The modal frequencies and effectiveness in vibration reduction of direct-fixation track on viaduct

Replacing conventional ballast track, direct-fixation tracks (DFTs) are supposed to generate less noise and vibration; however, the authorities obtain more complaints by metropolitan residents. In order to investigate the modal frequencies of DFTs, field tests were performed on viaduct with I-shape concrete girder on Western Trunk Line of Taiwan Railway Administration (TRA). Experimental modal analysis (EMA) was first conducted to capture the natural frequencies of DFT and frequency response function of the system. Vehicular vibrations were then measured to obtain the insertion loss of elastic baseplate and the frequency spectrum to reveal the effectiveness of DFTs in vibration reduction. The free vibration of the bridge after vehicle passing through was also collected to verify its nature frequencies. According to the results of field tests, the dynamic behavior of elastic baseplate should be considered in the system. To ensure those results, a finite element DFT model was established and given by the same hammer excitation from EMA. The findings from field tests match our finite element analysis, which have demonstrated that the major frequencies of DFT are not only close to 100 Hz and 630 Hz, respectively, but the mass of the elastic baseplate should not have been overlooked in simulation.