Motion adaptive vision-based vibration measurement and modal identification for the roof masts of a tall building

On May 18, 2021, occupants in Saige Plaza Building felt significant building motions together with its roof masts caught in obvious vibrations (May 18 vibration event), which were recorded by a surveillance camera installed on the roof of the building. This study aims to investigate the vibration characteristics of masts by processing the video data using computer vision technique. A motion adaptive vision-based vibration measurement method (M-DAVIM) is firstly proposed, focusing on dealing with the adverse motion effects of the camera itself on measuring dynamic displacements. The M-DAVIM incorporates time-domain and frequency domain correction procedures to reduce noise caused by camera self-vibration, and utilizes a CNN-based object tracking method to search objects that blurred by camera shaking. Indoor periodic vibration tests and field tests of photovoltaic panels demonstrated that M-DAVIM outperforms previous vision-based methods in accurately measuring displacements under unfavorable conditions, such as target rotation, motion blurring, and background interference. The proposed M-DAVIM was then applied to measure the dynamic displacements of the roof masts of Saige Building and identify their modal parameters (frequencies and damping ratios) based on the limited video data. A vibration component of 7.60 Hz was identified as the camera self-vibration and was effectively corrected by the M-DAVIM method. Based on finite element analysis and given the wind condition, the twin-mast might mainly experience the vortex-induced vibration at 2.12 Hz with two masts vibrating synchronously in-plane along opposite directions during May 18 to 22, 2021. This study demonstrates the robustness and effectiveness of the M-DAVIM and shows its potential application for long-term field monitoring of large-scale structures under severe outdoor environments.