A Tandem Marker-Based Motion Capture Method for Dynamic Small Displacement Distribution Analysis

Abstract

This study proposes a novel vision-based measurement method to capture small dynamic displacements at many points on a large-scale structure. The measurement points are aligned in the depth direction so that all points are observable in a single field of view with a high power zoom lens. To cope with insufficient incident light and lens blur when capturing video in a limited depth of field with large magnification, our method used highly retroreflective cubes as markers, combined with a strong coaxial lighting device for measuring image displacements with a tandem-layout in images. We conducted experiments to measure dynamic displacements of a 4 m long truss bridge model, and 18 corner cubes were attached as retroreflective markers. 752×2048 images were captured with a coaxial lighting device at 240 fps. The experimental results show that the deformation of the bridge model, its resonant frequencies, and mode shapes at a frequency of dozens of Hz can be determined by analyzing images captured from a single camera view.

Single-Camera-Based Bridge Structural Displacement Measurement with Traffic Counting

“…Tandem arrangement of the optical markers along the span of a bridge with the frontal placement of the displacement measurement camera has been found to facilitate simultaneous capturing of multiple displacement measurement points from a single camera viewpoint in its depth of field, requiring no synchronization module for multiple-point measurement [ 6 ]. This could enable a simpler method of whole-span bridge displacement observation.…”

“…In this study, we introduce a single-camera-based deflection distribution measurement method with subpixel digital image correlation (DIC) analysis for a dozens-of-meters-span road bridge; this is extended from the tandem-marker-based motion capture method [ 6 ] that allows measurement of structural dynamic displacement from multiple tandem-distributed points at once without decreasing measurement accuracy by installing a front-view camera positioned with a small angular delineation to the bridge’s axis. It also enables easy-installation bridge monitoring without traffic regulation.…”