixedly held between the elevations at the underside of the tie by wedging, hooking and friction, that the shear zone in the displacement band will be forced to go through the ballast material. The relatively high internal friction in the crushed stone in the ballast is thus utilized, and the tie thereby receives high resistance to side-displacement.

[0036] As the rolling material passes over, the tie is pressed into the ballast bed, and fixedly held extra well by means of the elevations 4 at the underside. This is important, because it is during the passage of rolling material that the largest side displacement forces and dynamic effects occur.

[0037] Each elevation 4 protrudes across the tie. The elevations 4 may protrude for just part of the width of the tie, but it is advantageous if they protrude over the whole of the width, so that transverse grooves 5 are formed between the elevations 4 along the whole of the width. If the elevations only protrude across part of the width, the layer of crushed stones being held steady at the underside of the tie, will be correspondingly reduced. A minor part of the shear face will thus utilize the inner friction of the ballast layer, and the total side displacement resistance will be less.

[0038] In order to achieve the best result, it is further an advantage that the elevations 4 are placed over the whole underside 2 of the tie, so that they constitute a continously cogging. The distance D from center to center of two elevations, should preferably be about 2 times Dmax of the stones in the foundation.

[0039] Preferably, the cross-section of the elevations have the form of a trapeze, shown in FIG. 4, wherein the downward horizontal face 6 of an elevation 4, is less than the face of the elevation bearing against the underside of the tie. The angle Φ between the vertical lateral faces 7 and the plane through the horizontal face 6 facing towards the foundation, is about 65-75 degrees, preferably 70 degrees. This or corresponding shapes of the elevations 4 will ensure that the crushed stones slips easier into the groove 5 between two elevations 4, as the tie is pressed down and locked steady by hooking and wedging into the ballast bed.

[0040] With a tetragonal cross section of the elevations 4, the elevations will be weaker, the edges will more easily be broken off, and the effect of the elevations will thus be reduced. With a trapezoidal cross section, the elevations will be stronger, the edges will not so easily break off, and stones will more easily slip to the side and into the groove 5 between the elevations 4 when these are being pressed down into the ballast layer.

[0041] With a triangular cross section of the elevations, stones will slip into the grooves 5 between the elevations 4, and it will require lower forces to press the tie down into the foundation. However, the tip of the triangle will easily break off, and the effect of the elevation will be reduced. The tip of a triangular elevation will also easily break upon production, transportation and placement.

[0042] With a trapezoidal cross section of the elevations, the width B of an elevation 4, meaning the width of the horizontal face 6 facing towards the foundation, measured in the longitudinal direction of the tie, should be 45-60%, preferably 50% of Dmax of the crushed stone. The angle Φ between the vertical lateral faces 7 and the plane through the horizontal downward face 6, should be about 65-75 degrees, preferably 70 degrees, in order to achieve sufficient efficiency and strength of the elevation 4.

[0043] If the Dmax of crushed stone is 6,3 cm, a possible embodiment of a tie according to the present invention will have on the underside 2, elevations 4 being about 3,8 cm tall (H=3,8), where the distance between two elevations 4, from center to center will be about 12,6 cm (D=12,6), and the width of the horizontal face 6 of the elevation 4 facing towards the foundation, will be about 3,2 cm (B=3,2). The rest of the tie will preferably be embodied according to standard tie JBV 97.

[0044] As will be understood by persons skilled of the art, the present invention is not only limited to what is mainly shown and described above. The invention also comprises combinations and subcombinations of the above described features, modifications and variations of these being obvious to a person familiar with the known technique, and within the scope of the following claims.

Claims

1. Tie as the carrying element for rails in a railway track, comprising means (1) for fastening the rails to the tie, the tie in use lying in a ballast bed of crushed stone on the formation plane of the railway track, wherein the tie has a number of elevations on the underside, each elevation protruding across substantial parts of the width of the tie, characterized in that the height (H) of each elevation is 40-100% of Dmax of the crushed stone, and that

2. Tie according to claim 1, characterized in that the distance (D) between the center of two elevations (4) corresponds to about 2 times Dmax of the stones in the ballast bed.

3. Tie according to claim 1, characterized in that the height of each elevation is 50-70%, preferably 60% of Dmax of the crushed stones.

4. Tie according to claim 1, characterized in that each elevation (4) protrudes across the whole width of the tie, so that transverse grooves (5) between the elevations (4) are formed.

5. Tie according to anyone of the preceding claims, characterized in that the elevations (4) have a trapezoidal cross section, wherein the width (B) of the downward face (6) in the longitudinal direction of the tie, corresponds to about 45-60%, preferably 50% of Dmax of the stones in the ballast bed.

6. Tie according to claim 5, characterized in that the elevations (4) are symmetrical, and that a angle (Φ) between the vertical faces (7) and the plane through the downward face (6) of the elevation (4), is about 65-75 degrees, preferably 70 degrees.

7. Tie according to any one of the preceeding claims, characterized in that the tie is provided with elevations (4) and grooves (5) over the whole length thereof, so that a cogging is achieved.