Synchronized IoT Framework for Vibration-Based Structural Health Monitoring of Suspension Bridges

This article presents the design, implementation, and experimental validation of an Internet-of-Things (IoT)-based structural health monitoring (SHM) system for suspension bridges using synchronized vibration measurements. The proposed framework integrates distributed micro-electro-mechanical systems (MEMSs)-based sensing nodes, global positioning system (GPS)-assisted time synchronization, low-power wireless communication, and cloud-based modal analysis to support continuous monitoring of structural conditions. The main contribution of this work is the end-to-end integration of synchronized low-power IoT sensing, multitier wireless communication, and cloud-based vibration analysis within a unified SHM framework, together with experimental validation on a laboratory-scale suspension bridge. In the proposed system, each leaf node incorporates a high-accuracy digital accelerometer, ESP-NOW communication, and a duty-cycled sleep mode to reduce power consumption, while a central gateway aggregates the acquired data and transmits them to a remote server through a cellular network. Natural-frequency analysis, mode-shape evaluation, and the modal assurance criterion (MAC) are employed to assess changes in structural dynamic behavior. The system was evaluated using a laboratory-scale suspension bridge instrumented with five synchronized IoT sensing nodes and subjected to controlled shake-table excitations. Four hanger- and main-cable-damage scenarios were introduced to evaluate the overall operation of the proposed framework. The results demonstrate successful synchronized vibration acquisition, reliable wireless data transmission, and the ability to capture damage-sensitive modal changes, including natural-frequency shifts, mode-shape distortions, and MAC variations under different damage conditions. Communication experiments further show that ESP-NOW reduces energy consumption compared with transmission control protocol/internet protocol (TCP/IP) over Wi-Fi, extending node battery lifetime by approximately 40% through sleep-mode operation. Overall, the proposed SHM framework provides a cost-effective, energy-efficient, and synchronized IoT solution for vibration-based monitoring of suspension bridges under laboratory conditions. Future work will focus on field validation on real bridge structures and long-term operation under practical environmental conditions.