BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a longitudinal section in a railroad track bearing structure according to the invention, with ballast;
FIG. 2 is a plan view showing the load distribution plates of FIG. 1;
FIG. 3 shows a longitudinal section in a railroad track bearing structure according to the invention for fixing rails on concrete blocks;
FIG. 4 is a plan view of the railroad track bearing structure from FIG. 3;
FIG. 5 shows a plan view of a railroad track bearing structure according to the invention for integrating rails in concrete load distribution plates;
FIG. 6 is a plan view according to line A-A of FIG. 5;
FIG. 7 illustrates several possible cross sections for the load distribution plates.
In these drawings, the same reference numerals identify identical or equivalent elements in the bearing structure.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
By referring to FIGS. 1 and 2, an example of a railroad track bearing structure according to the invention with ballast may be seen. The railroad track bearing structure, designated in its entirety by the reference 10, comprises cross ties 11 on which the rails (not represented) are fixed in the usual manner, and ballast 12. In conformance with the invention, a set of dynamically rigid load distribution plates 13 extend below the ballast, which plates themselves rest on the ground of the track bed 14. The load distribution plates 13 are relatively short, rather thick plates, that are disposed end-to-end on the ground, below the ballast. They may advantageously be butt-jointed with joints that allow the free rotation of a plate with relation to adjacent plates. Each load distribution plate 13 has a surface and thickness predetermined in such a way as to present a first resonance frequency that is greater than the first resonance frequency of the wheel/rail system. This latter resonance frequency is determined by the rigidity of the ballast and by the unsprung mass of the vehicle truck transiting on the railroad track. In general, the first resonance frequency of the vibrations locally generated by the passage of a vehicle transiting on the railroad track is below 80 Hz.
To be effective, each load distribution plate must have a first resonance frequency greater than approximately 1.4 times the first resonance frequency of the vibrations locally generated in the rails by the passage of a vehicle transiting over the railroad track. In the case where this first resonance frequency of locally generated vibrations is 57 Hz, for example, the first resonance frequency of the load distribution plates must be greater than 80 Hz. Therefore, when a vehicle passes on the railroad track above a load distribution plate, the latter is deformed in conformance with its static deformation, without significant dynamic amplifications due to the resonances. To arrive at a first resonance frequency of the load distribution plate greater than 80 Hz with a concrete slab of 4 m long (and not wider than 4 m), for example, each load distribution plate must have a thickness of at least 400 mm.
With the bearing structure of the invention, the dynamic stresses generated by the passage of four wheels of a truck over a section of track are thus distributed over the surface of the load distribution plate situated below said track section instead of the stresses being applied very locally (4 times 1 m2) on the ground. The result is a lower vibratory level exciting the ground. By utilizing a load distribution plate 13 with a surface of at least 10 m2 (by considering a load distribution plate that is 4 m long and 2.5 m wide) over a conventional non-rocky soil, the vibratory amplitude applied to the soil is reduced by a factor of 2.5 (or approximately 8 dB).
The load distribution plates 13 may be made of concrete, a composite material or other material capable of distributing the loads of vehicles intending to transit on the railroad track. They may be fabricated on site or may be prefabricated (modules).
In the railroad track bearing structure according to the invention, the load distribution plates 13 may also be provided for the direct fixation of rails on concrete through any rail fixation system (discrete or continuous).
FIGS. 3 and 4 illustrate an example of embodiment of the invention in which the load distribution plates 13 are provided for the direct fixation of rails by means of discrete rail fixation systems 15 that are fixed on the load distribution plates 13. In this embodiment too, the load distribution plates 13 are relatively short, rather thick plates disposed end-to-end on the ground 14 and they may be connected by joints that allow the free rotation of a plate with relation to adjacent plates. Also, they may be fabricated on site or may be prefabricated (modules) and they may be integrated in the roadway pavement.
FIGS. 5 and 6 represent an embodiment of the railroad track bearing structure according to the invention in which the relatively short, rather thick load distribution plates 13 disposed end-to-end on the ground 14 comprise grooves 13A in which the rails (not represented) may be integrated. Also, the load distribution plates may be connected by joints that allow the free rotation of a plate with relation to adjacent plates. Such load distribution plates may be fabricated on site or may be prefabricated (modules) and they may be integrated in the roadway pavement.
The railroad track bearing structures according to the invention may be utilized under normal tracks (in alignment and in curves) and under switches and crossings as well.
As indicated above for the case of a ballasted track, each load distribution plate must have a surface and thickness predetermined in such a way that its first resonance frequency is greater than 1.4 times the first resonance frequency of the vibrations locally generated in the rails by the transit of a vehicle on the railroad track. The resulting behavior of the load distribution plates and the reduction in vibratory amplitude are the same as in the case of a ballasted track.
Each load distribution plate may be made in the form of a single beam as illustrated in FIG. 7A or any other suitable form provided that it has a first resonance frequency greater than the first resonance frequency of the vibrations locally generated in the rails by the transit of a vehicle on the railroad track, as indicated above. FIGS. 7B to 7D illustrate some examples of cross sections for load distribution plates 13. FIG. 7B shows a section comprising a bearing plate 13 with lateral sides 13B which extend to the bottom of the bearing plate. FIG. 7C shows a section that differs from that of FIG. 7B by the presence of a longitudinal rib 13C. Several ribs may also be provided. FIG. 7D shows a section in which plate 13 comprises grooves 13A intended to receive the rails of the railroad track.
Patent Application
20080054086
