## 3 Train-Bridge System Aerodynamic Characteristics
### The Bridge Aerodynamic Characteristics
#### 3.2.2 Wind Pressure Distribution on Bridge  
As shown in Figure 11, the bridge is divided into 12 zones based on the variation of the cross-section. Zone I is the windward side, zones II-IV are the bottom side, zone V is the leeward side, and zones VI-IX are the top side. For the bare bridge, positive wind pressure occurs throughout the windward side, with the max positive pressure appearing at measuring point 2 and the wind pressure coefficient reaching 0.94. The entire bottom and top of the bridge exhibit negative pressure, with a significant negative pressure zone appearing at the front edge of zones II-III on the bottom and the front edge on the top. The extreme negative pressure coefficients are \(-1.56\) and \(-2.03\), respectively, while the negative pressure decreases gradually from the rear to the leeward side. When WGBs are installed on the bridge, the positive pressure on the windward side decreases, the negative pressure on the bottom side increases, and the strong negative pressure zone on the bridge surface is suppressed. Meanwhile, the negative pressure decreases, leading to an increase in bridge \(C_{H}\) and a decrease in \(C_{V}\). When there are trains on the bridge, the wake width of the train-bridge system increases, and the extreme wind pressure coefficient in zone IX changes from \(-0.83\) to \(0.53\) when perforated wind barriers are installed. The pressure in zones VIII and VII (the ballast) is enhanced due to the acceleration of the train's pressure airflow, especially when the train is located on the windward side of the track, and the extreme negative pressure increases from \(-1.03\) to \(-1.45\). Compared to the vertical wind  
Figure 10: Aerodynamic coefficients of bridge and barrier: (**a**) without train; (**b**) the train is located windward; (**c**) the train is located leeward. Figure 9: Effect of WGB parameters on HST fluctuating pressure (leeward): (**a**) angle of the main deflector plate \(\theta_{1}\); (**b**) width of the WGB root \(B_{1}\); (**c**) size of the upper deflector angle \(h_{1}\). barrier, the installation of WGB can suppress the strong negative pressure on the ballast and reduce the influence of train position on the wind pressure distribution of the bridge. As shown in Figure 11, when there is no train on the bridge and various types of WGB are installed, the overall distribution of wind pressure on the bridge is consistent: the entire windward surface shows positive pressure, with the max positive pressure appearing at the 2# measuring point on the windward surface; except for the 8#, 9#, 14#, and 15# measuring points in the corner area where the negative pressure is relatively small, the entire bottom surface shows strong negative pressure; the leeward side of the bridge shows relatively weak negative pressure, and the max negative pressure on the bridge surface appears near the 22# measuring point at the rear corner of the bridge, while the minimum negative pressure appears on the side of the windward track bed at the 38# point. From Figure 12, it can be seen that adjusting \(\theta_{1}\) and \(h_{1}\) has almost no effect on the surface wind pressure distribution of the bridge. When \(B_{1}\) is increased, the airflow passing through the bottom of the wind barrier is reduced, the forward flow on the windward surface is slowed down, and the wind pressure on the windward surface is reduced. At the same time, the separation of the airflow in the system accelerates, resulting in an increase in negative pressure on the bottom surface and bridge surface. Figure 11: Wind pressure distribution on the bridge: (**a**) with or without wind barriers (for upstream trains); (**b**) installing a WGB for different train and bridge combinations in Case 2; (**c**) bridge pressure zoning; (**d**) installing a WGB for different train and bridge combinations in Case 4.