Fiber-optic-based displacement transducer to measure bridge deflections

Abstract

Structural health monitoring is an emerging area of strategic engineering with a great potential for extending the service life of civil infrastructures and reducing their maintenance costs. In spite of the deflection measurement being one of the main parameters for assessing the real state of a bridge, the measurement techniques and the existing deflection transducers often do not respond to the necessities of structural monitoring. Therefore, a novel displacement transducer to measure bridge deflections based on noncontact measurement technique supported by the liquid leveling method was developed. The measurement of bridge deflections is performed using a hydrostatic level position along the structure as an absolute reference and without any external physical reference to the ground. Fiber-optic sensors based on fiber Bragg grating technology are the sensing units of this original bridge deflection transducer. The transducer performance obtained in a set of experimental tests has shown an accurate linear response and a very good behavior under the environmental conditions simulated in a climatic chamber. A field application at the Lezíria Bridge across the Tagus River, Portugal, evinces the ability of the present transducer to be applied in both temporary and permanent structural health monitoring systems with automatic and remote data acquisition.

Keywords

bridge monitoring deflection measurement displacement transducer liquid leveling system FBG sensors

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