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

Abstract

This paper explores the performance of distributed optical fiber sensors based on Rayleigh backscattering for the monitoring of strains in reinforced concrete elements subjected to different types of long-term external loading. In particular, the reliability and accuracy of robust fiber optic cables with an inner steel tube and an external protective polymeric cladding were investigated through a series of laboratory experiments involving large-scale reinforced concrete beams subjected to either sustained deflection or cyclic loading for 96 days. The unmatched spatial resolution of the strain measurements provided by the sensors allows for a level of detail that leads to new insights in the understanding of the structural behavior of reinforced concrete specimens. Moreover, the accuracy and stability of the sensors enabled the monitoring of subtle strain variations, both in the short-term due to changes of the external load and in the long-term due to time-dependent effects such as creep. Moreover, a comparison with Digital Image Correlation measurements revealed that the strain measurements and the calculation of deflection and crack widths derived thereof remain accurate over time. Therefore, the study concluded that this type of fiber optic has great potential to be used in real long-term monitoring applications in reinforced concrete structures.

Monitoring of new and existing stainless-steel reinforced concrete structures by clad distributed optical fibre sensing

“…24 and further developed by the authors of refs. 25 and 26 is used in this section to measure crack widths from the different strain measurements. Therefore, the crack width of individual bending cracks can be calculated with an accuracy of ± 20 µm based on the strain measured by the DOFS at the tensile reinforcement according to equation (1)where ε DOFS (x) is the measured strain (at the bottom reinforcement), trueε^(x) is the strain varying linearly between cracks, ρ=As/Ac,ef and α=Es/Ec are the reinforcement ratio and the modular ratio, respectively, and lt,i− and lt,i+ are the ends of transmission length along which slips occurs, assumed as the valleys in the strain profile to the left and right sides of the i-th crack, w cr,i .…”

“…Brault and Hoult 23 had previously shown that multiple cracks as well as deflections could be also accurately measured using DOFS longitudinally bonded to the surface of RC beams. Further experimental work by Berrocal and Fernandez [24][25][26] revealed that by using strain measurements from robust DOFS, a good estimation of the crack width of multiple individual bending cracks and deflections in RC beams can be achieved, without the inclusion of strain transfer models between the fibre core and the substrate element, both for short and long-term monitoring.…”

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

“…The dynamic loads and subsequent loading to failure did not cause an impairment in the DFOS performance [29]. Fernandez et al (2021) assessed the long-term performance of robust fibre optical cables with a steel tube embedded in concrete and subjected to different loading conditions. By comparing integrated values (i.e., deflection and crack width) to DIC measurements, they concluded that the DFOS measurement remained stable over time [30].…”

“…Fernandez et al (2021) assessed the long-term performance of robust fibre optical cables with a steel tube embedded in concrete and subjected to different loading conditions. By comparing integrated values (i.e., deflection and crack width) to DIC measurements, they concluded that the DFOS measurement remained stable over time [30]. The deterioration of bond properties with increasing load cycles was investigated in the first application of DFOS with high cyclic loading [16].…”

Effective reinforcement ratio of RC beams: Validation of modelling assumptions with high‐resolution strain data

“…This study uses advanced measurement technologies to investigate these unknowns: distributed fibre optical sensing (DFOS) and digital image correlation (DIC) have emerged as suitable tools to investigate the local structural behaviour of RC elements. [16][17][18][19][20] Three approaches to estimate tension stiffening-related properties directly from DFOS and DIC measurements are presented and applied to a highly reinforced concrete beam tested in four-point bending. Selected models for the effective reinforcement ratio and the cracking behaviour for pure bending are validated against the experimental data.…”