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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first measurements. Unfortunately, as for the previous site, the monitoring campaign was interrupted for changes in the optical interrogator and patch cords. For example, Fig. 2 shows the last measurements performed in 2018, along with the more recent ones in June 2023, performed with a different optical setup and made possible with the aid of the SCA method. The reference traces were collected at this site at the end of 2016 after the abutment raft foundation was completed. For both cables examined here, the traces show evidence of similar trends, with common events between the older and the more recent measurement sessions (e.g., events labeled with  ,  and  ). The consistency of strain behavior among traces represents a further confirmation of the ability of the method to reveal the persistent Rayleigh fingerprint effectively.

Fig. 2. (a) Strain measured at cable 3 of the CFA pile in May 2017 and Jun. 2023, and (b) at cable 4 vs. depth below sea level (b.s.l.).

The method can also be employed to back-analyze traces collected in different moments without a common spatial reference. Indeed, very often, in the preparation phase, the sensing cables are tested in the lab with either a temporary or a permanent patchcord spliced at one end; this is done to cut the required length of cable from the reel, verify the absence of any anomalies in the Rayleigh intensity trace, check for anomalous Fresnel peak at the end of the cable. Then, the cables are integrated into the structure, e.g., the foundation pile or the anchor, and, if needed, spliced on the field. These preparatory traces shouldn’t be used as references , as they do not represent the rest condition of the structure. However, the information about the amount of strain induced during installation can provide useful information about the harshness of the integration procedure. Nonetheless, given that they are collected in the lab under different setups, they couldn’t normally be used for referencing any of the following measurements taken on the field.

Fig. 3. Strain accumulated during the installation phase within the foundation pile by cable 3 with respect to the laboratory preparation phase.