Fiber Optic Sensors as NDT Tool for Structural Monitoring

Structural monitoring is used as a diagnostic tool for detecting or inferring the presence of defects/damages and for scheduling maintenance operations. It has become important to determine the safety of the critical structures by the Non-Destructive Testing (NDT) for evaluation of their strength and integrity. This assessment is essential for the repair, retrofit, rehabilitation, life extension, or replacement of the structure in question. Fiber optic sensors are attractive sensing devices as an NDT tool; given their small size, light weight, and dielectric glass construction that renders them immune to electrical noise and electro magnetic interference. Optical fibers offer the possibility to be embedded within cement or concrete without affecting their performance and used as sensitive, but rugged, transducers of mechanical perturbations. Fiber optic sensors have the capability to be embedded prior to curing, into the concrete structural elements for non-destructive evaluation of structural integrity and the measurement of the internal state of stress. Sensors can also be surface mounted on concrete or steel members. There are challenging problems and issues while applying fiber optic sensing technology for monitoring of concrete structures. Systematic studies on the new sensors have been carried out in the laboratory to solve the following issues/problems: 1. Safe embedment of fiber optic sensors in concrete structures 2. Elimination of errors due to temperature induced apparent strain 3. Assessment of performance of the sensors under static and cyclic loading 4. Assessment of the long term stability of the fiber optic sensors In this paper, the potential of fiber optic sensors for monitoring concrete structures has been highlighted. Details of the laboratory studies carried out in solving some of the technical challenges and issues for implementing the fiber optic sensing technology to the field problems are also covered.