# Damping and Natural Period Evaluation of Tall RC Buildings Using Full-Scale Data in Korea
## 4 Natural Period and Damping Ratio Identification from Measured Full-Scale Data  
The list of 36 buildings used for ambient vibration measurement is presented in Table 7. As can be noticed from Table 7, 28 out of the 36 buildings are taller than 100 m. The gravitational resistance of buildings No. 1 to No. 10 is entirely provided by the RC shear wall because these are typical mid-rise residential buildings that consist of shear walls without any beams and columns. The gravitational resistance of all other buildings is provided by RC shear walls and moment frames. Building No. 14 is an exception because it is an SRC structure. The 36 measured buildings were selected based on the possibility of the measurement because most of them are privately owned residential buildings. Therefore, the monitored buildings may not be representative of the building stock in Korea. Ambient vibration measurements of all buildings listed in Table 7 were performed using three servo-type accelerometers installed on the top floor, as shown in Figure 2. Three accelerometers were used to detect two translational components and a rotational component of floor motion based on the assumption of rigid diaphragm behavior [17]. A data logger called Netpod 4003 (Keynes Control Ltd., Swallowfield Berkshire, UK) with 24-bit resolution was used to collect measured data. The acceleration measurement range was \(\pm\)0.25g with a sampling rate of 200 Hz, and the measurement duration was at least 30 min. The measured data were digitally filtered using a band-pass filter with cut-off frequencies of 0.01 Hz and 10 Hz to remove signal drifts and high-frequency noises, and the data were subsequently decimated to a 20 Hz signal for efficient numerical data processing. In Figures 3 and 4, the measured 1-min acceleration time histories of Harbor View 1502 and 30-s acceleration time histories of Central Park 103, respectively, are presented. Figure 3 represents the typical acceleration time histories obtained from the ambient vibration measurement on a calm day, while Figure 4 shows the peak acceleration measured on a windy day. It can be seen from Figures 3 and 4 that the accelerations measured in the ambient vibration measurement are very small, with values of less than 1 milli-g. It was reported that the natural frequency and damping ratio are varying values depending on the vibration amplitude, temperature and humidity [18,19], but this variation is not considered in this study. Figure 1: Values of structural damping ratio for RC buildings. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**No** & **Building Name** & **No. of Stories** & **Building Height (m)** & **Location** & **Natural Period (s)** & **Damping Ratio (\%)** \\ \hline
1 & Humanasia 911 & 35 & 104.3 & Seongnam & 1.68 & 0.75 \\
2 & Humanasia 914 & 25 & 75.3 & Seongnam & 1.11 & 0.72 \\
3 & Humanasia 101 & 15 & 44.8 & Seongnam & 0.67 & 0.79 \\
4 & Humanasia 103 & 17 & 50.4 & Seongnam & 0.83 & 0.51 \\
5 & Humanasia 106 & 19 & 56.0 & Seongnam & 0.81 & 0.51 \\
6 & Humanasia 301 & 15 & 44.8 & Seongnam & 0.65 & 0.65 \\
7 & Humanasia 304 & 18 & 53.2 & Seongnam & 0.77 & 0.38 \\
8 & Humanasia 307 & 15 & 44.8 & Seongnam & 0.65 & 1.40 \\
9 & Humanasia 504 & 35 & 104.3 & Seongnam & 1.76 & 0.71 \\
10 & Humanasia 508 & 35 & 104.3 & Seongnam & 1.91 & 0.90 \\
11 & Adelis & 47 & 157.7 & Busan & 2.93 & 0.72 \\
12 & Centrum Park & 51 & 153.0 & Busan & 2.54 & 0.61 \\
13 & Centum star & 60 & 209.6 & Busan & 4.28 & 0.60 \\
14 & NEATT & 68 & 305.0 & Incheon & 4.81 & 0.38 \\
15 & Leaders’ View & 57 & 217.0 & Daegu & 4.44 & 1.22 \\
16 & We’ve & 54 & 182.0 & Daegu & 3.46 & 0.44 \\  
irst World & 64 & 237.0 & Incheon & 5.29 & 0.47 \\
36 & Star City & 60 & 204.0 & Seoul & 4.05 & 0.84 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: List of RC buildings for ambient vibration measurement. Figure 2: Equipment for ambient vibration measurement: (**a**) accelerometer (Kinemetrics Episensor ES-U2) and (**b**) data logger (Netpod 4003, Keynes Control Co.).