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 sensors are used within an integrated health-monitoring network attached to the structure. Although such sensors have been developed during the past 15 years for initial specialized applications in aerospace. hydrospace, and biomedical systems, recent attention has been given to the transitioning of these methods to the evaluation of civil structures. This paper reviews the state of the art of the application of fiber-optic sensors in the structural mechanics field and reports some of the results of an experimental study concerned with the use of embedded short-gauge-length optical-fiber sensors for the quantitative measurement of strain in reinforced concrete structures. Assessment of the validity of the measurements was accomplished through direct comparison between 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 reinforcement cage in a reinforced concrete beam-column assemblage. The fiber sensors were extrinsic Fabry-Perot interferometric elements operating at 1,300 nm. The beam-column joint was subjected to cyclic dynamic loads leading to significant strain levels. Quantitative measurements of those strains were obtained from both the fiber and foil strain gauges. Measured values of strains varied by about 5% between the two types of sensors. Results of this study indicate that properly installed fiber-optic strain gauges not only can survive the harsh environment involved in the embedment process, but can also yield accurate quantitative strain information from reinforced concrete structures.