Embedded Fiber Optic Crack Sensor for Reinforced Concrete Structures

A distributed fiber optic sensor is developed for embeddment in con-crete structures. The sensor principles are simple, and, therefore, practical for crack detection and deformation measurement in civil structural applications. The distributed sensor developed herein operates based on the intensity measurements of optical power. The sensor consists of a number of individual segments on one line, with gage lengths designed according to the structural and materials requirements. An optical time domain reflectometer (OTDR) is employed for interrogation of the sensor signal. The study reported herein is aimed at demonstrating the applicability of this sensor in monitoring performance of concrete structures. Crack detection methodologies were established through experiments with plain con-crete beams. Structural monitoring capability of the sensor was eval-uated through experiments with reinforced concrete beams. Experiments involved both monotonic as well as fatigue loading of the beams. The sensor was embedded in the tension zone of the beams to facilitate comparison of sensor response with visual observations. Strain gages and Bragg grating fiber optic sensors were employed for monitoring reinforcing bar strains. Experimental results are pre-sented and discussed in terms of the crack detection capability, reso-lution, and practicality of the sensor in structural applications.