The present study investigates the strain response of a Distributed Optical Fiber Sensor (DOFS) bonded to the surface of concrete structures, and aims to identify optimal conditions for crack monitoring. In a first part of the study, a Finite Element Model (FEM) is proposed to describe the strain transfer process between the host structure and the Optical Fiber (OF) core, for a specific configuration where DOFS is sealed in a groove at the concrete surface using a polymer adhesive. This approach showed that decreasing the adhesive stiffness lowers the strain transferred to the DOFS core due to load redistribution over a broader effective length, which may prevent early breakage of the DOFS trumentation, especially during crack monitoring applications. In a second part of the study devoted to experimental investigations, two mechanical tests were carried out, i.e., a compression test on a concrete cylinder and a three-point-bending test on a notched concrete prism. Both specimens were instrumented with DOFS bonded using a selection of polymer adhesives with a broad stiffness range. During mechanical tests, distributed strain measurements were collected with an interrogation unit based on Rayleigh scattering, giving access to continuous strain profiles along the DOFS. These experiments showed that strain measurements of bonded DOFS were consistent with those provided by conventional sensors (strain gauges). They also confirmed that bonding DOFS with soft adhesives allows to mitigate the amplitude of the local strain peak induced in OF core by crack opening in concrete, although adhesives with very low elastic moduli (silicone for instance) tend to reduce DOFS sensibility for early crack detection. In a last part, the FEM approach was generalized to describe the effect of crack opening on the DOFS response. Numerical simulations showed satisfactory agreement with experimental data from the bending test, and allowed to develop a simple analytical expression relating DOFS peak strain to the crack opening. In future works, such model will be helpful to optimize the design of the bonding interface layer (thickness and stiffness) allowing then a tight mechanical coupling between the concrete substrate and the sensing fiber. Keywords: polymer adhesive; Young’s modulus; distributed optical fiber sensor (DOFS); strain measurement; finite element modelling; crack opening.