Distributed Fiber Optic Shape Sensing of Concrete Structures

Distributed fibre optical sensing (DFOS) is increasingly used in civil engineering research. For reinforced concrete structures, almost continuous information concerning the deformations of embedded reinforcing bars can be obtained. This information enables the validation of basic and conventional assumptions in the design and modelling of reinforced concrete, particularly regarding the interaction of concrete and reinforcing bars. However, this relatively new technology conceals some difficulties, which may lead to erroneous interpretations. This paper (i) discusses the selection of sensing fibres for reinforced concrete instrumentation, accounting for strain gradients and local anomalies caused by stress concentrations due to the reinforcing bar ribs; (ii) describes suitable methods for sensor installation, strain acquisition and post-processing of the data, as well as determining and validating structurally relevant entities; and (iii) presents the results obtained by applying DFOS with these methods in a variety of experiments. The analysed experiments comprise a reinforced concrete tie, a pull-out test under cyclic load, and a flexural member in which the following mechanical relevant quantities are assessed: the initial strain state in reinforcing bars, normal and bond shear stresses, deflections as well as forces. These applications confirm the benefit of DFOS to better understand the bond behaviour, but also demonstrate that its application is intricate and the results may lead to erroneous conclusions unless evaluated meticulously.

Section: Introductionmentioning

confidence: 99%

Application of Distributed Fibre Optical Sensing in Reinforced Concrete Elements Subjected to Monotonic and Cyclic Loading

Lemcherreq

Galkovski

Mata‐Falcón

et al. 2022

“…The acquired data with c-OFDR is of unprecedented quality, thanks to the strain measurement's low invasiveness and quasi-continuity. Monsberger and Lienhart showed the possibility to assess the curvature, bending moment and deflection distribution in grouted soil anchors monitored longitudinally with at least two fibres [3] and introduced a concept for distributed fibre optic shape sensing in concrete structures [16]. Instrumenting steel reinforcing bars with quasi-continuous fibre optical strain measurements also allows getting a deep insight into the crack behaviour of reinforced concrete members without the necessity of knowing the crack locations in advance [17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Fundamental Studies on the Use of Distributed Fibre Optical Sensing on Concrete and Reinforcing Bars

Galkovski

Lemcherreq

Mata‐Falcón

et al. 2021

Distributed fibre optical sensing (DFOS) allows for quasi-continuous strain measurement in a broad range of gauge lengths and measurement frequencies. In particular, Rayleigh backscatter-based coherent optical frequency domain reflectometry has recently registered a significant application increase in structural concrete research and monitoring thanks to its numerous merits, such as high resolution and low invasiveness. However, it is not a plug-and-play technique. The quality of the acquired data depends highly on the choice of the fibre optical sensor and the methods of instrumentation and post-processing. Furthermore, its unprecedented resolution and sensitivity allow capturing local effects not well documented so far. This paper analyses the suitability of DFOS based on Rayleigh backscatter for reliably measuring strains and discusses the origin and structural relevance of local variations in the results. A series of experimental investigations are presented, comprising tensile tests on bare reinforcing bars and concrete compression tests. A critical analysis of the results leads to a best practice for applying DFOS to reinforcing bars and concrete, which establishes a basis for reliable, accurate measurements in structural concrete applications with bonded reinforcement.

“…The list of its varieties is constantly expanding [ 1 , 2 ]. Mechanical phenomena, both during concrete hardening and during operation [ 3 ] and ageing [ 4 ] of particularly critical concrete structures, such as hydraulic structures, are important data that require analysis and study. This is the scientific direction of structural health monitoring (SHM) [ 5 ], which is actively developing due to the emergence of new materials [ 6 ].…”

Section: Introductionmentioning

confidence: 99%

“…This allows the critical defects in the structure to be found in time, thus preventing disasters. The most used instruments in SHM are point-wise [ 3 ] and distributed fibre-optic sensors (DOFS) [ 7 , 8 , 9 ]. DOFS are mostly based on various principles of optical reflectometry.…”

Section: Introductionmentioning

confidence: 99%

Improving Prediction Accuracy and Extraction Precision of Frequency Shift from Low-SNR Brillouin Gain Spectra in Distributed Structural Health Monitoring

Nordin

Abdullah

Zan

et al. 2022

In this paper, we studied the possibility of increasing the Brillouin frequency shift (BFS) detection accuracy in distributed fibre-optic sensors by the separate and joint use of different algorithms for finding the spectral maximum: Lorentzian curve fitting (LCF, including the Levenberg–Marquardt (LM) method), the backward correlation technique (BWC) and a machine learning algorithm, the generalized linear model (GLM). The study was carried out on real spectra subjected to the subsequent addition of extreme digital noise. The precision and accuracy of the LM and BWC methods were studied by varying the signal-to-noise ratios (SNRs) and by incorporating the GLM method into the processing steps. It was found that the use of methods in sequence gives a gain in the accuracy of determining the sensor temperature from tenths to several degrees Celsius (or MHz in BFS scale), which is manifested for signal-to-noise ratios within 0 to 20 dB. We have found out that the double processing (BWC + GLM) is more effective for positive SNR values (in dB): it gives a gain in BFS measurement precision near 0.4 °C (428 kHz or 9.3 με); for BWC + GLM, the difference of precisions between single and double processing for SNRs below 2.6 dB is about 1.5 °C (1.6 MHz or 35 με). In this case, double processing is more effective for all SNRs. The described technique’s potential application in structural health monitoring (SHM) of concrete objects and different areas in metrology and sensing were also discussed.