###### Abstract  
Reliable assessment and prediction of the technical condition of reinforced concrete structures require accurate data of the stress-strain state of the structure at all stages of loading. The most appropriate technique to obtain such information is digital image correlation. Digital image correlation is a class of contactless methods which includes the following stages: obtaining an image from a studied physical object, saving it in digital form, and further analysis in order to obtain the necessary information about the stress-strain state of the structure. In this research, a detailed analysis of theoretical and experimental findings of digital image correlations was conducted. In the article, the main areas of scientific interest and computational approaches in digital image correlation issues were identified. Moreover, comparative analysis of alternative non-contact techniques, which also could be used for diagnostics of RC structures' stress-strain state was conducted. The novelty of the study consists of a thorough comparative analysis with the indication of specific features of digital image correlation, which determine its wide application among the other similar methods. On the basis of the conducted literature review, it can be seen that the digital image correlation technique has gone through multi-stage evolution and transformation. Among the most widely studied issues are: image recognition and matching procedures, calibration methods and development of analytical concepts. The digital image correlation technique enables us to study cracking and fracture processes in structural elements, obtaining the full field of deformations and stresses. Further development of image processing methods would provide more precise measuring of stress-strain parameters and reliable assessment of structural behavior. digital image correlation; structure performance; stress-strain state; cracking; monitoring; technical assessment +
Footnote †: _Scienced Reviews of Applied and Applied Sciences_
the physical and mechanical characteristics of materials and the actual parameters of work under loading [6; 7; 8; 9]. In order to obtain these data, a significant number of experimental studies under both laboratory and field conditions should be conducted, which is often economically impractical [1]. In the theoretical modeling of the structure, using both numerical methods and automated software, it is necessary to take into account the individual contribution of each of the parameters of the structural reaction. These results are valuable in determining the necessary strengthening of structural elements and make assumptions on the possibility of its further operation. The leading trend in engineering is the evolution from the planned monitoring of the technical condition toward the prediction of its changes on the basis of parameters identified by non-destructive studies of real structures [10]. It is obvious that in order to achieve this goal it is necessary to operate with data of the structure stress-strain state at all stages of loading with high accuracy, which is technically impossible when using classical methods of experimental research. Accordingly, techniques with the use of digital image correlation have recently become widespread. Digital image correlation (DIC) is a class of contactless methods which includes the following stages: obtaining an image from studied physical object, saving it in digital form, and further analysis in order to obtain the necessary information about the stress-strain state of the structure [11]. Data analysis consists of comparison of the surface reference image before the application of the load (reference image-RI) with the images corresponding to the different stages of the deformation process (deformed images-DI) [12; 13].