# Research on Damage Localization of Steel Truss-Concrete Composite Beam Based on Digital Orthoimage
## 6 Conclusions  
Using digital image processing techniques, an image matrix similarity damage identification method for bridge structures is proposed based on the ability of images to describe the holographic deformation of structures. The test results show that the method can accurately identify the singular signal of local stiffness degradation caused by structural damage from the overall structural deformation and achieve the localization of damage. This solves the difficulty of damage identification due to incomplete test data and provides a new idea for beam damage identification. The research in this paper has engineering application prospects for small and medium-span bridges and for fast, economic, and efficient long-term health monitoring. The main conclusions of this paper are as follows.  
(1) A digital orthophoto-based image matrix similarity damage identification method is proposed. Numerical simulation studies show that the damage will break the structural system deformation coordination, the abnormal distribution of pixels at the damage site will manifest odd signals in the matrix similarity test before and after the damage, the signal characteristics are shown as similarity curve discontinuity, and the discontinuity location is consistent with the damage site.  
(2) A damage loading test of steel truss-concrete composite beam has been conducted, and the original test beam image is corrected by perspective transformation to obtain an equivalent digital orthophoto. Further, the holographic morphology of the test beams extracted by the SIFT feature extraction algorithm is verified, and the results show that the extracted morphology of the test beams is consistent with the real morphology of the structure.  
(3) The lower edge curve of the experimental beam is affected by noise with regular oscillation, and the noise-containing curve is processed by the wavelet denoising function to obtain a continuous smooth lower edge curve of the structure. The validation results show that the maximum error of the noise-reduced curve is 3.42%.  
(4) The image matrices of the structure before and after the damage are obtained from the coordinates of the lower edge curve. The similarity envelopes for each damage condition were derived by calculating the similarity of the image matrices under single damage condition and multiple damage conditions. The peak of the envelope is consistent  
Figure 44: Similarity envelopes for all damage conditions.  
with the position of the damaged rod, which verifies the accuracy of the damage position identification in practical applications.  
Conceptualization, R.L. and X.C.; methodology, formal analysis, and investigation, R.L., X.L. and J.M.; writing--original draft preparation, R.L.; writing--review and editing, R.L. and X.C.; visualization, R.L.; supervision, Z.Z. and X.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant No. 51778094).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.