RTR Eurailpress

RTR 4/2010 13 Frequencies of the ballasted track n values in the range between 0 to 1000 Hz. Now we are happy to see that in Fig. 12 a possibility is hidden to simplify this operation, as it is very helpful for the design of ballasted tracks if we know the mode free limits. So the coincidence of excitation and eigenfrequencies may be avoided. At the upper limit of the 1st mode free area (Nr. 1 in Fig. 12) there is the mode A in Fig. 10. At the lower limit of the 2nd mode free area (Nr. 2 in Fig. 12) there is the mode K in Fig. 10. And at the upper limit of the 2nd mode free area (Nr. 3 in Fig. 12) there is the mode L in Fig. 10. Answering the question that we had in the beginning, if everything is done correctly, we have to say: The ballasted track that we have on high speed tracks at present guaranties strong wear but does not prevent it. 6 Simplified calculation of the mode free limits In order to find the 3 limits of the mode free areas we had to calculate all the eigenabout 80 Hz. This frequency is loosening the density of ballast [2]. The strong 3rd wheel harmonic of out of round wheels is uncontrolled occurring in service also. Both effects together are probably the cause of the frequent, unintentional irregular changes of the track position. The 98 Hz of the 4th wheel harmonic are close to the 98.7 Hz where the greatest amplitudes arise in the front wave of the unloaded track in Fig. 10E. Similarly unwanted are the 123 Hz of the 5th wheel harmonic, which are close to the 125.4 Hz of the Fig. 10H where the sleepers have the greatest amplitudes. There they also have a strong interaction with the brake discs of the wheel set. The practical experience with permanent ways shows that already existing irregularities of the track position are contributing to more intensive deterioration of the track position. This experience is confirmed by the results here because of the resonances. But it could be worse, if we did not have the cost free transfer of energy by the half space damping at small frequencies, as the damping of the rail fastenings is poor. In Fig. 12 in combination with Fig. 1 we can see, that unfortunately for a velocity of 250 km/h the eigenfrequencies of the unloaded ballasted track with concrete sleepers are placed in the limits of the excitation frequencies. Fig. 13: Mechanical models for the calculation of the mode free limits.

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