Abstract
The measurement of static vertical deflections on bridges continues to be a first-level technological challenge. These data are of great interest, especially for the case of long-term bridge monitoring; in fact, they are perhaps more valuable than any other measurable parameter. This is because material degradation processes and changes of the mechanical properties of the structure due to aging (for example creep and shrinkage in concrete bridges) have a direct impact on the exhibited static vertical deflections. This paper introduces and evaluates an approach to monitor displacements and rotations of structures using a novel laser and video-based displacement transducer (LVBDT). The proposed system combines the use of laser beams, LED lights, and a digital video camera, and was especially designed to capture static and slow-varying displacements. Contrary to other video-based approaches, the camera is located on the bridge, hence allowing to capture displacements at one location. Subsequently, the sensing approach and the procedure to estimate displacements and the rotations are described. Additionally, laboratory and in-service field testing carried out to validate the system are presented and discussed. The results demonstrate that the proposed sensing approach is robust, accurate, and reliable, and also inexpensive, which are essential for field implementation.
Highlights
In the last 60 years there has been a spectacular increase in bridge heritage issues
A laboratory experiment was performed to compare the proposed laser and video-based displacement transducer (LVBDT) with a traditional linear variable differential transformer (LVDT), which served as the reference measurement
A simple linear regression produced a slope of 1.026, that is, on average, the LVBDT gives displacements that are 2.6% higher compared to the LVDT displacements
Summary
In the last 60 years there has been a spectacular increase in bridge heritage issues. This approach has the same limitation as the previous one: inclinometers are already a robust, accurate, reliable and inexpensive solution This body of work is a useful starting point for the development of a video-based technology capable of capturing static and slow-varying displacements over long periods of time. It is required that the target, the projection plate, and the video camera move jointly; otherwise it is not possible to calculate the movement of the target The reason for this is that inside the field of view only the fixed reference (laser dot) is included. This paper introduces a novel sensing approach to monitor displacements and rotations on bridges and structures by combining a laser beam, a video camera, and LED lights This solution substantially improves the approach proposed by Zhao et al [25,26], eliminating the limitations explained earlier. A laboratory experiment and an in-service field test to evaluate the solution’s feasibility are presented and the results discussed
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