Browsing by Subject "Structural health monitoring"
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Item Open Access Design and implementation of a wireless passive sensing system for structural health monitoring(Bilkent University, 2016-06) Özbey, BurakStructural health monitoring (SHM) aims to ensure detection and prevention of damage in structures and protection of human life via observation of certain damage indicators. In SHM, one of the most important damage indicators is the strain forming on the steel reinforcing bars (rebars) embedded inside concrete. This strain can slowly develop over time, or can suddenly occur due to an overload such as an earthquake. In this dissertation, a novel wireless passive sensing system is presented for detecting and measuring the level of strain and relative displacement in structures. The sensing system comprises a nested split-ring resonator (NSRR) probe along with a transceiver antenna. These two elements form an electromagnetically coupled system that yields very high sensitivity and resolution of displacement and strain sensing accompanied with a wide dynamic range of measurement. Using this wireless system, it is possible to track strain/displacement in both the elastic (reversible-linear) and plastic (irreversiblenonlinear) deformation regions of steel rebars. In the dissertation, the results of the following experiments are presented: Characterization experiments carried out on a translation stage in laboratory environment, tensile test experiments where a rebar is loaded with a pulling force until fracture, and simply supported beam experiments where a beam undergoes loading, which leads to tensile strains on rebars at the bottom of the beam. Especially, the simply supported beam experiments constitute a decisive step toward a real-life application of the proposed sensing system. The sensing system is shown to acquire accurate data until the end of the measurements in which the wired devices such as strain gages break down and fail to capture. Furthermore, the eects of the complex electromagnetic medium formed by the rebars and the concrete on sensing are investigated. In addition, a multi-point sensing capability via multiple probes and single antenna is proposed and experimentally demonstrated, which can be used in 2-D surface strain mapping with further improvements. Finally, an equivalent circuit model is given for the NSRR structure, the results of which are compared to and found to be in good agreement with full-wave simulations and measurements. This study shows that the designed sensing system has the potential to be an alternative for both microstrain-level SHM and large displacement measurements, which can be useful for post-earthquake damage assessment.Item Open Access RF displacement and strain sensing system for wireless structural health monitoring(IEEE, 2015) Özbey, Burak; Kurç, O.; Demir, Hilmi Volkan; Ertürk, Vakur B.; Altıntaş, AyhanStructural health monitoring (SHM) is a technology with worldwide interest that is vital to ensure the reliability of any structure while also protecting the safety of human life. Over the years, a lot of research has been conducted on this topic, proposing SHM methods that may be instrumental in understanding the condition of critical parts of a structure. These methods generally rely on wired and/or active technologies, which are not preferable since the wires disallow telemetric measurements and mean increased weight and space, while the active technologies require electric power in order to operate. Two of the most important damage indices of a building structure such as a reinforcing bar (rebar) are the strain and displacement forming either with time or a sudden impact like an earthquake.Item Open Access A wireless passive sensing system for displacement/strain measurement in reinforced concrete members(MDPI AG, 2016) Ozbey B.; Erturk V.B.; Demir H.V.; Altintas, A.; Kurc O.In this study, we show a wireless passive sensing system embedded in a reinforced concrete member successfully being employed for the measurement of relative displacement and strain in a simply supported beam experiment. The system utilizes electromagnetic coupling between the transceiver antenna located outside the beam, and the sensing probes placed on the reinforcing bar (rebar) surface inside the beam. The probes were designed in the form of a nested split-ring resonator, a metamaterial-based structure chosen for its compact size and high sensitivity/resolution, which is at µm/microstrains level. Experiments were performed in both the elastic and plastic deformation cases of steel rebars, and the sensing system was demonstrated to acquire telemetric data in both cases. The wireless measurement results from multiple probes are compared with the data obtained from the strain gages, and an excellent agreement is observed. A discrete time measurement where the system records data at different force levels is also shown. Practical issues regarding the placement of the sensors and accurate recording of data are discussed. The proposed sensing technology is demonstrated to be a good candidate for wireless structural health monitoring (SHM) of reinforced concrete members by its high sensitivity and wide dynamic range. © 2016 by the authors; licensee MDPI, Basel, Switzerland.