High-speed Vision System for Dynamic Structural Distributed Displacement Analysis

Structural health monitoring (SHM) has become prominent topic in the field of civil engineering in detecting structural damage, estimating remaining service life of structure, optimizing decision making process on maintenance, and aiding performance-based structure design methodology. Dynamics measurement is one of important techniques to diagnose deterioration of structures by inspecting their dynamics properties, mainly derived from displacement time-series from multiple measurement points. Various conventional distributed displacement measurement techniques of civil structures currently in place have been limited due to various constraints: inadequate accuracy, overly-localized measurement point, measurement drift, robustness issue on field usage, structural obstruction, and reliability for long-term installation. Optical technique utilizing LED markers has been proposed as an alternative for dynamic distributed displacement measurement, providing visual cue and and easily-identifiable marker position. The technique incorporates high-speed camera system and telephoto lens to capture both lateral and vertical displacement of bridge members, LED markers to cope with the insufficient incident light over long distance and small camera aperture, and computer vision system to calculate multiple markers' displacement simultaneously. Further analysis was conducted to evaluate structure natural vibration frequencies using FFT (Fast Fourier Transporm) peak-picking method.