EXPERIMENTAL-STUDY OF EMBEDDED FIBEROPTIC STRAIN-GAUGES IN CONCRETE STRUCTURES

Embedded fiber-optic sensors have the potential of providing valuable information about the condition of the host structure when these senso rs are used within an integrated health-monitoring network attached to the structure. Although such sensors have been developed during the p ast 15 years for initial specialized applications in aerospace. hydros pace, and biomedical systems, recent attention has been given to the t ransitioning of these methods to the evaluation of civil structures. T his paper reviews the state of the art of the application of fiber-opt ic sensors in the structural mechanics field and reports some of the r esults of an experimental study concerned with the use of embedded sho rt-gauge-length optical-fiber sensors for the quantitative measurement of strain in reinforced concrete structures. Assessment of the validi ty of the measurements was accomplished through direct comparison betw een the performance of these sensors and collocated foil strain gauges . Pairs of fiber sensor elements and reference foil strain gauges were attached to specific rebar elements within a three-dimensional reinfo rcement cage in a reinforced concrete beam-column assemblage. The fibe r sensors were extrinsic Fabry-Perot interferometric elements operatin g at 1,300 nm. The beam-column joint was subjected to cyclic dynamic l oads leading to significant strain levels. Quantitative measurements o f those strains were obtained from both the fiber and foil strain gaug es. Measured values of strains varied by about 5% between the two type s of sensors. Results of this study indicate that properly installed f iber-optic strain gauges not only can survive the harsh environment in volved in the embedment process, but can also yield accurate quantitat ive strain information from reinforced concrete structures.