PSI - Issue 64

Bartosz Piątek et al. / Procedia Structural Integrity 64 (2024) 1581–1588 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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appropriate solution for diagnostic purposes. In this test three types of sensors were compared: bare optic fibers (G), stiff EpsilonRebars (ER) and flexible EpsilonSensors (ES). It was important to answer the question about the possible influence of the axial stiffness of the sensors on the crack-induced strain profiles. A comparison of strain profiles obtained using ER and ES sensors is presented in Fig. 5. Flexible sensors (ES) exhibited larger amplitudes as compared to strain distributions based on stiff sensors results (ER), revealing a higher sensitivity of these measurement tools and their better potential for detecting concrete cracks. Similarly, bare optical fibers (G) were very sensitive but due to the high susceptibility to damage, their effective installation can only be performed under laboratory conditions. Therefore, it was decided to select flexible sensors ES for further research (damage detection).

Fig. 5. Comparison of strain profiles obtained using ES and ES sensors in beam QPT1.

3.2. Damage detection

The main aim of the QPT test was to check if it is possible to find simulated damages using the DFOS system. Figure 6 presents an exemplary comparison of strains recorded in both QPT1 and QPT2 beams by ES sensors located inside the cable ducts (see location of void in Fig. 2). The test revealed, that it was possible to identify the location of the damage in the form of a void inside the cable duct. In the beam QPT1, two strain peaks are visible in the middle of the span, demonstrating the cracking of the beam, which was also recorded in the grout. However, in the location of the void in beam QPT2, a clear flattening of the strain curve of the gauge is visible due to the lack of sensor adhesion.

Fig. 6. Comparison of strain profiles obtained using ER sensors located inside cable ducts in beams QPT1 and QPT2.

Full-scale test results (PT beams) 3.3. Concrete cracking

Based on the DFOS measurements, it was possible to detect cracks forming in the lower section of the beams under bending. Based on the measured strain profiles, an analysis was conducted to estimate the width of these new cracks.