Graduate Thesis Or Dissertation
 

Use of Virtual Visual Sensors in the Determination of Natural Frequencies of Timber Structures for Structural Health Monitoring

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/st74ct865

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  • Many nondestructive techniques for structural health monitoring are subjective and based on visual observations of degradation. In addition, dynamic properties of structures are already used to obtain quantitative structural health data. However, most current data collection is limited to localized damage on the structure, rather than global response. Recent research involves the use of commercially available digital video cameras, or virtual visual sensors, to observe structural dynamic behavior. This project focuses on the determination of natural vibration frequencies by monitoring the intensity value of a single pixel coordinate over the course of a few seconds of a video of structural vibration, and then applying a fast Fourier transform to extract signal frequencies. Natural frequencies can be used to observe changes in stiffness properties of materials and structural systems that may relate to deterioration. The focus here is primarily on the development and application of the virtual visual sensor technique to wood structures to obtain information relevant to objective structural health monitoring. The experiments focus on verification of the method to extract natural frequencies in various scenarios, using the natural color gradients in wood structures to observe the motion. Additionally, effects of moisture content and simulated damage on natural frequencies are observed on simply-supported beams of dimensional lumber. Applications are also made to an in-place US Forest Service pedestrian bridge. Results show comparable accuracy in determining vibrational frequencies with virtual visual sensors and accelerometer measurements, successful observation of vibrational frequencies in a timber bridge, and good use of naturally occurring color gradients in both laboratory and field tests. Moisture content and simulated damage had measureable effects on natural frequencies using conventional accelerometers and virtual visual sensors. Digital video cameras show potential to be a promising tool for structural health monitoring of timber structures.
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