Evaluating the Effectiveness of Distributed Acoustic Sensing Technology for Strain Measurement in Steel and Steel–Asphalt Composite Beams

To develop a sensor-embedded road for traffic monitoring and autonomous driving, this study experimentally investigates the effectiveness of a distributed acoustic sensing-optical fiber (DAS-OF) system in measuring strain behavior in steel and steel–asphalt composite beams. The steel beam had an H-shaped cross section with a length of 5,400 mm, a section height (h) of 150 mm, flange width (bf) of 150 mm, flange thickness (tf) of 10 mm, and web thickness (tw) of 7 mm. Initially, a repeated loading test was conducted on the bare steel beam. In the next phase, asphalt pavement was added to the web region, and a similar test was performed. The OF cables were continuously installed along the beam length and routed through several positions in the beam section to monitor strain at multiple stations. Both the steel beam and the steel–asphalt composite beam were tested under four-point bending. Various loading values (10±0.5 kN, 10±1 kN, 10±2 kN, and 10±4 kN) and frequencies (1, 2, 5, and 10 Hz) at different spatial resolutions of the DAS-OF system (2 and 10 m) were investigated. The results obtained from the DAS-OF system are compared with those from the conventional strain and displacement gauges, as well as the bending theory. As a result, the DAS-OF system accurately captures strain distributions under low loading magnitudes by 1 and 2 kN but shows limitations in measuring the strain under higher magnitudes by 4 and 8 kN. The DAS-OF sensors exhibit decreased accuracy at higher loading frequencies (≥5.0 Hz). A short spatial resolution of 2 m provides more detailed strain measurements compared to a long spatial resolution of 10 m. The 2 m spatial resolution consistently outperforms the 10 m spatial resolution under different loading conditions, both with and without asphalt pavement. Comparisons with conventional strain gauges and bending theory calculations confirm the accuracy and suitability of the DAS-OF system for monitoring deformation in steel and asphalt pavement. Once the DAS measurement parameters were properly configured, the DAS-OF system was able to detect extremely small strains beyond the microstrain level, at which conventional strain gauges perform poorly.