Use of Distributed Optical Fibre Sensing for Structural Health Assessment of Reinforced Concrete Beams

Structural health monitoring (SHM) plays a vital role in ensuring the safety and longevity of civil infrastructure, where distributed fibre optic sensors (DOFS) offer high-resolution, full-field strain measurement capabilities. However, DOFS performance can be affected by the formation of micro-cracks in concrete, often resulting in erroneous strain data due to spectral anomalies. This study investigates the reliability of DOFS measurements under progressive loading conditions in a full-scale reinforced concrete (RC) beam. A 4000 × 200 × 400 mm3 RC beam was cast using Grade 25 concrete and reinforced with embedded DOFS along the tension rebar. Additionally, another DOFS was added to the bottom of the concrete after curing to measure strain. The beam was subjected to a four-point bending, with loading applied incrementally up to 40 kN. Strain data were acquired using an OBR 4600 system at 5 kN loading intervals. While consistent strain profiles were observed across mid-span, strain spikes and residual strains were identified on both the rebar and the bottom surface, indicating the formation of micro-cracks. Controlled rebar loading tests confirmed that adhesive bonding had negligible impact on residual strain, supporting the effectiveness of DOFS in detecting internal cracking. The findings highlight the potential of DOFS for early-stage damage detection in concrete structures.