An optical fiber sensor system for remote displacement monitoring of structures - Prototype tests in the laboratory

This study describes a new optical fiber monitoring system to measure structural displacements. The underlying concept is based on a square fiberglass 'Smart Rod' containing grooves in each face, glued into which are optical fibers containing fiber Bragg gratings (FBGs) at a succession of points along their length. The Smart Rod is rigidly fixed at discrete points to the structure being assessed and the strain at each FBG is determined optically. The strain is thereafter converted to structural displacements. This study describes a series of 'bench test' laboratory experiments designed to explore the challenges of installing the monitoring system and interpreting the results. The results from the tests are presented and discussed in the context of the accuracy achievable with the proposed system. The tests have shown that the Smart Rod is sensitive enough to measure rotational movements of 0.5 degrees and lateral movements of 0.1 mm of the fixings in the laboratory. Recommendations are consequently made for a practical instrumentation system based upon the Smart Rod. An example is provided showing the Smart Rod installed in a road tunnel to monitor displacements of the tunnel lining.