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 Bearing structure with reduced vibratory level for railroad trackThe Patent Description & Claims data below is from USPTO Patent Application 20080054086. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNOLOGICAL BACKGROUND [0001]The present invention relates to bearing structures for railroad tracks on a track bed. [0002]A railroad track for a tramway, subway or train always generates vibrations that propagate in and harm the environment. The vibratory levels generated depend on the characteristics of the vehicles transiting on the railroad track and the characteristics of the railroad track bed. For a standard ballasted track, the main frequency of the vibrations generated is approximately 60 Hz. This frequency is determined by the rigidity of the ballast and its under-layer, and by the unsprung mass of the vehicle truck transiting on the railroad track. For a track placed directly on concrete, the main frequency of the vibrations generated is in a range from 40 to 60 Hz, depending on the rigidity of the rail fixation system. This frequency is determined by the rigidity of the rail fixation system and the concrete foundation and by the unsprung mass of the vehicle truck. [0003]On the vibration propagation plane, it is found that a track placed on a rigid soil (for example a rocky soil) results in vibratory levels with lower amplitudes than a track placed on a flexible soil (for example a clay soil). On the other hand, vibrations generated in rigid soil propagate farther (they are less damped) than in flexible soil, which is more shock absorbing. SUMMARY OF THE INVENTION [0004]It is an object of the present invention to provide a bearing structure for railroad track rails that reduces significantly the vibratory level generated by the passage of vehicle trucks transiting on the rails, whatever the road foundation of the railroad track bed. This object is reached according to the invention by a bearing structure for railroad track rails comprising several load distribution plates in a rigid material, disposed side to side on the track bed, below the railroad track, each of these load distribution plates having a surface and thickness predetermined in such a way that its first resonance frequency is greater than the first resonance frequency of the vibrations locally generated in the rails by the passage of vehicle trucks transiting on the railroad track. [0005]The aforementioned load distribution plates are relatively short, rather thick plates that extend on the track bed, below the railroad track. They may be placed on the ground or integrated into the coating of a train or tramway roadway and they may be placed on the foundation of a subway or train tunnel as well. The load distribution plates may be made of concrete, a composite material, or another 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) and they may be butt-jointed with joints that allow free rotation of a load distribution plate with relation to adjacent plates. [0006]Thus, instead of exciting the ground very locally below a vehicle truck transiting on the railroad track, the excitation is distributed over a large surface (without dynamic amplification), with a resulting lower vibratory level. A vibration gain of at least 8 dB is obtained by utilizing such a load distribution plate over a non-rocky conventional soil. This vibratory level reduction is explained as follows: instead of the dynamic stresses of the four wheels of a truck being distributed over 4 m.sup.2 (or 4 times 1 m.sup.2), here the stresses are distributed over a surface of at least 10 m.sup.2 (by considering a load distribution plate that is 4 m long and 2.5 m wide), which gives a vibratory amplitude reduction factor of 2.5 (or approximately 8 dB). This dynamic stress distribution results in a vibratory level of the ground below this load distribution plate that is markedly less than that which would be produced without this load distribution plate. [0007]Each load distribution plate is dimensioned such that its first resonance frequency is greater than approximately 1.4 times the first resonance frequency of vibrations locally generated in the rails by the passage of a vehicle over the railroad track rails. 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 plate must be greater than 80 Hz. Therefore, when a vehicle passes on the railroad track above a load distribution plate, the plate is deformed in conformance with its static deformation without significant dynamic amplifications due to the resonances. In the example cited above, to arrive at a first resonance frequency of the load distribution plate that is greater than 80 Hz having a concrete slab with a length of 4 m (and not wider than 4 m), it must have a thickness of at least 400 mm. [0008]Each load distribution plate in the bearing structure according to the invention may be made in the form of a single beam or any other suitable form provided that it has a first resonance frequency (torsion or flexion) greater than the first resonance frequency of the vibrations locally generated by the passage of a vehicle transiting on the rails of the railroad track. The load distribution plates may be utilized under normal tracks (in alignment and in curves), under switches and crossings or under ballast. [0009]Other details and special features of the invention will be apparent from the following description and the attached drawings, which illustrate examples of embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0010]FIG. 1 shows a longitudinal section in a railroad track bearing structure according to the invention, with ballast; [0011]FIG. 2 is a plan view showing the load distribution plates of FIG. 1; [0012]FIG. 3 shows a longitudinal section in a railroad track bearing structure according to the invention for fixing rails on concrete blocks; [0013]FIG. 4 is a plan view of the railroad track bearing structure from FIG. 3; [0014]FIG. 5 shows a plan view of a railroad track bearing structure according to the invention for integrating rails in concrete load distribution plates; [0015]FIG. 6 is a plan view according to line A-A of FIG. 5; [0016]FIG. 7 illustrates several possible cross sections for the load distribution plates. [0017]In these drawings, the same reference numerals identify identical or equivalent elements in the bearing structure. DESCRIPTION OF EMBODIMENTS OF THE INVENTION [0018]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. [0019]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. [0020]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 m.sup.2) 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 m.sup.2 (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). Continue reading... Full patent description for Bearing structure with reduced vibratory level for railroad track Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Bearing structure with reduced vibratory level for railroad track patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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