# Nondestructive Monitoring Techniques for Crack Detection and Localization in RC Elements
## 11 Conclusions  
The implementation of integrated SHM schemes of nondestructive testing techniques is presented in this paper for a reinforced concrete beam tested in laboratory through a four-points bending arrangement. The beam is subjected to loading stages to induce characteristic concrete cracking and steel reinforcements yielding. All of these phases have been identified in a global behavior curve in terms of force-displacement measurements.  
The strain measures of the embedded fiber optic system have been compared to the acoustic emission sensors' outcomes. Furthermore, visual observation of the actual cracks pattern has been also considered in parallel with DIC analysis in the central region of the beam specimen.  
The recorded AE activity resulted in good agreement with FOS strain measurements. Furthermore, the results of the AE-FOS integrated SHM system are confirmed by the actual cracks pattern. Focusing on the pure bending moment region of the specimen, the strain field computed by DIC also resulted in good agreement with the FOS tensile strains at the bottom side of the specimen.  
A numerical model has also been prepared to investigate the mechanical behavior of the beam up to collapse. The analysis has been focused on both the global behavior in terms of force-displacement response, and also the local characterization of cracks. A satisfactory match between the numerical outcomes and the monitoring data has been observed.  
Figure 16: (**a**) Force–displacement response up to collapse, (**b**) development of cracks at step #8.  
Therefore, the integrated use of different nondestructive testing techniques as proposed in this paper is a reasonable and reliable SHM strategy for damage detection and localization in RC elements. This study confirms how the application of different nondestructive testing techniques can be useful for specific civil engineering applications, e.g., for large-sized structural elements where visual inspection is not always possible and accurate. Thus, the simultaneous use of nondestructive testing techniques such as acoustic emission, embedded fiber optic sensors, and digital image correlation, possibly aided by visual inspection, seems to be a step toward the realization of a reliable real-time structural alert system.  
Conceptualization, M.D., G.N., G.L., G.P.C.; investigation and data curation, M.D., G.N.; writing--review and editing, M.D., G.N., G.L.; supervision and project administration, G.P.C. All authors have read and agreed to the published version of the manuscript.  
The research is partially supported by the European Research Council under the Grant Agreement n\({}^{\circ}\) ERC_IDEalreFCSUE_637842 of the project IDEAL RESCUE-Integrated Design and control of Sustainable Communities during Emergencies.  
[PERSON] assisted the laboratory analyses in partial fulfillment for the requirements of the Bachelor's Degree in Civil Engineering at Politecnico di Torino, under the guidance of the Authors. His contribution is gratefully acknowledged. The technical support of SMARTEC (CH) and MastrLab at Politecnico di Torino-DISEG is gratefully acknowledged.  
The authors declare no conflict of interest.