PSI - Issue 5

Pavel Ryjáček et al. / Procedia Structural Integrity 5 (2017) 1051 – 1056 Ryjacek/ Structural Integrity Procedia 00 (2017) 000 – 000

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The EN 1990 gives the maximal allowed value of the vertical acceleration as 3,5 m·s -2 , which is based on the requirement for the train and ballast stability and sufficient contact between train and the rail. The measured data were evaluated for the frequency interval between 0,5 Hz and 100 Hz. The peak acceleration during the test was:  0,87 m·s -2 in the ¾ of the span for speed 90 km/h,  1,00 m·s-2 on the second superstructure in the ¾ of the span during passing of the real train. All of those values are smaller, than 3,5 m·s -2 required by EN 1990. Regarding the lateral vibrations, the peak accelerations were: However, there is no limit for the lateral vibrations. It quite interesting, that they are significantly higher than vertical vibrations. It is mainly the impact of the small skew angle. The real damping values were evaluated from the vibration of the bridge after the train passed it. For the f (2) = 2,47 Hz the relative damping was  = 1,1 %, for the f m = 8,5 Hz then  = 0,8 %. It can be seen, that the damping is slightly bigger than the value, used in the analysis and significantly bigger than the value from EN 1991-2. The more appropriate way is to assume the damping of the ballast as well as an additional damping The dynamic factor for the main superstructure was δ obs = 1,031, which is bigger than the dynamic factor in the EN 1991-2 ( δ obs = 1,0) – however the difference is very small. The main conclusions of the dynamic load test are that the measured shapes and frequencies correspond to the results of the model and confirmed the accuracy of the chosen damping and the mass or stiffness of the bridge. The dynamic test allowed to verify the safe behaviour of the bridge, which is rather unusual. It shows, that even for such a large bridge, the analysis of the natural frequencies should be done for the fixed bearings in the model, even if they are movable. The parametric study shows that (if possible) the skew angle of railway bridges with slender hangers should be kept at least less than 60° in order to keep the hanger vibrations in the reasonable level without other structural modifications. 4. Conclusions  1,38 m·s -2 in the ½ of the span for speed 70 km/h,  0,98 m·s -2 on the second superstructure in the ¾ of the span during passing of the real train.

Acknowledgements

Research reported in this paper was supported by COST CZ (LD) project of Ministry of education, youth and sports LD (No. LD15127).

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