Abstract
An advanced video deflectometer using actively illuminated LED targets is proposed for remote, real-time measurement of bridge deflection. The system configuration, fundamental principles, and measuring procedures of the video deflectometer are first described. To address the challenge of remote and accurate deflection measurement of large engineering structures without being affected by ambient light, the novel idea of active imaging, which combines high-brightness monochromatic LED targets with coupled bandpass filter imaging, is introduced. Then, to examine the measurement accuracy of the proposed advanced video deflectometer in outdoor environments, vertical motions of an LED target with precisely-controlled translations were measured and compared with prescribed values. Finally, by tracking six LED targets mounted on the bridge, the developed video deflectometer was applied for field, remote, and multipoint deflection measurement of the Wuhan Yangtze River Bridge, one of the most prestigious and most publicized constructions in China, during its routine safety evaluation tests. Since the proposed video deflectometer using actively illuminated LED targets offers prominent merits of remote, contactless, real-time, and multipoint deflection measurement with strong robustness against ambient light changes, it has great potential in the routine safety evaluation of various bridges and other large-scale engineering structures.
Highlights
Bridge deflection is an important parameter in safety examination of bridge structures, which reflects the overall stiffness of the bridge structure and is closely related to its bearing capacity and the ability to resist dynamic loadings such as traffic, gusts and earthquake
With the aid of the state-of-the-art subpixel registration algorithm, the video deflectometer is able to provide real-time and high-accuracy deflection measurement provided that the texture on the test bridge has sufficient and constant intensity contrast during the whole measurement period
Compared with traditional contacting displacement measurement techniques, the video deflectometer has the advantages of compact configuration, ease-of-use, as well as remote, real-time, and multipoint deflection measurement
Summary
Bridge deflection is an important parameter in safety examination of bridge structures, which reflects the overall stiffness of the bridge structure and is closely related to its bearing capacity and the ability to resist dynamic loadings such as traffic, gusts and earthquake. The most widely used bridge deflection measuring techniques are level gauges and displacement meters, which are relatively accurate, but in general can only be applied to measure static deflection, and are not suitable for continuous dynamic measurements These conventional techniques must be operated manually rather than automatically. Despite the diversity of non-contact deflection measurement techniques, vision-based optical techniques have received increasing attention due to their outstanding advantages, such as low-cost and easy-to-use setup, multipoint real-time measurement and visualization, and wide range of resolution and applicability. With the aid of the state-of-the-art subpixel registration algorithm, the video deflectometer is able to provide real-time and high-accuracy deflection measurement provided that the texture on the test bridge has sufficient and constant intensity contrast during the whole measurement period. Compared with traditional contacting displacement measurement techniques, the video deflectometer has the advantages of compact configuration, ease-of-use, as well as remote, real-time, and multipoint deflection measurement. An Advanced Video Deflectometer for Real-Time, Remote Bridge Deflection Measurement
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