Long-gauge fibre optic sensors: performance comparison and applications

Abstract

Long-gauge deformation sensors have opened new possibilities for the health monitoring of civil engineering structures. They are particularly suitable for applications in structures built of inhomogeneous materials, such as concrete, and with complex strain fields, such as bridges, buildings, dams, whenever the global structural behaviour assessment is of the interest. Different technologies and measurement principles have been developed for measuring average strains over measurement bases that can reach tens of meters with resolutions in the micrometer range. In this work, the performances of seven commercially available alternative solutions, based on fibre Bragg-grating, Fabry-Perot interferometry, stimulated Brillouin scattering, low-coherence interferometry and traditional vibrating-wire technology, were tested and directly compared both in laboratory and in field conditions. The results are presented and discussed, aiming at the assessment of the main characteristics of each technology, and taking into account the principal requirements of in-field civil engineering applications. The efficiency of a monitoring method based on long-gauge sensors is illustrated through an application at the Ricciolo Viaduct in Switzerland.

Investigation on Low Cost Optical Fiber Sensor Interrogator

“…The derivative of the above FSR equation is: (4) We used FFT to find the period in order to get the FSR, and then further went to find the deformation and displacement. If L is around 0.66 mm, and assuming that the frequency test error is about 10 pm in wavelength which is about 125 MHz in frequency, which will lead to a maximum displacement test error of about: ~0.005 mm from Eq.…”

“…An optical switch is for the purpose of time multiplexing to decode more sensors. For the FBG sensor, it can find the peak FBG wavelength through peak tracing algorithms [4,5]. But for SOFO sensor mode, there is typically an interference pattern across the full scanning spectral window, thus we need to use the following new algorithm.…”

“…However, usage of optical fiber sensors (OFS) has been increasing greatly in the recent years as sensors for strain and temperature in the SHM applications worldwide [1][2][3]. Compared to other sensing systems, OFS possess specific advantages: higher accuracy and sensitivity, compact sizes, light weight, immunity to electromagnetic interference noise, safe for usage, resistance to environmental and chemical corrosion, and distributed sensing over long distances [4][5][6].…”

Static load testing with temperature compensation for structural health monitoring of bridges

“…In this work, static deformation was measured by displacement sensors, which was here an easy and reliable solution. Furthermore, long-gauge deformation sensors may be an interesting alternative as they cover the whole volume of a structure enabling a global monitoring with high resolutions [19].…”

Comparison between point and long‐gage FBG‐based strain sensors during a railway bridge load test

“…or installation (embedded or fixed to the surface), the fiber must be prestressed if it is to measure compression strain correctly, as if not it may warp even under small compression loads. Almost all long‐gage sensors presently available e.g., are prestressed and generally give good results in different applications . However, pre‐stressing is a delicate operation that requires at least two people and the following conditions: (a) the pre‐stressing may be lost (the fiber can slip from its anchorage, temperature variations, etc.)…”