Assessment and visualization of performance indicators of reinforced concrete beams by distributed optical fibre sensing

Abstract

The implementation of structural health monitoring systems in civil engineering structures already in the construction phase could contribute to safer and more resilient infrastructure. Due to their lightweight, small size and high resistance to the environment, distributed optical fibre sensors stand out as a very promising technology for damage detection and quantification in reinforced concrete structures. In this article, the suitability of embedding robust distributed optical fibre sensors featuring a protective sheath to accurately assess the performance indicators, in terms of vertical deflection and crack width, of three reinforced concrete beams subjected to four-point bending is investigated. The results revealed that a certain strain attenuation occurs in embedded robust distributed optical fibre sensors compared to commonly used thin polyimide-coated distributed optical fibre sensors bonded to steel reinforcement bars. However, the presence of the protective sheath prevented the appearance of strain reading anomalies which has been a frequently reported issue. Performance wise, the robust distributed optical fibre sensors were able to provide a good estimate of the beam deflections with errors of between 12.3% and 6.5%. Similarly, crack widths computed based on distributed optical fibre sensor strain measurements differed by as little as ±20 µm with results from digital image correlation, provided individual cracks could be successfully detected in the strain profiles. Finally, a post-processing procedure is presented to generate intuitive contour plots that can help delivering critical information about the element’s structural condition in a clear and straightforward manner.

Long-Term Performance of Distributed Optical Fiber Sensors Embedded in Reinforced Concrete Beams under Sustained Deflection and Cyclic Loading

“…In a previous study by the authors [ 25 ], it was shown that when using robust fiber optic sensors embedded in concrete, most cracks could be clearly identified in the strain profiles as regions of strain localization and that the integration of the strain curve, within a neighboring region of the crack, provided a good approximation of the individual crack width without the need of additional analytical models. In the same study, it was demonstrated that when bending is dominant, performing a double integration of the curvature distribution, calculated from the strain distribution at two different heights of the beam, provides an accurate estimation of the deflections, given the right boundary conditions are applied.…”

A Review of Recent Distributed Optical Fiber Sensors Applications for Civil Engineering Structural Health Monitoring

“…A good agreement (±20 μm) was generally observed between DOFS and DIC crack widths monitoring, as can be seen in Figure 14. Berrocal et al [60] also investigated the suitability of embedded robust OFDR DOFS (featuring a protective external rugged polyamide coating) to accurately assess the per- This range is understandable considering the different depths at which the transversal cracks were measured and their probable lack of perpendicularity compared to the beams' axis. An additional takeaway was the need for a certain amount of strain noise-removing data post-processing in order to determine the crack position.…”

“…Berrocal et al [60] also investigated the suitability of embedded robust OFDR DOFS (featuring a protective external rugged polyamide coating) to accurately assess the performance requirements, in terms of vertical deflection and crack width, of three 20 × 25 × 300 cm RC beams subjected to four-point bending. The strain measurements performed by means of the thicker fiber were additionally integrated with the ones extracted from thin polyamide-cladded ones and from an external DIC system.…”

“…A good agreement (±20 μm) was generally observed between DOFS and DIC crack widths monitoring, as can be seen in Figure 14. Berrocal et al [60] also investigated the suitability of embedded robust OFDR DOFS (featuring a protective external rugged polyamide coating) to accurately assess the performance requirements, in terms of vertical deflection and crack width, of three 20 × 25 × Figure 14. Comparison between the crack width measured by the DIC and calculated from the DOFS measurements [59].…”

“…The robust DOFS were installed longitud along the rebars (Figure 15f) either supported along a longitudinal rebar, bridgin stirrups or resting on the formwork using electric tape to fix them in place (Figure 1 (f) Figure 15. Installation of the DOFS: (a) installation of robust DOFS cable in a reinforcement bar by inserting it into a previously milled groove; (b) comparison of thin and robust DOFS; (c) installation of thin DOFS on the surface of a rein forcement bar by bonding it with cyanoacrylate adhesive and protecting it with silicone; (d) installation of robust DOFS on the surface of a reinforcement bar by mechanically anchoring the cable to the reinforcement with electric tape; (e) multi layer configuration of embedded DOFS in the beam specimens and (f) loading setup and DOFS installation configuration for the RC beam specimens (adapted from [60]). (e) multi-layer configuration of embedded DOFS in the beam specimens and (f) loading setup and DOFS installation configuration for the RC beam specimens (adapted from [60]).…”