Distributed Strain Measurement along a Concrete Beam via Stimulated Brillouin Scattering in Optical Fibers

Romeo Bernini,1 Aldo Minardo,2 Stefano Ciaramella,3 Vincenzo Minutolo,4 and Luigi Zeni5
1Istituto per Il Rilevamento Elettromagnetico Dell Ambiente, Consiglio Nazionale Delle Ricerche, Naples, Italy
2Department of Information Engineering, Second University of Naples, 81031 Aversa (CE), Italy
3Dipartimento di Ingegneria Civile, Seconda Università di Napoli, Via Roma, 29 81031 Aversa, Italy
4Seconda Università di Napoli, Via Roma, 29 81031 Aversa, Italy
5Istituto Nazionale per la Fisica della Materia, Trieste, Italy

Received 18 January 2011; Accepted 25 February 2011

Academic Editor: Francesco Soldovieri

Romeo Bernini, Aldo Minardo, Stefano Ciaramella, Vincenzo Minutolo, and Luigi Zeni, “Distributed Strain Measurement along a Concrete Beam via Stimulated Brillouin Scattering in Optical Fibers,” International Journal of Geophysics, vol. 2011, Article ID 710941, 5 pages, 2011. doi:10.1155/2011/710941

Abstract

The structural strain measurement of tension and compression in a 4 m long concrete beam was demonstrated with a distributed fiber-optic sensor portable system based on Brillouin scattering. Strain measurements provided by the fiber-optic sensor permitted to detect the formation of a crack in the beam resulting from the external applied load. The sensor system is valuable for structural monitoring applications, enabling the long-term performance and health of structures to be efficiently monitored.

1. Introduction

Structural health monitoring systems have the potential to reduce operational maintenance costs by identifying problems at an early stage, and to verify the effectiveness of repair procedures. Moreover, monitoring systems help increase understanding of the real behavior of a structure, such as a bridge, and aid in planning maintenance interventions. In the long term, static monitoring requires an accurate and very stable system, which can relate deformation measurements taken over long periods of time [1]. Strain measurement with a distributed Brillouin scattering-based sensor system provides excellent opportunity for the health monitoring of civil structures [2–4]. It allows measurements to be taken along the entire length of the fiber, rather than at discrete points, by using fiber itself as the sensing medium.

Distributed optical fiber sensors based on stimulated Brillouin scattering (SBS) rely on the interaction between two lightwaves and an acoustic wave in the optical fiber. The measurement principle is based on the characteristic that the Brillouin frequency of the optical fiber is shifted when strain as well as temperature changes occur. Spatial information along the length of the fiber can be obtained through Brillouin optical time domain analysis (BOTDA) by measuring propagation times for light pulses travelling in the fiber. This allows for continuous distributions of the measurand to be monitored. This type of sensing has tremendous potential for structural monitoring. These systems offer unmatched flexibility of measurement locations and the ability to monitor a virtually unlimited number of locations simultaneously.

In this paper, we report a number of experimental measurements carried out along a 4 m-long concrete beam subjected to a variable load, by the use of a portable BOTDA sensor. A single-mode optical fiber was attached to the beam in order to detect both tensile and compressive strains. Two different adhesives were employed, in order to compare them as regards their efficiency in transferring the strain between the structure and the fiber core. The sensor was able to detect the formation of a crack in the midsection of the beam, consequent to the application of an external load.

2. Experimental Results

3. Conclusions

References

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