The application of modern methods for bridge diagnostics and load testing

Abstract

The paper deals with the modern methods of testing and diagnostics of existing, mainly steel, bridges. The focus is on the DIC method (digital image correlation) and its application for the static measurements and dynamic measurements of the bridge deflection at high speeds and on the detection of the behavior of bridge details, such as pins and fatigue cracks. The sources of potential related error values are identified and possible strategies for the minimization of errors corresponding to the DIC field measurements are developed and described in the paper. The proposed DIC methods were successfully applied on the deflection measurement on long distances and on the measurement of the strain on details in‐situ. Relevant applications were done in the Czech Republic as a part of the bridge load testing and the results are discussed in the paper.

Digital Image Correlation for Assessment of Bridges’ Technical State and Remaining Resource

“…Among the most crucial concerns associated with the DIC measurements is the effect of out-ofplane motion, which can probably cause data corruption [16,17]. Therefore, in such a context, two approaches can be considered: 2D-DIC (planar measurements) and 3D-DIC (spatial measurements).…”

“…One of the requirements for reliable 3D-DIC measurement is a comprehensive calibration procedure to define the spatial coordinate system and the scale for all-direction displacement [17]. In Digital Image Correlation (DIC), camera calibration is a process that involves determining the intrinsic and extrinsic parameters of a camera system to accurately transform from images (pixels) to real-world coordinates in engineering units (e.g., mm).…”

“…On the other hand, cameras with lower resolution, in most cases about 2.3 megapixels, have advantages in dynamic behaviour capturing due to the possibility of increasing sampling frequency. Despite their lower resolution, these cameras maintain sufficient accuracy for recording displacement full fields during static and dynamic loading [4]. Focal length is another critical parameter, which has to be considered for optimum equipment selection and setup.…”

“…Thus, higher focal lenses ensure higher resolution, while reducing the size of the field of view (FOV). Also, the high focal length of lenses typically increases their weight, which makes them susceptible to oscillations due to wind or traffic loads [4].…”

“…In addition, possible mitigation approaches, proposed in the literature, include the introduction of optical bandpass filtering solutions [21] and subpixel tracking techniques, which partly eliminate the impact of ambient light changes [24][25][26][27]. Other ambient error sources, such as traffic-induced vibration, wind, rain, or water wave reflection can be eliminated by positioning the cameras as far as possible from the source or introducing barrier protection [17]. Furthermore, the effects of camera temperature variations can be mitigated to some extent by employing a pre-established temperature-dependent model for displacements determined in the laboratory [28].…”