PSI - Issue 64

Luca Schenato et al. / Procedia Structural Integrity 64 (2024) 1636–1641 Luca Schenato / Structural Integrity Procedia 00 (2019) 000 – 000

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Given the SCA's capability to correlate traces, despite the conditions, it can be used to perform such a task if any of the preparatory traces are available. Figure 3 shows an example of this: the strain curve corresponds to the strain accumulated by cable 3 during the installation phase. The reference of this curve was taken in the lab during the cable's preparation. The measurement refers to the trace collected at the end of 2016 (i.e., the reference chosen for the curves of Fig. 2). Note that the average strain imparted during the installation is more than 3300  , a value that corresponds to 33 % of the nominal maximum strain tolerated by the cable. Moreover, the strain curve shows a large local spatial gradient, with variations of more than 500  within a few tens of centimeters, which is frozen within the fiber after the concrete cures. This high spatial variability testifies to the harshness of the condition that the fiber underwent during installation. This high variability testifies to the roughness of the installation. This represents a further useful feature enabled by the SCA method, which provides better insight into the application of DOFS to structure in challenging conditions. 4. Conclusions In this study, we have explored the Rayleigh fingerprint in fibers used under extreme conditions. By collecting measurements in fibers under challenging conditions, we have verified that the fingerprint is persistent despite the conditions, the time passed from the reference measurement, and the optical setup used to perform the measure. In particular, the fibers of this study were exposed to unremitting contraction or elongation of thousands of microstrain, with localized large spatial gradients, after a large strain, with high spatial variability, was imparted during the installation. In conclusion, we believe this study paves the way for long-term Rayleigh monitoring campaigns, even with changing interrogators or patch cords, as the reference measurement can be reliably kept over many years despite adverse events. Acknowledgments The authors acknowledge partial support from the European Union under the Italian National Recovery and Resilience Plan (NRRP) of NextGenerationEU, partnership on “ Telecommunications of the Future ” (PE0000001 - program “ RESTART' ” ) and MIUR (Project PRIN – 2022HFWMPC – “ Debris Phos ” ). Bersan, S., Bergamo, O., Palmieri, L., Schenato, L., Simonini, P., 2018. Distributed strain measurements in a CFA pile using high spatial resolution fibre optic sensors. Engineering Structures, 160, 554 – 565. Boiron, H., Pillon, J., Peter, E., Robin, T., Villedieu, T., Morana, A., Girard, S., Boukenter, A., Marin, E., Lefevre, H., 2020. Optical fiber strain and temperature coefficients determination based on Rayleigh-OFDR, Optical Fiber Sensors Conference 2020. Washington, DC, United States, paper T3.42. Cappelletti, M., Aitkulov, A., Orsuti, D., Schenato, L., Santagiustina, M., Hayashi, T., Galtarossa, A., Palmieri, L., 2023. Distributed fiber optic shape sensing with simultaneous interrogation of multiple fibers based on Rayleigh-signature domain multiplexing. Optics Letters, 48, 5907 5910. Cola, S., Schenato, L., Brezzi, L., Tchamaleu Pangop, F. C., Palmieri, L., Bisson, A., 2019. Composite anchors for slope stabilisation: Monitoring of their in-situ behaviour with optical fibre. Geosciences 9. Cola, S., Schenato, L., Simonini, P., Bersan, S., Tchamaleu Pangop, F. C., Michielin, E., 2019. On distributed strains in a CFA pile via DFOSs measurements and numerical analysis. 17th European Conference on Soil Mechanics and Geotechnical Engineering (ECSMGE-2019). Reykjavik, Island. Froggatt, M., Moore, J., 1998. High-Spatial-Resolution Distributed Strain Measurement in Optical Fiber with Rayleigh Scatter. Applied Optics, 37, 1735 – 1740. LUNA OBR 4600: Optical Backscatter Reflectometer. [(accessed on 28 March 2024)]. Available online: https://lunainc.com/product/obr-4600. Palmieri, L., Schenato, L., Santagiustina, M., Galtarossa, A., 2022. Rayleigh-based distributed optical fiber sensing, Sensors, 22, 6811. Veronese, R., Galtarossa, A., Palmieri, L., 2020. Distributed characterization of few-mode fibers based on optical frequency domain reflectometry. Journal of Lightwave Technology, 38(17), 4843 – 4849. References