A non-contact vision-based system for multipoint displacement monitoring in a cable-stayed footbridge

Abstract

SummaryVision-based monitoring receives increased attention for measuring displacements of civil infrastructure such as towers and bridges. Currently, most field applications rely on artificial targets for video processing convenience, leading to high installation effort and focus on only single-point displacement measurement, for example, at mid-span of a bridge. This study proposes a low-cost and non-contact vision-based system for multipoint displacement measurement based on a consumer-grade camera for video acquisition and a custom-developed package for video processing. The system has been validated on a cablestayed footbridge for deck deformation and cable vibration measurement under pedestrian loading. The analysis results indicate that the system provides valuable information about bridge deformation of the order of a few centimetres induced, in this application, by pedestrian passing. The measured data enable accurate estimation of modal frequencies of either the bridge deck or the bridge cables and could be used to investigate variations of modal frequencies under varying pedestrian loads. KEYWORDSbridge displacement, cable vibration, cable-stayed bridge, pedestrian loads, vision-based system | INTRODUCTIONStructural health monitoring is aimed at providing valuable information about structural performance and characterisation of structural defects to the asset owners, especially for those civil infrastructures beyond the design life. Vibrationbased modal tests are a common way for structural condition and serviceability assessment, providing a direct view about the structural stiffness, mass properties, and their distributions. [1] As well as for validating designs of civil structures, modal parameters extracted from vibration data obtained in short-term or long-term measurements are widely believed to have potential for identifying changes in structural condition or "damage." [2] The sensitivity of these parameters to damage depends on the nature of the damage, for example, local deterioration of material, for example, due to corrosion, may not be detectable against background effects of environmental variability, whereas boundary conditions are known to have a relatively strong effect, for example, fixity of bridge supports.[3]This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

A Novel Dense Full-Field Displacement Monitoring Method Based on Image Sequences and Optical Flow Algorithm

“…According to Equations (11), (14), and (15), optical flow vectors t i to t i+1 can be calculated, and all time u i and v i can be summed to calculate the displacement of the pixel point.…”

“…Displacement is an important index of structural state and performance evaluations [7]. The static and dynamic characteristics of a structure, such as bearing capacity [12], deflection [13], deformation [14], load distribution [15], load input [16], influence line [17], influence surface [18], and modal parameters [19,20], can be calculated by structural displacement, to convert them further into physical indicators of response for structural safety assessment.…”

A Plastic Optical Fiber Sensing System for Bridge Deflection Measurement

“…Feng et al [16] developed a subpixel template matching technique based vision sensor system for non-contact measurement of structural displacement. Xu et al [17] proposed a low-cost, vision-based system for multipoint displacement measurement using a consumer-grade camera for video acquisition and a custom-developed package for video processing. However, there are still lots of problems with this system, such as difficulties with stable camera mounting [18], measurement errors derived from lighting changes [19], and light refraction caused by atmospheric effects, especially for long-range measurements.…”

Image processing–based real‐time displacement monitoring methods using smart devices

“…In recent years, the global position system (GPS), laser Doppler vibrometer, and LiDAR have emerged as new, noncontact measurement techniques; however, their applications are still challenging because of their high cost. In the meantime, alongside the advancement in information–communication innovations, enhancements in image‐capturing devices, and the development of new post image processing algorithms, vision‐based structural vibration measurement is becoming standout among the well‐known noncontact measurement methods in civil engineering applications . These systems are comparatively cheaper and reduce the difficulties in installation procedures.…”