DEVELOPMENT OF AN INTEGRATED WIRELESS SENSOR NETWORKS-BASED STRUCTURAL HEALTH MONITORING SYSTEM FOR BUILDINGS AND CIVIL INFRASTRUCTURES
The main purpose of this dissertation was to propose a framework for an integrated wireless sensor network (WSN)-based structural health monitoring (SHM) system in buildings and civil infrastructures. In this framework, three main parts were considered: the physical sensing; information fusion and management; and inference and decision making. To achieve this goal, an integrated WSN-based SHM system was developed. This system consists of sensing nodes, cluster head nodes, transfer node, and base station. The sensing node measures structural response or environmental parameters. Each sensing node is controlled by an Imote2 platform comprised of a microprocessor, sensor module, and communication device. To exchange information or to trigger sensing tasks, the cluster head node can communicate with sensing nodes or cluster heads of neighboring communities. The cluster head has a dual-core design that combines the Imote2 platform with a second embedded device. The cluster head has an extra wireless module and GPS. The extra wireless module provides additional RF power needed for long-range wireless communication. The GPS is useful for synchronization and localization. The transfer node functions as a coordinating node for managing cluster heads and data hopping. The base station is the highest level end device and has the largest memory, the most powerful processor and the highest communication capability. The base station node is the gateway between smart sensor networks and the Host computer. A three-tier software framework is also developed in this work serving as reliable data-sensing and transmission, data logging and data storage, user interface, data analyzing, and signal processing. Based on this software framework, a SHM application for specific purpose can be easily developed. Power sources and power consumption are the critical issue in WSN if batteries have to be periodically replaced. Hence, a novel windmill-magnet integrated piezoelectric (WMIP) energy harvesting system was also proposed. Since local and global SHM have unique benefits and shortcomings, an integrated approach may be more effective than using either approach alone. This work developed a global-local-integrated damage detection approach for localizing damage. Substructure-based frequency response function approaches were proposed for global damage detection. Local damage was then identified by Electro-Mechanical-Impedance (EMI)-Based damage detection method. Numerical and experimental study is also conducted to complete this study. Numerical results reveal that the proposed global damage detection approach can successfully locate damage at a single site and at multiple sites. Experimental analysis confirms the proposed integrated WSN-based SHM system provides excellent data sensing and transmission quality for determining the structural dynamic properties. An experimental validation in building structure confirms that the proposed global SHM approach can indicate the approximate location of the damaged area in damaged floor and the EMI-based damage detection approach can check the component of building structure locally. Subsequently, the proposed WSN-based SHM system is employed in a bridge structure to test the feasibility in field. This experimental result confirms good-quality data collection by the proposed system. In experimental period, the system shows WSN-based SHM system outperforms conventional SHM system, especially in deploying sensors. Average time for deploying single node only takes within 5min.
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