A Low-Cost Cyber–Physical Sensing Architecture for Bridge Vibration-Activity Monitoring: Laboratory and Field Evaluation Under Operational Conditions

Municipal bridge management requires accessible monitoring approaches that provide objective information on vibration activity under operational conditions. This study develops and evaluates a low-cost cyber–physical sensing architecture using the Lusitania Bridge in Viña del Mar, Chile, as a case study. The system integrates four ESP32/MPU9250 sensing nodes, cascade Wi-Fi/WebSocket forwarding, a Raspberry Pi 4 gateway with an auxiliary local MPU9250 channel, and structured post-processing. Its contribution is the author-developed system-level integration and bounded field evaluation rather than the novelty of the individual components. In the laboratory shaker test, each remote node occupied 13,560 of 15,001 bins on a fixed 100 Hz grid, corresponding to a 9.61% temporal-continuity deficit; the stored-row rate was 100.023 Hz. Cross-correlation signal lags were within one to two nominal sampling intervals, but these lags are not treated as pure clock-synchronization errors. The field campaign comprised 19 short sessions collected during one experimental day. The mean session-level fixed-grid deficit was 21.04%, with values ranging from 6.83% to 44.09%, showing that end-to-end continuity was the principal operational constraint. Session S18 had the lowest deficit, 6.83%, and 214 valid 30 s windows out of 271 candidates. In S18, a higher-vibration interval showed 0.5–20 Hz band-limited RMS ratios of 1.91–2.86 and band-power increases of 5.6–9.1 dB relative to a low-activity interval. Because the sensors were mounted on the railing and no calibrated reference accelerometer was available, the results support short-duration vibration-activity monitoring and system testing, not global modal identification, damage diagnosis, warning capability, or long-term SHM.