Debonding and calibration shift of optical fiber sensors in concrete

Fiber optic sensors have recently be considered for strain monitoring in concrete structures. The calibration factor of the sensor depends on the strain distribution along the fiber. When an embedded fiber is under strain, debonding may occur, causing the strain distribution and hence the calibration to change, Since interfacial properties that govern debonding are sensitive to environmental conditions, the calibration factor can also change when exposed to various environments. In this paper, a theoretical framework is developed to quantify the effect of environmental conditions on calibration shift. To illustrate the application of the theoretical approach, pullout test results on specimens subjected to various environmental conditions are first analyzed to obtain interfacial parameters. With these parameters, the effects of applied strain, environmental conditions, and fiber length on the calibration factor of two kinds of fiber optic sensors are quantified with the use of a strain transfer model. Based on the results, design guidelines to minimize calibration shift can be identified.