## 5 Evaluation Method of Wind Barrier Arrangement
### Evaluating Different Wind Barrier Arrangements near a Bridge Pylon Zone  
According to the analysis in Section 4, the wind environment above bridge deck at the influencing zone of the pylon is unfavorable for vehicle stability under crosswinds. Setting wind barriers in a certain range around the pylon is an effective countermeasure to improve the wind environment above the bridge deck and the driving safety. To explore the improvement effect of wind barriers, three kinds of wind barriers were proposed. The cross section of wind barriers is a circular arc, and the barriers with the width of 220 mm are set in a curved shape vertically. The distance between the centers of the adjacent bars is 420 mm. Figure 18 shows the layout of the wind barriers. For all schemes, H1 = 1.3 m, H2 = H3 = H4 = 0.84 m. Details of L are shown in Table 1.  
The numerical simulation of wind speed above the bridge deck in the pylon zone under different conditions is carried out, and the influence coefficients at different special points are calculated. The distributions of the \(\lambda_{s}\) under different conditions are shown in Figure 19.  
From Figure 19a-e, it can be seen that the wind speed increases significantly outside the pylon without wind barriers. After the wind barriers were installed, the velocity increase outside the pylon was effectively eliminated, and the changing gradient becomes more and more smooth.  
The Sutong Bridge is designed for driving speeds of 100 km/h, with the speed limits for safe operation being 80 km/h on a normal day, and 60 km/h on a windy day. The results of \(K\) under different conditions are shown in Table 2. By analyzing the data in this table, it can be seen that \(K\) dramatically improves after the installation of wind barriers and that this increase is proportional to the wind barrier length. However, up to a certain threshold, additional lengthening of the wind barriers no longer generates any further effects. The values for \(K\) in Schemes 2 and 3 are larger than 2.5, which indicate a good wind environment for the operating stability of a vehicle in the crosswind. With all factors considered, Scheme 2 was adopted for Sutong Bridge, which is more economical, as Figure 20 shown. Figure 19 shows the influence coefficients in the longitudinal direction, and the influence coefficient ratio \(R\) is shown in Table 2. It can be seen that \(R\) is close to 1 in Schemes 2 and 3, which means these two schemes are optimal in terms of their wind barrier arrangement.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & L* & L1 & L2 & L3 & L4 \\ \hline Scheme 1 & 25 & 7 & 6 & 6 & 6 \\ Scheme 2 & 41 & 11 & 10 & 10 & 10 \\ Scheme 3 & 57 & 15 & 14 & 14 & 14 \\ \hline \hline \end{tabular} where L* is the total length outside the pylon; L1 is the length of nine-bar wind barriers area; L2 is the length of seven-bar wind barriers area; L3 is the length of five-bar wind barriers area; L4 is the length of three-bar wind barriers area.  
\end{table}
Table 1: The concrete size of wind barriers (unit m).  
Figure 18: Wind barriers layout.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Condition**} & \multirow{2}{*}{\(\lambda_{\text{s}}\)} & \multirow{2}{*}{**R**} & \multirow{2}{*}{\(\mathbf{L_{d}}\) (\(\mathbf{m}\))} & \multicolumn{3}{c}{**K**} \\ \cline{5-7}  & & & & \(\mathbf{V_{1}}^{*}\) & \(\mathbf{V_{2}}\) & \(\mathbf{V_{3}}\) \\ \hline C1 & 1.304 & 1.427 & 16.00 & 0.7 & 0.9 & 1.2 \\ C2 & 1.114 & 1.219 & 20.00 & 0.9 & 1.1 & 1.5 \\ Scheme 1 & 1.009 & 1.104 & 40.00 & 1.8 & 2.3 & **3.0** \\ Scheme 2 & 0.965 & **1.056** & 56.00 & **2.5** & **3.2** & **4.2** \\ Scheme 3 & 0.918 & **1.004** & 72.00 & **3.2** & **4.1** & **5.4** \\ \hline \hline \end{tabular}
\end{table}
Table 2: The concrete size of wind barriers.  
Figure 19: The influence coefficient \(\Lambda\)s.