Experimental verification of DAS vibration response characteristics of equal strength beam under sinusoidal excitation.

Distributed Acoustic Sensing (DAS) technology holds great potential for structural dynamic monitoring; however, its quantitative capability for complex dynamic strain fields and the reliability of spatial resolution require systematic verification. This study employed a systematic "theoretical modeling-simulation analysis-experimental verification" approach, using an equal-strength beam under sinusoidal excitation to investigate the dynamic response characteristics of DAS. A complete dynamic strain transfer model from external excitation to DAS phase-change signals was established, defining the phase sensitivity coefficient as a key parameter for quantitative analysis. Finite element simulations revealed that while the beam's strain is approximately uniform at low frequencies (< 5 Hz), it exhibits a gradient distribution-large near the fixed end and small near the free end-near the natural frequency, departing from the static "equal-strain" characteristic. Experimental results under 5 Hz excitation, utilizing synchronized measurements from accelerometers, FBG sensors, and DAS, demonstrated that DAS accurately captures the dominant vibration frequency. The measured phase sensitivity coefficient showed only a 7.3% error relative to theory, the response amplitude maintained high linearity with excitation and reference signals (R² ≥ 0.99), and the phase delay was negligible (0.02 rad). By incorporating the spatial averaging effect of the DAS gauge length, the theoretical strain ratio across channels is corrected, reducing the deviation from 23.4% to 1.7%, confirming DAS's ability to quantitatively resolve spatial differences in dynamic strain distribution. Additional 50 Hz experiments validate the frequency applicability threshold and demonstrate DAS's utility for event detection beyond the uniform-strain regime. Furthermore, by comparing DAS channel response ratios across spatial positions with theoretical strain ratios, the study confirmed DAS's ability to quantitatively resolve spatial differences in dynamic strain distribution. This work systematically validates the quantitative accuracy and reliability of DAS as a distributed dynamic strain sensing tool, and the revealed dynamic-static strain distribution differences, together with the established validation methodology, provide solid theoretical and experimental support for refined DAS-based monitoring in engineering structure dynamic monitoring scenarios.