Performance of Rayleigh-Based Distributed Optical Fiber Sensors Bonded to Reinforcing Bars in Bending

Abstract

Distributed Optical Fiber Sensors (DOFSs), thanks to their multiple sensing points, are ideal tools for the detection of deformations and cracking in reinforced concrete (RC) structures, crucial as a means to ensure the safety of infrastructures. Yet, beyond a certain point of most DOFS-monitored experimental tests, researchers have come across unrealistic readings of strain which prevent the extraction of further reliable data. The present paper outlines the results obtained through an experimental test aimed at inducing such anomalies to isolate and identify the physical cause of their origin. The understanding of such a phenomenon would enable DOFS to become a truly performant strain sensing technique. The test consists of gradually bending seven steel reinforcement bars with a bonded DOFS under different conditions such as different load types, bonding adhesives, bar sections and more. The results show the bonding adhesives having an influence on the DOFS performance but not on the rise of anomalies while the reasons triggering the latter are narrowed down from six to two, reaching a strain threshold and a change in structure’s deformative behavior. Further planned research will allow identification of the cause behind the rise of strain-reading anomalies.

Composite Anchors for Slope Stabilisation: Monitoring of their In-Situ Behaviour with Optical Fibre

“…The spikes that are observed in the strain curves at larger loads are not real, likely due to the correlation algorithm used to track the Rayleigh shift in the OFDR interrogator, which can fail when a very large spatial strain gradient occurs. Interestingly, similar spikes have been observed in other applications [36], yet were ascribed to physically-induced anomalies rather than to a limitation of the measurement technique. Unfortunately, due to the squeezing effect, the strain gradient reaches high values early on during the test, although the strain in the middle of the bar is still within the measurable range.…”

Crack monitoring in reinforced concrete beams by distributed optical fiber sensors

“…As a result, the suitability of optical fiber systems in SHM has already been tested for various experiments in the laboratory, see e.g. (Bado, Casas, & Barrias, 2018;Bao, Meng, Chen, Chen, & Khayat, 2015;Sienko, Bednarski, & Howiacki, 2019;Zeng et al, 2002), as well as field applications, see e.g. (Barrias, Rodriguez, Casas, & Villalba, 2018;Brault, Hoult, Greenough, & Trudeau, 2019;Gli si c, Posenato, & Inaudi, 2007;Matta, Bastianini, Galati, Casadei, & Nanni, 2008).…”

Distributed Optical Fiber Sensing Bonding Techniques Performance for Embedment inside Reinforced Concrete Structures

“…In most cases the DOFS are attached directly to the surface of the reinforcement-bars (rebars) before the latter are embedded inside concrete. Multiple studies [ 4 , 8 , 9 , 10 , 11 ] have demonstrated that the technique with which this bonding is achieved has a prominent role in the quality of the extracted data. Indeed, the highly sensitive nature of these hair-like fibers intrinsically exacerbates the probability of its malfunctioning and/or rupture during the concrete casting, maneuvering and testing phase.…”

“…The importance of this issue has only lately been recognized as all the produced publications date back to last decade [ 12 , 13 , 14 , 15 ]. Worthy of mention, are two extensive studies analyzing the influence of different bonding adhesives on the strain output of polyamide cladded DOFS attached to bare rebars [ 11 ] and concrete surfaces [ 16 ]. Yet, no definitive comparative study has been developed for the case of DOFS bonded to rebars when embedded inside RC structures.…”

“…Unfortunately, as will be visible later on, this is a very common and undesirable occurrence plaguing almost every single DOFS monitored campaign. Bado et al [ 11 , 17 ] attempted to study these SRAs. According to them a strain peak at a general DOFS coordinate x k is usually considered as an abnormal reading if it presents a large difference with previous reading at coordinate x k− 1 .…”