Development of a digital photogrammetric system for bridge deflection measurement.

摘要

Deflection measurement can serve a very important role in evaluating the behavior of a bridge. However, traditional instruments used for bridge deflection measurement can be time consuming or disruptive to traffic. In this study, an approach using digital close-range photogrammetry with flash photography is investigated for measuring bridge deflection. The major objectives of the research were to improve the measurement accuracy and reliability while reducing field work through careful design of photogrammetry targets, camera stations, camera calibration, and network control. A thorough review of the state-of-the-art of close-range photogrammetry and case studies in the field of civil engineering was undertaken with emphasis on bridge engineering. It is concluded that close-range photogrammetry has entered a fully-digitalized stage and there is great potential for applications in the field of structural engineering.; The study focused on the investigation of four critical elements of close-range photogrammetry: network design, camera resolution, network control, and camera calibration. Bridge tests in both a laboratory and field settings were performed to evaluate the effect of the above mentioned elements on measurement accuracy. The network design proposed is based on modern photogrammetry network theory and was found suitable for bridge deflection measurement. In the evaluation of camera resolution, a Kodak DCS660 digital camera with a 6 megapixel resolution was compared with a Kodak Pro SLR/n digital camera with a 14 megapixel resolution; the two cameras were found to produce about the same measurement accuracy. The network control method, designated the "distance constraint" method, used scale bars and three reference targets set at the same elevation to define a horizontal plane. This method was shown to provide about the same measurement accuracy as the conventional "control point" method while eliminating the time-consuming total station survey of control points. Camera self-calibration (i.e., camera calibration performed using the same photographs in the actual deflection measurement) was found capable of significantly reducing systematic errors, especially for field deflection measurements.; Results of the study indicate that measurement accuracy is optimized through the careful design of the critical photogrammetry elements. Using the approach developed in this research, photogrammetric deflections measured were generally within 0.2 mm (0.008 in) of dial gage measurements based on 27 measurements in the lab study. (Abstract shortened by UMI.)