**4. Experimental Analysis**

The span of common small and medium bridges is 24 m. According to the actual bridge, an aluminum box-type simply supported girder bridge was designed by the scale of 1:7.5. The modulus of elasticity was set to 69 GPa, the Poisson's ratio was 0.33, the density was 2700 kg/m3, the dead weight was 13.07 kg, and the first-order natural vibration frequency was 16.23 Hz. Thirty-two long-gauge fiber Bragg grating strain sensors were pasted along the span of the upper roof of the beam to measure the compressive strain (taking the absolute strain value). Subsequently, the beam was divided into 32 longgauge elements of 10 cm each. A temperature compensation sensor of the same type was connected in series. After the bonding was completed, the wavelength of the sensor was calibrated, and the wavelength of 33 strain sensors with long gauge at the same time was recorded as the initial value. Figure 4 shows the vehicle–bridge experimental model and sensor layout. The self-weight of the mobile trolley was 8 kg, and its mass could be varied by adding weight, as shown in Figure 5. Table 1 lists the damage condition settings. Figure 6 shows the experimental operation [33–35].

**Figure 4.** Vehicle–bridge experimental model and sensor layout diagram.

**Figure 5.** Mobile trolley.

**Table 1.** Damage condition table.


Note: The damage degree is the percentage of damage in the entire long-gauge element. Damage width refers to the length of failure along the bridge direction at the bottom part of the box girder, which is similar to the crack. The damage location is set in the 26th or 6th long-gauge element of the lower bottom plate of the box girder. According to the damage length of the bottom plate of the box girder and the degree of damage of the web, the damage degree is comprehensively set according to the average stiffness reduction method, in which the working conditions D1 and D2 are the same damage width of the bottom plate of the box girder, and the damage of the D2 web is larger, and the overall stiffness is small. The damage is stronger, so the damage degree of D2 is greater than that of D1. D3 and D4, D5 and D6 are also set in the same way.

**Figure 6.** Sensor installation and experimental operation.
