Bridge deflection measurement using digital image correlation with camera movement correction

Abstract

When displacement measurement by digital image correlation is performed in outside for the inspection of real structures, the position and the direction of a camera are often changed slightly because of wind, oscillations and the lack of stability of ground. In order to realize the bridge deflection measurement by digital image correlation, a method for correcting the effect of camera movement is proposed in this study. The relationship between images before and after the camera movement is described by an equation of perspective transformation. The unknown coefficients of the equation are determined from undeformed regions of the images. Then, the effect of the camera movement is eliminated by using the perspective transformation. The effectiveness is validated by applying the proposed method to the rigid body rotation and translation measurement of a planar specimen, the deflection measurement of a wide-flange beam, and the bridge deflection measurement. Results show that the effect of the camera movement can be corrected by the proposed method. It is emphasized that noncontact displacement measurement is possible by simple and easy procedure with digital image correlation for the structural evaluation of infrastructures. © 2012 The Japanese Society for Non-Destructive Inspection.