Debonding and calibration shift of optical fiber sensors in concrete

Fiber optic sensors have recently be considered for strain monitoring in co ncrete structures. The calibration factor of the sensor depends on the stra in distribution along the fiber. When an embedded fiber is under strain, de bonding may occur, causing the strain distribution and hence the calibratio n to change, Since interfacial properties that govern debonding are sensiti ve 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 calibratio n shift. To illustrate the application of the theoretical approach, pullout test results on specimens subjected to various environmental conditions ar e first analyzed to obtain interfacial parameters. With these parameters, t he 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 guide lines to minimize calibration shift can be identified.