## 3 Image Feature-Based Extraction of Damage Indicators
### Residual Bearing Capacity Extraction Algorithm
#### 3.1.2 Residual Bearing Capacity Extraction
Considering only the case of self-weight, the stress magnitude at the height, h, of the abutment is: \[\sigma=\rho g(H-h)+\rho g*0.5L,\] (4) where \(\rho\) denotes the density of reinforced concrete, \(g\) denotes the acceleration of gravity, \(H\) is the height of the bridge abutment, and \(L\) is the length of the bridge deck. Figure 4: Schematic diagram of relative damage area ratio. For this experimental bridge, \(L\) = 30 m, \(H\) = 3 m. To simplify the calculation, the abutment is divided into upper and lower parts, and as the stress ratio of the upper and lower parts is about 1.1, the weight ratio is 1.1. The calculation can obtain that the upper half of the weight value is 0.48, and the lower half of the weight value is 0.52. The penetration damage and damage to the missing areas are regarded as a complete penetration with a penetration through half of the thickness, so its weight ratio is 2. Therefore, the weights of the damage types of the bridge piers are obtained as shown in Table 1.  
For bridge decks, more factors need to be considered in the calculation of residual capacity due to the presence of girders. T-girder bridges consist of flanges, webs, and wet joints. The wet joints occupy a small area and are equivalent in strength to the flanges, so the deck can be equated to the flanges and the web. For the general case of munitions strikes, the web will not be completely destroyed and may occur in the upper part of the missing area, which has a small impact on its mechanics, so the web destruction can be ignored. Therefore, for T-girder bridges without prestressing technology, the main damaged structure from a munitions strike is the T-girder flange, so when dealing with it, according to the most unfavorable conditions, the craters will all damage the girders. Analyzed from the loading point of view, the simplified bridge deck is subjected to an evenly distributed load, and the middle bending moment of the bridge deck is the largest and the damage is more likely to cause collapse. In order to simplify the calculation, the bridge deck is divided into four blocks, the two blocks near the center are one part, and the two ends are the other part, so its bending moment ratio is 2; i.e., the weight ratio is 2. Calculations can obtain that the weight value of the middle part of the bridge deck is 0.67, and the value for the two ends of the bridge deck is 0.33. For the penetrating and missing damage, it is considered to be a complete penetration with penetration through half of the thickness, so its weight ratio is 2. Therefore, the obtained weight values for the bridge deck damage types are shown in Figure 2:0  
Fusing the residual bearing capacity characteristics of the abutments and bridge decks, the method of taking the maximum value is used to ensure the accuracy and uniqueness of the final result, so it can be obtained that the residual bearing capacity characteristics of the bridge are calculated as follows:  
Figure 2:1  
where \(RBC\) denotes the residual load rating after fusion, \(RBC_{p}\) denotes the residual load rating of the abutment, and \(RBC_{d}\) denotes the residual load rating of the deck. The use of image features for the load-bearing capacity template matching can quantify the residual load-bearing capacity index of the bridge in the case of no contact and no damage, avoiding the complex load-bearing capacity formula calculation; the algorithm