# Wind Load Characteristics of Wind Barriers Induced by High-Speed Trains Based on Field Measurements
## 4 Results and Discussion  
### Measurement Data  
The original measurement data includes both the train-induced fluctuating pressure and the environmental wind pressure. However, the effects of environmental wind on the fluctuating pressure on the barrier can be ignored when the its speed is below 2 m/s [25]. Therefore, the test results presented in this study were selected to satisfy such environmental wind speeds during the passage of the  
Figure 5: Schematic diagram of the wavelet transform (WT) decomposition process. high-speed trains. The wind pressures of three measurement points (point 2, point 7, and point 9) under train-induced wind, with a running speed of 275 km/h, are illustrated in Figure 6. It can be seen from Figure 6 that the variations in wind pressure at each measurement point were basically the same when the high-speed train passed the wind barrier. The pressure variation induced by the slipstream of the high-speed train was dynamically processed in the time domain. The positive value (push effect) during the passage of the head vehicle, and the negative value (pull effect) during the passage of the tail vehicle could be observed, and were similar to the results in References [25; 31]. The pressure caused by train-induced wind could be preliminarily divided into three sections, as shown in Figure 6. Section 1 was mainly influenced by the \"head wave effect\". The positive wind pressure reached the maximum value when the head vehicle was closest to the test point. This was because of train-induced positive wind pressure acting on the inner surface of the barrier. The positive peak occurred at the arrival of the train noise. Then, the wind pressure dropped to a negative value instantaneously when the head vehicle passed the test point. Therefore, a complete pressure wave was generated by the head vehicle, namely the \"head wave effect\". Section 2 showed that the negative pressure increased suddenly and then kept a relative steadiness when the middle vehicles passed through the test points. The relative stable performance of pressure in Section 2 was because of the uniform cross section of the train. However, the effect of environment wind, the complex structures of bogies, and inter-carriage gaps resulted in some small fluctuations. Section 3 was mainly influenced by a \"tail wave effect\". The wind pressure dropped to the negative pressure extremum when the tail vehicle was closest to the test point. However, the wind pressure increased instantaneously to the positive pressure extremum after the tail vehicle passed the test point. Thereafter, the pressure dropped to zero. It should be noted that the pressure amplitudes induced by the \"head wave effect\" were slightly larger than those induced by the \"tail wave effect\" for each test point. Thus, the train-induced wind generated two impacts with opposite directions on the wind barrier. This can cause oscillations of the wind barrier in the horizontal direction and wave movements in the longitudinal direction (the train's running orientation). Pressure amplitude is usually adopted to describe the characteristics of the transient wind load. Figure 7 shows the pressure amplitudes of all points under the train, running at a speed of 275 km/h. It can be seen that the maximum pressure amplitude appeared at point 9. The elevation of point 9 was parallel to the rail surface. Since the top of wind barrier has no boundary condition and the bottom of the wind barrier is mostly sealed to the bridge deck, the pressure amplitude decreased rapidly with an increase in the test point height. The maximum pressure amplitude was about 582 Pa, which is approximately three times that of the minimum pressure amplitude. Figure 6: Measured wind pressure with respect to different test points (train speed = 275 km/h).