Motion Magnification Based Damage Detection Using High Speed Video

Abstract

Structural system identification and damage detection is an important engineering challenge due to the increase in aging infrastructure in the United States. In order to identify a structural system or detect structural damage, measured responses of structures are used for structural identification and damage detection. Typically the acceleration response is measured, although displacement responses inherently have more information of structural dynamic behavior than acceleration or velocity. In this paper a displacement measurement methodology using high-speed video, previously proposed using the motion magnification algorithm and optical flow, is used as the input for a damage detection algorithm using an unscented Kalman filter. This noncontact displacement measurement methodology has advantages; it does not require a time consuming instrumentation process and does not add any additional mass to the structure. However, the methodology still needs improvement due to its higher noise level relative to traditional accelerometer and laser vibrometer measurements. In order to detect structural damage using displacements measured from high speed video, an unscented Kalman filter is used to simultaneously remove noise from the displacement measurement and identify the current stiffness and damping coefficient values of the structure assuming a known mass. To validate the damage detection method, a numerical state-space formulation is derived for the structural system. While traditional formulations for unscented Kalman filter based approaches require such information to predict structural parameters such as stiffness and damping, however this newly derived dynamic formation does not require external forcing information. Experimental tests are carried out to test the proposed method. Steel cantilever beams are tested with bolt-loosening of the boundary condition connection as a damage scenario. The experimental results show reasonable predictions of the stiffness and damping values compared to simple dynamic analysis calculations of the beam. doi: 10.12783/SHM2015/294