In this study, a method to measure multi-point displacement responses by using a digital image processing technique is suggested. Digital images are acquired by a commercial digital camcorder, which is the sensor to measure remote displacement responses considering convenient and economical aspects for use. The digital image correlation (DIC) as one of digital image processing techniques is applied to the algorithm developed and the image transform function (ITF) to correct the movements and errors between the image without deformation and that with deformation is also used to increase the resolution of displacement responses. One shaking table test and several field tests to validate this algorithm, which can measure multi-point displacement responses of structures by using digital image processing techniques, were carried out. Structural characteristics of existing civil infrastructures may generally differ from those of their initial design stage.

As an alternative to reduce the installation expenses and enhance the reliability of measured data, a method to measure the displacement responses in a remote distance without attaching sensors is needed. Many studies (Kwon et al. 2002; Kim and Kwak 2005; Lee and Shinozuka 2006; Ji and Chang 2008) have been conducted using camera visual signals instead of conventional contact type displacement sensors. However, these studies have been focused on measuring displacement response by a digital image processing technique after recording a position of the target attached on the structure, in which a number of measurement targets may be limited.