# Study on Impact-Echo Response of Concrete Column near the Edge
## 4 Result Validation  
The column size in the above test and simulation was 700 \(\times\) 700 mm. In order to verify that the reduction of predominant frequency is a common phenomenon in the edge region of concrete columns and to determine the relationship between the region's influence range and the column's size, concrete columns with cross-section sizes of 400 \(\times\) 400 mm and 1000 \(\times\) 1000 mm were simulated and calculated. Table 4 is the detection data of the 400 \(\times\) 400 mm column. The frequency change trend is shown in Figure 9.  
According to the analysis results of the receiving point signal, when the impact is loaded at each interval of 1 cm in the range of the 400 \(\times\) 400 mm column distance edge mutation, the predominant analytical frequency of the signal at 4-8 cm from the edge is 4.027 kHz and the predominant analytical frequency of the signal at 9-11 cm from the edge is 4.515 kHz. The mutation point is 9 cm from the edge. Within this range, the amplitude of frequency 4.027 kHz gradually decays from 0.420 \(\times\) 10\({}^{-6}\) mm to 0.328 \(\times\) 10\({}^{-6}\) m, and the amplitude of frequency 4.515 kHz gradually increases from 0.311 \(\times\) 10\({}^{-6}\) m to 0.326 \(\times\) 10\({}^{-6}\) m. It can be seen that the frequency 4.027 kHz offset range of the 400 \(\times\) 400 mm column is 1-8 cm from the edge, and the amplitude carried by the frequency gradually decreases with the increase in the distance from the edge. The frequency amplitude of 4.515 kHz gradually increases with the distance from the edge, and finally, the predominant frequency tends to be stable. Table 5 is the detection data of the 1000 \(\times\) 1000 mm column. The frequency change trend is shown in Figure 10.  
When the 1000 \(\times\) 1000 mm column is impacted at each interval of 1 cm from the edge mutation range, the predominant analytical frequency of the signal at the distance of 24-27 cm from the edge is 1.709 kHz, the predominant analytical frequency of the signal at the distance of 28-31 cm from the edge is 1.831 kHz. The mutation point is 28 cm from the edge. In this range, the amplitude carried by the low-frequency 1.709 kHz gradually \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Distance (cm)** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** \\ \hline Frequency (kHz) & 4.027 & 4.027 & 4.027 & 4.027 & 4.027 & 4.515 & 4.515 \\ \hline Amplitude (10\({}^{-6}\) m) & 0.420 & 0.397 & 0.374 & 0.352 & 0.328 & 0.311 & 0.318 & 0.326 \\ \hline \end{tabular}
\end{table} 
Table 4: The edge collects signal analysis results from every 1 cm (400 \(\times\) 400 mm). Figure 9: The edge acquires a spectrum every 1 cm: (**a**) spectrogram; (**b**) frequency change diagram of each point. decreases from 0.145 \(\times\) 10\({}^{-6}\) m to 0.135 \(\times\) 10\({}^{-6}\) m, and the amplitude carried by frequency 1.831 kHz gradually increases from 0.132 \(\times\) 10\({}^{-6}\) m to 0.136 \(\times\) 10\({}^{-6}\) m. It can be seen that frequency 1.709 kHz offset range of the 1000 \(\times\) 1000 mm column is 1-27 cm from the edge, and the amplitude carried by frequency gradually decreases with the increase in the distance from the edge. The amplitude carried by frequency 1.831 kHz gradually increases with the distance from the edge, and finally, the predominant frequency tends to be stable. Figure 11 shows the edge influence range of two different sizes of concrete columns. According to the simulation of the above three different section sizes of concrete columns, the influence range of the edge region can be judged. When the striking point is located within the scope of the edge influence distance, the predominant frequency of the receiving point signal produces a low-frequency offset phenomenon within this distance, which will cause errors in the actual test. The frequency mutation occurs at a particular position as the distance between the striking point and the edge moves further away. Then, the predominant frequency tends to be stable.