Abstract. Optical fiber measurement systems have recently gained popularity following a multitude of intensive investigations. A new technique has been developed for these measurement systems that uses Rayleigh backscatter to determine the distributed strain measurement over the total length of a fiber. These measurement systems have great potential in civil engineering and structural health monitoring. This paper addresses some preliminary comparisons between three different fiber coatings and six different adhesives on steel structures. The results are based on a bending test with specimens made of precision flat steel; optical fiber strain measurements were compared with photogrammetric strain measurements. Analysis of the test data showed a strong correlation between the optical measurement system's results and the theoretical results up to the yielding point of the steel. Furthermore, the results indicate that fibers with the Ormocer® and polyimide coatings have almost the same strain values as the reference measurement method. The main results of this investigation are a guideline describing how to attach optical fibers to steel surfaces for distributed fiber optical strain measurements and recommendations for coatings to obtain realistic strain values. Additionally, the advantages of distributed strain measurements were revealed, which illustrates the potential of Rayleigh backscattering applications.
Abstract. Distributed fiber optic strain measurement based on Rayleigh scattering has recently become increasingly popular in automotive and mechanical engineering for strain monitoring and in the construction industry, especially structural health monitoring. This technology enables the monitoring of strain along the entire fiber length. This article addresses integrating optical fibers of different coatings into the concrete matrix to measure the shrinkage deformations. However, previous studies do not give a clear statement about the strain transfer losses of fiber optic sensors in this application. In this context, three different coating types were investigated regarding their strain transfer. The fibers were integrated into fine-grained concrete prisms, and the shrinkage strain was compared with a precise dial gauge. The analysis shows a high correlation between the reference method and the fiber measurement, especially with the ORMOCER® coating. The acrylate coating used is also consistent in the middle area of the specimen but requires a certain strain introduction length to indicate the actual strain. The main result of this study is a recommendation for fiber coatings for shrinkage measurement in fine-grain concretes using the distributed fiber optic strain measurement. In addition, the advantages and disadvantages of the measurement method are presented.
Die Bedeutung von faseroptischen Sensoren hat infolge der verstärkten Strukturüberwachung (Structural Health Monitoring, SHM) von Bauwerken und Bauteilen immens zugenommen [1]. Die verteilte faseroptische Dehnungsmessung auf Basis der Rayleigh‐Streuung ist dabei ein besonders vielversprechendes Verfahren, welches eine hohe Ortsauflösung und Messempfindlichkeit an jedem Punkt der Messfaser bietet, sodass geringste Dehnungsänderungen erfasst werden können [2]. Allerdings fehlen aktuell Qualitätsstandards, die einen zuverlässigen Einsatz in der Dehnungsmessung gewährleisten. Zur Etablierung solcher Standards sind am Institut für Betonbau an der HTWK Leipzig im Zuge einer Dissertation unterschiedliche Fasercoating‐Klebstoff‐Konfigurationen für verschiedene Szenarien im Betonbau validiert worden [3]. Die Ergebnisse sind vielversprechend: Im Vergleich zu den Referenzmessverfahren zeigten die faseroptischen Sensoren Dehnungsverluste durch Coating und/oder Klebstoff von unter 5 % und damit weitaus geringere Werte als entsprechend dem bisherigen Kenntnisstand zu erwarten war.
The distributed fiber optic strain measurement based on Rayleigh scattering has recently become increasingly popular in automotive or mechanical engineering for strain monitoring and in the construction industry, especially structural health monitoring. This technology enables the monitoring of strain along the entire fiber length. This article addresses integrating optical fibers of different coatings into the concrete matrix to measure the shrinkage deformations. However, previous studies do not give a clear statement about the strain transfer losses of fiber optic sensors in this application. In this context, three different coating types were investigated regarding their strain transfer. The fibers were integrated into fine-grained concrete prisms, and the shrinkage strain was compared with a precise dial gauge. The analysis shows a high correlation between the reference method and the fiber measurement, especially with the Ormocer coating. The used acrylate coating is also consistent in the middle area of the specimen but requires a certain strain introduction length to indicate the actual strain. The main result of this study is a recommendation for fiber coatings for shrinkage measurement in fine-grain concretes using the distributed fiber optic strain measurement. In addition, the advantages and disadvantages of the measurement method are presented.
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