# Research on Environmental Vibration Induced by High-Speed Maglev Transportation
## 3 Guideway Structure Vibration  
While a maglev train is running, a vehicle-track-coupled vibration propagates from the functional parts to the girder and then to the surrounding environment through the bearing and column. In order to determine the environmental vibration influence of a maglev train, the vibration propagation law in guideway structures should be studied first. The construction of railway lines through viaducts has many advantages, such as suitable ground conditions, saving ground space, being suitable for prefabrication and assembly, and reducing noise and vibration, so this approach is widely used in urban railway transit. As the substrata along the Shanghai maglev line are of loose deposits of the fourth period, mainly composed of saturated clay, silt, and sandy soil, all of the guideway girders are supported on viaducts using pile foundations [1]. While maglev trains are running, vibrations generated by vehicle-track interactions cannot directly propagate into the surrounding environment but must first pass through the bearing and column. Although it has been proven that viaduct structures can significantly reduce the vibration generated by wheel-track transit, how well it works in terms of maglev transportation still needs to be studied. In this research, the test points along the path of vibration propagation included the inner functional part (point A), the end of the girder (points C and D), the upper board of the bearing (point E), the lower board of the bearing (point F), and the central area of the ground foundation (point G). The acceleration time history and frequency spectra calculated using fast Fourier transformation (FFT) of these test points in order of altitude, from high to low, are listed in Figure 6 (in sequence: points A, C, D, E, F, and G). Observing the time histories above, with the propagation of the vibration, the peak acceleration reduces from around 10 m/s\({}^{2}\) at the inner functional part to around 0.15 m/s \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number** & **Time** & **Route** & **Girder Number** \\ \hline
1 & 15:23 & Longyang–Pudong & A \\ \hline
2 & 15:26 & Pudong–Longyang & B \\ \hline
4 & 15:43 & Longyang–Pudong & B \\ \hline
5 & 15:46 & Pudong–Longyang & A \\ \hline
7 & 16:03 & Longyang–Pudong & A \\  & 16:06 & Pudong–Longyang & B \\ \hline
8 & 16:23 & Longyang–Pudong & B \\  & 16:26 & Pudong–Longyang & A \\ \hline
9 & 16:43 & Longyang–Pudong & A \\  & 16:46 & Pudong–Longyang & B \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Timetable of trains running throughout the test procedure. at the center of the ground foundation; the attenuation along the guideway structure is quite obvious. The vibration at the end of the girder (subgraph for points C and D) is quite large when a maglev train has just entered or just left the guideway girder. The peak acceleration can be as large as 10 m/s\({}^{2}\), sometimes even up to 20 m/s\({}^{2}\), but then it turns to a steady state at around 2-4 m/s\({}^{2}\). As the guideway girders are mainly simply supported beams, the level and offset between adjacent girders, as well as the dynamic deformation induced by the running maglev train, lead to irregularity between the girders and cause these impacts. When comparing the time history for the upper and lower boards of the bearing (subgraph for points E and F), it can be seen that, after the vibrations propagate through the bearing, although the peak acceleration does not change too much, the time history becomes smoother, which means that the bearing plays the clear role of a wave filter. As for the vibrations at the top and bottom of the column (subgraph for points F and G), it can be seen that the vibration is reduced by over 75% after propagating through the 10 m high column. This attenuation phenomenon proves that even the dynamic load of maglev transportation is different from that of traditional wheel-track transformations, and the viaduct structure is still useful to reduce the ground vibration level.