In this paper, we study the strain transfer mechanism between a host material and an optical fiber. A new analytical model handling imperfect bonding between layers is proposed. A general expression of the crack-induced strain transfer from fractured concrete material to optical fiber is established in the case of a multilayer system. This new strain transfer model is examined through performing wedge splitting tests on concrete specimens instrumented with embedded and surface-mounted fiber optic cables. The experimental results showed the validity of the crack-induced strain expression fitted to the distributed strains measured using an Optical Backscattering Reflectometry (OBR) system. As a result, precise estimations of the crack openings next to the optical cable location were achieved, as well as the monitoring of the optical cable response through following the strain lag parameter.

The assessment of Coda Wave Interferometry (CWI) and Distributed Fiber Optics Sensing (DFOS) techniques for the detection of damages in a laboratory size reinforced concrete beam is presented in this paper. The sensitivity of these two novel techniques to micro cracks is discussed and compared to standard traditional sensors. Moreover, the capacity of a DFOS technique to localize cracks and quantify crack openings is also assessed. The results show that the implementation of CWI and DFOS techniques allow the detection of early subtle changes in reinforced concrete structures until crack formation. With their ability to quantify the crack opening, following early detection and localization, DFOS techniques can achieve more effective monitoring of reinforced concrete structures. Contrary to discrete sensors, CWI and DFOS techniques cover larger areas and thus provide more efficient infrastructures asset management and maintenance operations throughout the lifetime of the structure.

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International audienceThe article aims at detecting and quantifying early structural damages usingdeterministic and probabilistic model updating techniques. To achieve this purpose,local information in a form of optical strain measurement is employed. Thestrategy consists in updating physical parameters associated to damages, suchas Young’s modulus, in order to minimize the gap between the numerical strainobtained from finite element solves and the strain sensor outputs. Generally,the damage estimation is an ill-posed inverse problem, and hence requires regularization.Herein, three model updating techniques are considered involvingdifferent type of regularization: classical Tikhonov regularization, ConstitutiveRelation Error based updating method and Bayesian approach.An illustration of these three approaches is proposed for localizing and quantifyingan early damage in a real 8 meter post-tensioned concrete beam. Numericalresults show that all the methods properly localize the damaged areaand give similar estimation of the damage leve