Abstract:
A superstructure arrangement for a track comprising a rail fastened to a securing device such as a ribbed plate which is disposed above a concrete sleeper, with an intermediate layer extending between the sleeper and the securing device. The rigidity of the intermediate layer is variable and rated so that at the maximum permissible stress in the rail, caused by bending under wheel lead, the elastic property changes to substantially non-elastic.

Description:
The present application is a continuation of application Ser. No. 09/051,476 filed Aug. 11, 1998, now U.S. Pat. No. 6,027,034, which is a 371 PCT/EP96/04536 filed Oct. 18, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a superstructure construction comprising a rail disposed above a support layer such as a concrete sleeper and in its turn extending from a securing device such as a ribbed plate, where at least one intermediate layer with a rigidity x is disposed between the support layer and the securing device. 
     Bedding sleepers on ballast or resorting to designs with a ballastless track and stable, rigid sleeper mountings are known. In the latter case, the sleeper such as a concrete sleeper is placed on asphalt or concrete supporting plates or suitable troughs and then partially cast in place using a sealing compound such as concrete or asphalt. 
     To achieve a reduction of the structure-borne and airborne sound emitted by a rail in ballastless tracks, a construction is known where a standard rail such as S 54  is placed on a cork layer inside a channel comprising concrete or steel parts. In addition, cavities are provided that are filled at the top with a polyurethane/cork mixture to reduce sound. 
     However, this construction has not brought the desired result, and indeed sound measurements show that there has even been a 10 dB sound increase compared with the ballast construction. 
     A device for mounting rails for rolling stock is known from DE 89 15 837 U1, in which a ribbed plate is disposed on an elastic intermediate layer whose thickness is at least that of the ribbed plate. The intermediate layer can here have a required elasticity thanks to certain geometrical parameters. The same applies for DE 40 11 013 A1, which relates to a tempered rail structure for high-speed tracks. It is intended here to ensure, by providing a cavity with plastic-modified adhesive mortar, that a direct transmission of heat energy or cooling energy to the rail is prevented. 
     According to DE 41 38 575 A1, the spring rigidity of an elastic intermediate layer can be designed dependent on the contact force. 
       
     EP 0 632 164 A1 contains the proposal to structure the bottom of an elastic intermediate layer such that under load a higher rigidity results, while the transmission of sound is to be restricted at the same time. 
     An elastic rail support layer with bottom compression points and all-round closed edge strip is known from DE 43 14 578 A1. 
     The problem underlying the present invention is to develop a superstructure construction, in particular one on a ballastless track, such that a reduction of structure-borne and airborne sound is achieved. 
     The problem is substantially solved in accordance with the invention in that the rigidity x of the intermediate layer is rated such that at the maximum permissible and/or presettable rail stress in the rail the intermediate layer has substantially non-elastic properties such that further bending of the rail only takes place insubstantially if at all. 
     In accordance with the invention, the intermediate layer is rated for the permissible or required maximum rail stress, which has the advantage that the rail itself is on a softer support, thus achieving a decoupling between the rail and the sleeper. The effect of this is a lower loading of the support point and in turn a reduction in the structure-borne sound. This can be improved by using as rails those with high moment of inertia and moment of resistance when seen over the rail central axis, for example a filled section rail, so that the rail can perform the function of a support and develop a load-bearing effect. This results in a further decoupling between rail and sleeper, whereby a further reduction is achieved of the structure-borne sound emitted by the rail when it is traversed by rolling stock. 
     An intermediate layer is proposed that has a low rigidity before the maximum permissible and/or presettable rail stress is reached and a high rigidity when this rail stress is reached. 
     It is preferably provided here that the intermediate layer has a rigidity x of x≦25 kN/mm, preferably 4≦×≦25 kN/mm, and/or that at the maximum permissible rail stress the intermediate layer has a rigidity x of x≧35 kN/mm, in particular x≧90 kN/mm, preferably in the vicinity of 100 kN/mm. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, it is proposed that when the intermediate layer is without load it has projections extending beyond its underside and is surrounded within the intermediate layer by a cavity (recess) on the circumferential side. The cavity has a volume V a , which is equal to a volume V b  that the respective projection has in its section projecting beyond the underside. 
     Thanks to the structure in accordance with the invention, the projections have the function of a supporting spring which is effective when the maximum rail stress of the rail supported by the support layer has not yet been reached. If this is then reached, the projections are forced into the support layer such that the projections are flush with the underside of the intermediate layer and at the same time fill the entire cavities (recesses). As a result, the form factor of the intermediate layer is increased such that the maximum permissible rail stress is not generally exceeded even when further forces are introduced. The intermediate layer should have a rigidity x which is in the vicinity of 100 kN/mm in particular when the cavities in the support layer are completely filled by the material of the projections. 
     It is provided in particular that the rail is a Vignol rail with a maximum permissible rail stress of 70 to 100 N/mm 2  and that the intermediate layer has a rigidity x of approximately 4 to 16 kN/mm, provided the maximum permissible rail stress has not yet been reached. 
     Apart from the geometry of the rail, an embodiment of the invention provides that in particular rails are used that have a moment of inertia I x  with preferably I x ≧3400 cm 4  and a moment of resistance W x  with preferably W x ≧350 cm 3 . 
     In particular, a superstructure construction with ballastless track is provided in which the rail is a filled section rail with a moment of inertia I x  of 3700≦I x ≦3800 cm 4  and a moment of resistance W x  of 390≦W x ≦410 cm 3  and a maximum required rail stress σ can be generated (approx. 70±4 N/mm 2  for rail steel UIC Class A with 880 N/mm 2  tensile strength) and the intermediate layer has a rigidity x of approximately 10±2 kN/mm for filled section tracks. In the case of traffic carriers with low axle loads, rigidities lower than the previously stated value are obtained. 
     In an embodiment of the invention, the arrangement provides for the rail to be designed at its foot such that the latter emits sound waves with a frequency v when vibrations are excited, said waves being substantially outside a frequency range between 500 and 3000 Hz. This results in a rail foot design in respect of its vibration technology that ensures a considerable reduction of the airborne sound. 
     In addition, the rail can be designed without a web, which also prevents problems from unwelcome airborne sound. 
     If the rail has a web, the latter should be designed such that it emits sound waves with a frequency v when vibrations are excited, said waves being substantially outside a frequency range between approximately 500 and 3000 Hz. 
     To ensure that the rail cannot tilt due to the fact that it rests on a relatively soft intermediate layer with its securing device, an embodiment of the invention provides that the rail forms together with the securing device such as a ribbed plate a unit which has the effect of widening the rail. The securing device here can be positioned inside the intermediate layer and enclosed by the latter along its longitudinal edge. 
     Further details, advantages and features of the invention are shown not only in the claims and in the features they contain—singly and/or in combination—but also in the following description of preferred design examples shown in the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a section through a superstructure construction with a first embodiment of a Vignol rail, 
     FIG. 2 a section through a superstructure construction with a second embodiment of a Vignol rail, 
     FIG. 3 a section through a superstructure construction with a filled section rail, 
     FIG. 4 a section through an intermediate layer with low effective rigidity, 
     FIG. 5 the intermediate layer according to FIG. 4 with high effective rigidity, and, 
     FIG. 6 a characteristic. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The figures—where as a general rule identical elements are identified by identical reference numbers—show sections through a ballastless track comprising a concrete sleeper  10 , a ribbed plate  16  connected thereto by bolts  12 ,  14 , and a rail attached to this ribbed plate, the rails being a UIC 60  rail  18  in FIG. 1, a Vignol rail  20  in FIG. 2, which has a changed vibration technology compared with the UIC 60  rail  18  in respect of the web  22  and the foot  24 , and a filled section rail  26  in FIG.  3 . 
     The respective rails  18 ,  20 ,  26  are secured to the ribbed plate  16  using suitable fasteners such as clips  28 ,  30  resting on the feet  24  or  32 ,  34  of the rails  20  or  18  and  26  respectively. Here the connection between the fasteners  28  and  30  and the respective rail feet  24 ,  32 ,  34  is such that a mechanical unit is formed that leads to an apparent widening of the rail foot. As a result, the respective rail  18 ,  20 ,  26  attains a greater tilting stability. 
     As regards the fastening of the ribbed plate  16  to the concrete sleeper  10  using the bolts  12  and  14 , reference is made to standard designs, in particular however to those found in WO 95/17552. 
     Regardless of the type of fastening between the ribbed plate  16  or element with the same effect and the sleeper  10 , however, it is provided in accordance with the invention that an elastic intermediate layer  36 ,  38 ,  40  passes between the ribbed plate  16  or corresponding securing device for the rail  18 ,  20 ,  26  respectively and the sleeper  10 , said intermediate layer having a rigidity x that depends on the maximum required rail stress of the respective rail  18 ,  20 ,  26 . In this case the ribbed plate  16  is preferably vulcanized into the intermediate layer  36 ,  38 ,  40 , which in turn has a so-called kinked rigidity characteristic. This means that the intermediate layer  36 ,  38 ,  40  has properties which are soft in that working range in which the rail  18 ,  20 ,  26  has not yet reached the maximum permissible rail stress, but then abruptly become hard when the maximum permissible rail stress prevails. To obtain a so-called kinked characteristic, design measures to be found in WO 94/08093 can be selected. 
     In particular however, the measures to be found in FIGS. 4 and 5 must be provided, in order to set the rigidity of the intermediate layer such that its properties are soft before the maximum permissible rail stress is reached, and then change abruptly to hard properties when the maximum permissible rail stress prevails. 
     An intermediate layer  36 ,  38 ,  40  shown in FIGS. 1 to  3  can in its principle have a design as shown in FIGS. 4 and 5 and provided with the reference number  42 . The intermediate layer  42  therefore has projections  46  projecting beyond its underside  44 . At the same time, the projections  46  are surrounded by a cavity  48  (recess in the intermediate layer  42 ) when the intermediate layer  42  is without load. This cavity  48  has a volume V u  corresponding to the volume V b  of that section  50  of the projections  46  which extends beyond the underside  44  of the intermediate layer  42 . 
     The projections  46  perform, under standard loading of the rail, i.e. before the maximum permissible rail stress is attained, supporting spring functions, and accordingly support the ribbed plate  16  alone. As the force introduced increases and, concomitantly, the rail stress likewise increases, the projection  46  is forced more and more into the intermediate layer  42 , the result being that the cavity  48  is filled by the material of the projection  46 . When the maximum permissible rail stress is reached, the projection  46  fills the entire cavity  48 , so that as a consequence thereof the front face  52  of the projection  46  is flush with the underside  44  of the intermediate layer  42 . Because of this, the entire intermediate layer  42  performs supporting functions, with the result that the intermediate layer as a whole is effective with a high rigidity. This in turn means that when further forces are introduced into the rail its rail stress can only be increased insubstantially, if at all. 
     FIG. 5 shows the intermediate layer  42  with the projections  46  forced into it. It can be seen that the front faces  52  of the projections are aligned with the underside  44  of the intermediate layer  42 . 
     FIG. 6 shows purely in principle the characteristic of the intermediate layer  42 . The subsidence s is therefore shown as a function of the force acting on the intermediate layer  42 . In the area in which the maximum permissible rail stress has not yet been reached the characteristic has a flat curve, which rises steeply when the maximum permissible rail stress has been reached. 
     In other words, the intermediate layer  42  is designed such that the rail is bendable enough that the maximum permissible rail stress can be generated and when the latter is reached no further bending is possible, since the intermediate layer  42  has a high rigidity x which is preferably in the vicinity of 100 kN/mm or more. 
     The maximum permissible rail stress is that rail stress which can occur at the foot underside and can be ascertained using a measuring strip, for example. It is provided here for ballastless tracks that the maximum required rail stress is 70±4 N/mm 2  with a standard wheel load of 10 t in rolling stock traversing the rail. 
     To permit an appropriate maximum rail stress when rolling stock with a wheel load of 10 t traverses the rail, the rigidity x of the respective intermediate layer  36 ,  38 ,  40  is rated accordingly, i.e. the rigidity x of the intermediate layer  36 ,  38 ,  40  compared with known superstructure constructions is reduced, meaning that the rail  18 ,  20 ,  26  can have a softer support. This in turn results in a reduction of the structure-borne sound since the rail  18 ,  20 ,  26  is decoupled from the sleeper  10 . The support point load is reduced too. 
     To realize the teachings in accordance with the invention, however, it is provided that the intermediate layer  36 ,  38 ,  40  has in respect of its spring properties or rigidity a so-called kinked characteristic. The intermediate layer  36 ,  38 ,  40  therefore has elastic or “soft” properties as long as the maximum permissible or presettable rail stress has not yet been reached. If this rail stress does prevail, the intermediate layer  36 ,  38 ,  40  is “hard”, i.e. has a high rigidity, so that there is no further bending of the rail  18 ,  20 ,  26  and hence no increase in the rail stress. 
     Since a rail can, depending on its geometry, more or less perform the function of a support and hence develop a load-carrying effect, a reduction of the rigidity x of the intermediate layer results when the moment of inertia I x  and the moment of resistance W x  of the rail are increased, i.e. for example when the geometry of a standard UIC 60  rail  18  is altered to the effect that the web  22  is widened and the rail foot  24  merges with a slight curvature into the web  22  in accordance with FIG.  2 . The result of this is that the rail  20  can be mounted more softly without exceeding the maximum permissible rail stress of 70±4 N/mm 2  in particular. Soft mounting means however a further decoupling from the sleeper  10 , with the consequence that the structure-borne sound emitted by the rail  20  is reduced. 
     Even better results are obtained with the filled section rail  26  according to FIG. 3, since the even higher moment of inertia I x  and moment of resistance W x  permit an even softer mounting before the maximum permissible rail stress is attained. 
     The geometry of the rail  20  or that of the filled section rail  26  furthermore has the advantage that the foot  24  or  34  respectively has been changed in its vibration technology compared with the UIC 60  rail  18 , such that when vibrations are excited the emitted sound is not in the undesirable frequency range between 500 and 3000 Hz. The widening or shape alteration of the web  22  of the rail  20  also reduces the airborne sound usually emitted by the web of a Vignol rail. 
     On the basis of the teachings in accordance with the invention, that the rail  18 ,  20 ,  26  is elastically mounted on the intermediate layer  36 ,  38 ,  40  such that under normal wheel loads the maximum permissible rail stress can be reached, but—thanks to the kinked curve of the characteristic—is not generally exceeded, the advantage is obtained that the rail  18 ,  20 ,  26  and the sleeper  10  are decoupled such that undesirable structure-borne sound is prevented. If in addition a filled section rail  26  or a Vignol rail  20  with web  22  of modified vibration characteristics and foot  24  is used in order to largely suppress the emission of airborne sound in the range between 500 and 3000 Hz, the result is an improvement of the ballastless track from the acoustic viewpoint. 
     Taking into account the teachings in accordance with the invention, the result for a filled section rail Vo 1-60 with I x =3760 cm 4 , W x =430 cm 3  and a maximum permissible rail stress of 73 N/mm 2  for the intermediate layer  40  is a rigidity of 10 kN/mm, from which in turn a maximum support point load of 25.3 kN is calculated. These values apply in that working range in which the maximum rail stress is not exceeded. If by contrast the latter is reached, the rigidity of the intermediate layer  40  changes such that the latter is “hard”, i.e. largely non-elastic, so that there is no further bending of the rail. In this “hard” range the rigidity x should be ≧35 kN/mm. 
     These values show that the filled section rail  26  is decoupled from the support layer  40  to an extent that when it is traversed by rolling stock the structure-borne sound of the rail  26  is only transmitted to a minor extent to the sleeper  10  and hence to the substructure.