Non-destructive methods of assessing concrete and stone structure stability include using ground penetrating radar (GPR) [9; 10]. Another tool for determining the strength of concrete is the Schmidt rebound hammer, which is a surface hardness meter [11; 12; 13]. Knowing the relationship between the compressive strength of concrete and the rebound of the hammer, it is possible to estimate the strength parameter of concrete. The authors in the work [14] point out that [PERSON]'s jackhammer cannot accurately and directly fail to estimate the strength of concrete. The study [15] suggests using the SHM-X crackmeter and the classical geodetic method. The paper [16] demonstrates the use of LiDAR and the optimal dataset method to improve the crack-finding result. The important point is that with the help of non-destructive testing tools, only periodic monitoring can be carried out, while the cost of services is quite high since only specially trained people can work with them [17; 18; 19]. So, the issue of continuously monitoring and controlling buildings' technical conditions for the growth of cracks in monolithic concrete and reinforced concrete structures remains unresolved. Developing effective tools for early diagnosis of distributed and significant objects is very important. To monitor the technical condition of buildings and structures, there are successfully used tensometric, acoustic piezoelectric transducers, molecular-electronic, and fiber-optic strain gauges [20]. Among them, the most widespread are electrical sensors: strain gauges in thin rectangular foil strips with labyrinth wiring diagrams. The disadvantages of strain gauges are their limited length (up to 800 m), many cables, and the high cost of one control point. A scientific analysis of works that propose the use of optical fiber as a sensor and various options for monitoring the technical condition of reinforced concrete structures has been carried out. A popular solution is using FOS based on Bragg gratings [21; 22; 23]. The paper [24] presents a method for measuring the stress-strain state and total deformation of tensile stress concentration zones during concrete shrinkage using optical fibers and Bragg gratings. Some studies deal with developing systems for probing the slippage of reinforcing bars and joints in concrete structures based on Bragg gratings [25]. In study [26], fiber strain gauges with Bragg grating were proposed to detect damaged areas in bridge  
Figure 1: Cracks in the foundation. structures. There are systems for predicting normal deformations in pre-stressed concrete structures. The method uses Bragg gratings, a simplified analytical model of a concrete structure, and neural networks [27]. The use of Bragg gratings, in addition to their positive aspects, carries a sufficient complexity of the FOS design and a high cost. There are FOS based on the principle of operation of the Mach-Zehnder interferometer [28; 29; 30], which are designed to search for ultrasonic stress waves. The sensitivity of such sensors is highly dependent on the length of the optical fiber, and there is also a high noise level. Fabry-Perot interferometers are also used to assess the condition of concrete structures [31; 32]. In terms of the FOS application based on the operation of the Fabry-Perot interferometer, there is a crosstalk for eliminating which several basic methods are combined at once. In study [33], a hybrid system of a quasi-distributed FOS is described, which operates on the principle of a Fabry-Perot interferometer and Bragg gratings. Another method uses the Rayleigh scattering principle in a distributed FOS system [34; 35]. This method allows for obtaining data with a rather high spatial resolution, but it has limitations in the form of a measurement distance of up to 100 m. There are also systems using the Brillouin scattering principle [36; 37; 38]. There are studies showing comparisons between traditional methods and methods using FOS.