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

Abstract

Plastic optical fibres have been employed to detect initial cracks, monitorpost-crack vertical deflection and detect failure cracks in concrete beamssubjected to flexural loading conditions. The intensity-based sensor system relieson monitoring the modulation of light intensity within the optical fibre as thesensor is loaded. The sensor design offers good signal stability and sensitivity tothe monitored parameter and represents a cost-effective alternative toother more sophisticated health-monitoring systems currently used in civilengineering structures. Here, a series of three- and four-point bend tests wasconducted on a range of structures. Initially, the optical fibres were attached toscale-model concrete samples (without reinforcement) to evaluate theirability to monitor beam deflection and detect cracks. Similar tests weresubsequently conducted on life-size concrete beams containing reinforcing steelbars. The location and subsequent trajectory of cracks during the loadingregime were marked and then compared to the sensor signal to assess thesensor’s ability to monitor crack development. The results demonstrate thepossibility of using optical fibres to detect hairline cracks and ultimate failurecrack in civil engineering structures and highlight their ability to monitorcrack propagation up to ultimate failure. In addition to detecting theinitiation of a crack, good agreement between the sensor output and crackprogression during loading was also obtained in these concrete beams.