Crack detection and vertical deflection monitoring in concrete beams using plastic optical fibre sensors

Abstract

Plastic optical fibres have been employed to detect initial cracks, monitor post-crack vertical deflection and detect failure cracks in concrete beams subjected to flexural loading conditions. The intensity-based sensor system relies on monitoring the modulation of light intensity within the optical fibre as the sensor is loaded. The sensor design offers good signal stability and sensitivity to the monitored parameter and represents a cost-effective alternative to other more sophisticated health-monitoring systems currently used in civil engineering structures.Here, a series of three-and four-point bend tests was conducted on a range of structures. Initially, the optical fibres were attached to scale-model concrete samples (without reinforcement) to evaluate their ability to monitor beam deflection and detect cracks. Similar tests were subsequently conducted on life-size concrete beams containing reinforcing steel bars. The location and subsequent trajectory of cracks during the loading regime were marked and then compared to the sensor signal to assess the sensor's ability to monitor crack development.The results demonstrate the possibility of using optical fibres to detect hairline cracks and ultimate failure crack in civil engineering structures and highlight their ability to monitor crack propagation up to ultimate failure. In addition to detecting the initiation of a crack, good agreement between the sensor output and crack progression during loading was also obtained in these concrete beams.

Sensing Applications for Plastic Optical Fibres in Civil Engineering

“…Kuang et al [13] conducted a series of flexural tests on scaled-specimens where the POF sensor was attached to the bottom surface of the concrete beams and demonstrated in their study that the POF sensor design used were of sufficient sensitivity to detect the presence of hair-line cracks. Figure 5 shows photomicrographs of the size of the cracks in the concrete relative to the POF.…”

“…6. Plots showing the ability of the POF sensors in detecting the crack for a series of six scaled concrete specimens (after [13]). …”

Effect of Tensile Reinforcement Ratio on the Effective Moment of Inertia of Reinforced Lightweight Concrete Beams for Short Term Deflection Calculation

“…These moments corresponding to deflection ∆ cr , ∆ y , and ∆ u as can be seen in Figure 2. The technique adopted above is more convenient which give sufficient results in terms of M y evaluation instead of using moment-curvature relationship that need strain measurement of concrete and tensile reinforcement of the beam [22].…”

Pitted Corrosion Detection of Thermal Sprayed Metallic Coatings Using Fiber Bragg Grating Sensors

“…The Fiber Bragg grating (FBG) sensor, due to its high sensitivity, resistance to electromagnetic interference, good durability, low cost, and more importantly capability of real-time monitoring, has become a widely accepted sensing alternative for strain [27][28][29], temperature [29][30][31], and possibly crack measurements [32,33] in civil engineering fields. Studies of using FBG sensors in crack detection on concrete and metallic structures had shown that distinguishable data alter could be observed when cracks initiated.…”