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Thanks to the capabilities of distributed fibre optic sensors (DFOS), a significant increase in their applications within civil and geotechnical engineering has been observed during the last few years. In contrast to conventional spot gauges, the main advantage of this technology is direct damage detection, as the information is gained over the entire measurement path. This diagnostic solution is especially suitable for safety-critical infrastructure, including bridges. However, to utilise the benefits of the DFOS approach, appropriate interrogators, sensors, and installation methods must be adopted. The article briefly discusses possible solutions available on the market, indicating their specific advantages and limitations. Then, several practical case studies related to bridge monitoring in Poland are presented. The review shows various possible applications, from long measurement sections over entire spans to small-size structural components. Some are truly new and pioneer solutions, solving different technical problems in bridge engineering. Presented applications supported by in situ data proved the possible high-quality performance of DFOS-based systems for measurements of concrete, steel and composite bridges in actual operating conditions. [ABSTRACT FROM AUTHOR]

The article presents research on the performance of different distributed fibre optic sensing (DFOS) tools, including both layered cables and monolithic composite sensors. The main need for the presented research was related to the growing applications of the DFOS techniques for the measurements of cracked concrete structures. There are no clear guidelines on the required parameters of the DFOS tools, which, despite their different designs, are offered for the same purpose (strain sensing). The state-of-the-art review and previous experiences show noticeable differences in the quality of the results depending on the applied DFOS tool. The technical construction of selected solutions was described with its theoretical consequences, and then laboratory tests on full-size reinforced concrete beams were discussed. Beams equipped with embedded tools were investigated in four-point bending tests, causing the formation of multiple cracks in the tension zone along the beams' length. The results in the form of strain profiles registered by selected DFOS tools were analysed regarding the qualitative (crack detection) and quantitative (width estimation) crack assessment. The comparison between crack-induced strain profiles was based on a new parameter called crack shape coefficient CSC, which could be applied to assess the effectiveness of the particular DFOS tool in crack detection and analysis. It was one of the world's first research allowing for such direct comparison between the layered and monolithic sensing tools. The summary indicates practical guidelines referring to the preferable design of the tools best suitable for crack measurements, as well as the field proofs based on data from two concrete bridges in Germany. [ABSTRACT FROM AUTHOR]

The article presents research on the performance of composite and monolithic sensors for distributed fibre optic sensing (DFOS). The introduction summarises the design of the sensors and the theoretical justification for such an approach. Lessons learned during monitoring cracked concrete are summarised to highlight what features of the DFOS tools are the most favourable from the crack analysis point of view. Later, the results from full-size laboratory concrete specimens working in a cracked state were presented and discussed in reference to conventional layered sensing cables. The research aimed to compare monolithic sensors and layered cables embedded in the same reinforced concrete elements, which is the main novelty. The performance of each DFOS nondestructive tool was investigated in the close vicinity of the cracks—both the new ones, opening within the tension zone, and the existing ones, closing within the compression zone. The qualitative (detection) and quantitative (widths estimation) crack analyses were performed and discussed. Finally, the examples of actual applications within concrete structures, including bridges, are presented with some examples of in situ results. [ABSTRACT FROM AUTHOR]