# Full-Scale Measurements of Wind Characteristics on a High- Rise Building during Typhoon Sarika
## 3 Wind Characteristics of Typhoon Sarika
### Turbulence Intensity and Integral Scale  
#### 3.3.1 Turbulence Intensity  
Turbulence intensity (\(I_{u}\), \(i=u,v\)) is defined as the ratio between the standard deviation of fluctuating wind (\(\sigma_{i}\)) and mean wind speed (\(\overline{U}\)) for a given sample duration. Figure 7 shows the relationship of the 10-min variations longitudinal and lateral turbulence intensities (\(I_{u}\) and \(I_{v}\)) with respect to mean wind speeds and directions (\(\alpha\)). The measured results show that the 10-min longitudinal and lateral turbulence intensities decrease with the increasing mean wind speed, and the reduction rate of the \(I_{u}\) and \(I_{v}\) drops after the 10-min mean wind speed reaches an absolute value (\(\overline{U}\) = 10 m/s). The measured 10-min longitudinal and lateral turbulence intensities \(I_{u}\) and \(I_{v}\) are obviously correlated with wind direction. It is notable that \(I_{u}\) and \(I_{v}\) reach larger values along the 10-min wind directions of 30\({}^{\circ}\) and 190\({}^{\circ}\), while inclining toward smaller values along the 10-min wind directions within 100\({}^{\circ}\)-160\({}^{\circ}\). There are numerous mid-high-rise buildings located in the wind direction of 30\({}^{\circ}\) and 190\({}^{\circ}\), and the peak turbulence intensity appears along those wind directions due to the severe interference to the wind field. And there are numerous low-rise buildings along the wind direction of 100\({}^{\circ}\)-160\({}^{\circ}\); thus, the lowest turbulence intensity appears along those wind directions due to slight interference. According to the calculation formula of turbulence intensity along height distribution in Chinese code (GB50009-2012), the formula can be expressed as:  
\[I_{z}(z)=I_{10}\Big{(}\frac{z}{10}\Big{)}^{-\alpha} \tag{7}\]  
where \(\alpha\) is terrain roughness parameters index, the parameters \(\alpha\) corresponding to categories A, B, C, and D can be prescribed as 0.12, 0.15, 0.22, and 0.30, respectively. The value \(z\) is the erection height of anemometer. The value \(I_{10}\) is turbulence intensity at the height of 10 m corresponding to categories A, B, C, and D of terrain roughness, which can be prescribed as 0.12, 0.14, 0.23, and 0.39, respectively. Equation (7) can be used to calculate the turbulence intensity at a height of 115 m with respect to four categories of terrain roughness are 8.95%, 9.71%, 13.4%, and 18.8%, respectively. The measured turbulence intensity with a 10-min interval is 15-40% during Typhoon Sarika, which indicates that the measured wind field characteristic is greatly subject to the interference of the ambient condition, thus the category of terrain roughness for most of the inflow wind is D. The measured turbulence intensity is 10% along the critical wind directions of 160\({}^{\circ}\) is close to category A of terrain roughness. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time Steps** & **Stationary Samples** & **Non-Stationary Samples** & **The Ratio of Non-Stationary Samples** \\ \hline
30 s & 198 & 22 & 10.00\% \\
20 s & 190 & 30 & 13.64\% \\
10 s & 172 & 48 & 21.82\% \\
3 s & 113 & 107 & 51.36\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The stationarity test results of Typhoon Sarika at different time steps. In summary, the turbulence intensity of fluctuating wind closely relates to the ambient condition disturbance and terrain roughness categories. The measured turbulence intensity in the inflow-wind area is the lowest when terrain roughness is category A. Turbulence intensity decreases with the increasing mean wind speed in the same terrain roughness categories, and the longitudinal turbulence intensity are generally more significant than lateral turbulence intensities.