Dynamic behaviour of twin single-span ballasted railway viaducts — Field measurements and modal identification

This paper presents the results of experimental measurements on a number of existing small to medium single span ballasted railway bridges in Austria. These bridges were selected for dynamic field measurements following a preliminary numerical evaluation that identified very high vertical accelerations. From the dynamic measurements it was possible to conclude that: (i) the damping due to friction between ballast particles and the friction in the supports plays an important role in the evaluation of maximum accelerations and (ii) the first natural frequencies of the bridges vary according to the amplitude of vibration, that is, increasing vibration amplitudes correspond to a decrease of the first natural frequency in a consistent way for all investigated bridges. Calibrated FE models for these bridges confirmed the experimental conclusions.