Crack monitoring on concrete structures: Comparison of various distributed fiber optic sensors with digital image correlation method

Abstract

The quality of strain measurements using distributed fiber optic sensors (DFOS) depends largely on the bond between the host material and the optical fiber. Experimental investigations were carried out to test the suitability of five different DFOS types for crack monitoring. The DFOS were subsequently bonded to two 4 m long reinforced concrete (RC) beams, so that the influence of the application technique could be evaluated. DFOS measurements were verified by digital image correlation (DIC) and electrical strain gauges (SGs). For the different DFOS types, clear differences in the measured strain curves and determined crack widths were observed. The focus was on two robust DFOS, which can be deployed on construction sites. Compared to the layered sensing cable, a monolithic DFOS showed a clear strain distribution with pronounced strain peaks even for closely spaced cracks. The crack widths obtained by integrating the strain curves showed high agreement with DIC measurements.

Crack monitoring on concrete structures with distributed fiber optic sensors—Toward automated data evaluation and assessment

“…Already existing crack width calculation approaches tailored for DFOS measuring reinforcement strains 8 and concrete strains 9 are contrasted. Supplementary to a related study, 10 which focuses on the influence of the DFOS type for successful crack monitoring, this study focuses on methodology of the data analysis of the experimentally gained data.…”

“…[3][4][5][6] The RAYLEIGH-scattering based coherent optical frequency domain reflectometry is a distributed strain sensing (DSS) technology, which makes quasi-continuous strain measurements with high spatial resolution over extended ranges possible. 3,[7][8][9][10] Small in size, lightweight and cost-effective, distributed fiber optic sensors (DFOS) are a promising sensing technique for deployment on site. 3,11 Great potential is offered by the quasi-continuous data for SHM, especially for monitoring from the beginning of a structure's existence, where it is not clear when and where damages will occur.…”

“…12,13 Because choosing the right DFOS for the specific measurement task is not trivial, several studies compare the suitability of different DFOS types and application methods for crack monitoring. 10,[14][15][16] For crack monitoring, the DFOS must be robust to withstand the rough building site conditions (e.g., mechanical impact during concreting). At the same time, it must be sufficiently sensitive to reliably detect cracks and yet flexible to some extent so that DFOS breakage does not occur as a result of the emerging cracks.…”

Towards an Automated Crack Monitoring using Distributed Fiber Optic Sensors

“…Another -"middle"-approach -is to determine the transfer length as the half distance to the neighboring cracks [12] [24]:…”

openLAB – Eine Forschungsbrücke zur Entwicklung eines digitalen Brückenzwillings

“…Andererseits ermöglicht die kontinuierliche Dehnungsmessung in Verbindung mit einer hohen Ortsauflösung die Analyse lokaler Effekte. So ist es beispielsweise möglich, Risse anhand lokaler Dehnungsspitzen im Messsignal sowohl ortsgenau zu detektieren als auch deren Rissbreiten präzise zu bestimmen[44][45][46][47][48]. Ein Vorgehen zur automatisierten Rissüberwachung mittels DFOS[49] besteht aus den Schritten (i) Datenakquise, (ii) Vorverarbeitung, (iii) Rissdetektion, (iv) Festlegung der Integrationsbereiche, (v) Kompensation von Störeinflüssen und (vi) Rissbreitenberechnung durch numerische Integration des Dehnungssignal innerhalb der Einflusslänge eines Risses.…”