## 4 Analysis of Bridge Deformation Characteristics
### Dynamic Deformation Characteristics of the Fenghuangshan Road Bridge Based on GB-RAR Technology
#### 4.1.2 Dynamic Deformation Characteristics of the Bridge with a 100 Hz Sampling Frequency  
Under the 100 Hz sampling frequency condition, the IBIS micro-deformation monitoring system was utilized to monitor the Fenghuangshan Road Bridge, and the monitoring time was 1230.38 s. Part of the monitoring data was extracted to draw the deflection deformation time series curve of the bridge at different positions (Figure 17). Figure 16: Overall deformation of the bridge at different times with a 50 Hz sampling frequency. Figure 17: The 100 Hz sampling frequency monitoring diagram. Figure 15: Overall deformation of the bridge at different times with a 50 Hz sampling frequency. It was observed that the different positions of the bridge fluctuate around a certain horizontal line, which is consistent with the motion characteristics of nonlinear elastic deformation. It can be observed from Figure 18 that point C at the southern end of the bridge deformed \(-1.2\) mm at 155.47 s and continued to move along the gravity direction, and that it deformed \(-47.2\) mm at 156.05 s and deformed in an inverted \"V\" shape at 61.6 s to 61.8 s; furthermore, the maximum deformation value of the antigravity direction was 26.6 mm. As can be observed from Figure 19, during the period from 155.70 s to 156.00 s, the minimum deformation value of bridge point E is 10.2 mm, the maximum deformation value is 23.2 mm, the amplitude is 13 mm, the vibration period is 0.12 s, and the vibration frequency is 8.33 Hz. Additionally, deformation of this point is \(-16.6\) mm at 383.18 s and \(-2.43\) mm at 383.26 s. The vibration period is 0.16 s, and the vibration frequency is 6.25 Hz. It can be observed from Figure 20 that under the action of vehicle dynamic load, different bridge positions exhibit different deformation characteristics, with the largest deformation at point C, the second at point E, and the smallest deformation at point A. In Figure 20a, point C is deformed by \(-26.0\) mm at 274.60 s and returns to the peak position at 274.82 s. The vibration period is 0.22 s, and the vibration frequency is 4.54 Hz. Point E  
Figure 19: The 100 Hz sampling frequency: second monitoring results. (**a**) 155.7–156.0 s; (**b**) 383.1–383.4 s.  
Figure 18: The 100 Hz sampling frequency: first monitoring results. (**a**) 155.4–156.1 s; (**b**) 61.5–61.9 s.  
of the bridge attains a trough at 274.76 s, deformation is \(-5.5\) mm, and a peak is attained after 0.12 s. The deformation is 3.5 mm, the vibration period is 0.24 s, and the vibration frequency is 4.17 Hz. In Figure 20b, the deformation characteristics of point A are similar to those of point E. Point C fluctuates exceedingly, and the deformation is 27.1 mm at 381.99 s.  
To comprehensively describe the differences in the motion characteristics of different bridge positions, this study extracts the bridge deformation data at 1000s\(-\)1075s during the monitoring period, and it creates a comparison chart that depicts the dynamic deformation trend of different bridge positions, defining the direction of gravity as the negative direction and vice versa. As can be observed from Figure 21, during this period, the deflection deformation trend at different bridge positions presents an inverted \"V\" shape, first increasing and then decreasing. At points A, B, F, and G, the maximum deformation values are 7.54 mm, 6.34 mm, 9.63 mm, and 22.12 mm, respectively, and the maximum positive deflection at point D is 12.78 mm. The minimum negative deflection is \(-\)16.24 mm. Judging from the maximum forward deflection deformation, the overall deformation of the bridge exhibits a sinusoidal curve. Because, during the green light, the northern bridge section is affected by the dynamic load of vehicles, rebound deformation subsequently occurs under the action of self-rigidity. The greater the impact of the dynamic load of the vehicles, the stronger the rebound deformation. Meanwhile, the rebound deformation of the bridge across the middle and the northern bridge sections is the strongest.