This study investigates the use of a Fiber Bragg Grating (FBG) sensor to measure strain in Carbon Fiber Reinforced Polymer (CFRP)-strengthened concrete beams. Finite element analysis in Abaqus™ simulates three-point bending tests to compare the behavior of Reinforced Cement Concrete (RCC) and CFRP beams under mechanical and thermal loading. The objective is to evaluate deflection progression until crack initiation. Simulations reveal that CFRP beams exhibit an 86% reduction in stress and strain fluctuations compared to conventional RCC beams. FBG sensor data from numerical models show strain sensitivities of 1.81 µm/µƐ for RCC and 1.21 µm/µƐ for CFRP beams, confirming the sensor’s effectiveness in monitoring structural response.Thermal strain sensitivity of the simulated sensors is 1.72 nm/°C for RCC beams and 1.19 nm/°C for CFRP beams. CFRP-strengthened beam showed a significantly reduced displacement of 0.0727 mm. The proposed FBG strain sensor can be used to measure micro strains with small amplitudes in harsh environments.