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The rated suspension gap of a low-to-medium-speed maglev train with electromagnetic suspension is normally 8-10 mm. However, while either passing over a bridge or being stationary on one, the maglev train deforms the bridge and therefore alters the suspension gap. Hence, a problem arises due to coupled vibrations between the maglev train and its supporting bridge. In the study reported here, field experiments were conducted on the Chinese Changsha maglev line, which was the first commercial low-to-medium-speed maglev line in China. The focus is on two types of prestressed double-track concrete bridges on the maglev line. One is a simply supported girder with a span of 25 m, while the other is a continuous girder designed as 25 þ 35 þ 25 m. The accelerations and vertical dynamic deflections of the two bridges at midspan were measured while a five-module low-to-medium-speed maglev train with electromagnetic suspension either passed over or was stationary on either bridge, as were the accelerations of the car body and the suspension frame. The basic dynamic characteristics of the two bridges are analysed and compared with those of bridges in various typical maglev lines. The vibration characteristics of the two bridges, the car body and the suspension frame are studied in the time and frequency domains for the maglev train running at normal speeds, low speeds and when stationary. The influences of the speed on the dynamic characteristics are discussed. Some comparisons with other studies are also carried out, including the effects of bridge parameters on the coupled vibrations and the running stability of a low-to-medium-speed maglev and a CRH2C wheel/rail train. Significant conclusions are drawn from the analysis: increasing the rigidity and mass of the bridge can significantly reduce its vibration; increasing the span and deflection of the bridge increases the vibrations of the car body and the suspension frame; the dynamics of the maglev vehicle and bridges are different when the maglev train runs at normal speeds (more than 30 km/h), low speeds (less than 30 km/h) and when being stationary. The running stability of a low-to-medium-speed maglev train is better than that of a CRH2C high-speed train. The present study provides a test basis for further research on the mechanisms for coupled vibrations of maglev train-bridge systems.

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The low-to-medium-speed maglev train is stably suspended near the rated suspension gap. The suspension force acts directly on the track and is transmitted to the bridge. The maglev track structure is novel, and the influence mechanism of the track structure on the coupled vibration of the maglev train-bridge system is unknown. Therefore, in this study, we propose vertical dynamic interaction models of the low-to-medium-speed maglev train-bridge system and the low-to-medium-speed maglev train-track-bridge system to analyse the influence mechanism of the maglev track structure on the vertical dynamic interaction of the low-to-medium-speed maglev train-bridge system. The vibration characteristics of the F-rail and the influence mechanism of the track structure on the dynamic responses of the bridge are discussed in detail. The study verifies that the local deformation of the F-rail is self-evident and cannot be ignored. In addition, the influence of the F-rail on the dynamic interaction of the maglev train-bridge system is mainly reflected in two aspects: first, the vibration of the bridge in the high-frequency band increases due to the high frequency and intensive local vibration of the F-rail itself. Second, the vibrations of the bridge and the F-rail in the low-frequency band increase due to the periodic irregularities caused by the local deformation of the F-rail. In this study, we consider the vertical dynamic interaction model of the low-to-medium-speed maglev train-track-bridge system.