## 4 Experimental Modal Parameters Analysis
### Measured Modal Frequency under Different Wind Speeds
#### 4.2.1 Identification Method of Modal Parameters
This paper firstly sets reasonable band-pass filtering for the first three-order frequencies of the measured data, and the band-pass range of filter along the X and Y axes was determined as \(f\in(f_{i}-0.08f_{i},f_{i}+0.08f_{i})\), where \(f_{i}\) is the frequency identified by spectrum peaks with the time duration of 10 min, it can be separating out the first three-order frequency resonance signals in the high-rise building, and then the frequency \(f\) was identified according to the free vibration attenuation curve, whereas the circumference ratio was calculated by the formula \(\omega=2\pi f\). Figure 17 is the first-order free attenuation curve of several samples calculated by RDT along the transnational and torsional directions when the basic time duration is 10 min. 2.2 Calculation Method of Fundamental Frequencies of High-Rise Buildings under Different Wind Speeds  
The natural frequency of a high-rise building is the natural attribute of structural vibration. The natural frequency is an important index to judge whether the structural stiffness, quality, and stiffness are reasonable. The existing codes estimate the fundamental frequency of high-rise buildings, but they do not evaluate the impact of a strong typhoon on the fundamental frequency of high-rise buildings. According to the measured data of natural frequency of super high-rise buildings under different wind speeds, the most direct correlation factor causing the change in modal parameters of high-rise buildings is the wind speed. The samples were selected from all the measured data of typhoon Sarika. Because the coupling effects of structures would not remain the same in different wind speeds, the first three-order modal frequencies along the X axis, Y axis, and torsional direction under different mean wind speed were obtained based on the sufficient experimental data to analyze the relationship between the first three-order modal frequencies and wind speed. It can be known from Figure 18 that the first three-order modal frequencies along the X and Y axes and the torsional direction decrease linearly as the mean wind speed increases, which explains that the coupling effects between wind and structures are more obvious as wind speed increases, and those effects have great influences on the modal frequencies of structures, thus needing to be emphasized in wind-resistant designing of high-rise buildings. It also can be concluded from the comparisons of frequencies along the Y axis and those along the torsional direction shown in Figure 18 that their sizes and development trends are almost the same. Therefore, the frequencies in the torsional direction of high-rise buildings were close to those along the Y axis. Figure 17: The first-order free vibration attenuation curve along the translational and torsional directions identified by RDT: **(a)** free vibration attenuation curve along the X axis; **(b)** free vibration attenuation curve along the Y axis; **(c)** free vibration attenuation curve along the torsional direction. The fundamental natural period, which is the important standard to judge the reliability of the stiffness and to evaluate whether mass matches with the stiffness of structures, is the inherent basic dynamic characteristic of high-rise buildings.