A simple image‐based strain measurement method for measuring the strain fields in an RC‐wall experiment

Abstract

SUMMARYA simple image-based method for measuring plane strain fields on the surface of specimens in earthquake engineering experiments was developed. This method integrated camera calibration, stereo triangulation, image metric rectification and image template matching techniques to develop a method that was costeffective, easy to apply and provided a satisfactory level of measurement accuracy. A zero-strain test conducted using this method showed that the measurement accuracy achieved was 0.04 pixels. That is, the relative displacement accuracy achieved was 0.005 mm and the strain accuracy was 0.001. This level of accuracy was achieved using eight-mega-pixel digital cameras to measure a 17 cm×28 cm measurement region. Cracks that were 0.012 mm wide were identified in the concrete by examining the displacement fields calculated through the application of this image-based method in an RC-wall experiment.

Thin crack observation in a reinforced concrete bridge pier test using image processing and analysis

“…This study maintains that the observed region surface of the pier is approximately a cylinder, and any spurious deformation of this property is ignored as we focus on crack observation rather than accurate strain field measurement. This method can be adjusted for other shapes of structures, e.g., walls [10] or rectangular pillars.…”

“…The speckle spray method, which applies random speckles and texture patterns over a surface, has been widely used in past image measurements in structural experiments (e.g. Carroll et al [9] and Yang et al [10]). However, speckle painting may increase the difficulty of crack observation by the naked eye.…”

“…The control points in the first pair of photos (initial photos taken by the left and right cameras) are selected manually by the user (e.g., using a computer mouse). The control points in later pairs of photos (those of the deformed specimen) are positioned automatically by image tracing using sub-pixel precision template matching [10], which is a modified version of template matching function in the OpenCV library [11]. After the control points are positioned in the image coordinates (i.e., pixel positions in photos), their 3D coordinates can be estimated by stereo triangulation [14].…”

Strain measurement using 3D stereo image correlation

“…This method provides an efficient means of strain measurement. A new technique [2] for strain measurement is the imagebased method in an RC-wall experiment. This technique of strain measurement plays an important role in the field of earthquake engineering equipment.…”

Particle image velocimetry (PIV) to evaluate fresh and hardened state properties of self compacting fiber-reinforced cementitious composites (SC-FRCCs)

“…All of these equipments are effective and trustworthy if they are accordingly used with a proper loading set-up and system. However, there are typical drawbacks faced with the use of these conventional measurement devices, such as; (i) they provide only one measurement at a time, either strain or displacement [5], (ii) problems due to proper bonding of the strain gauges, (iii) de-bonding during the loading of the specimen, (iv) alignment of the strain gauge with the fibers when using strain gauges on composite materials [5], (v) tedious and time-consuming sample surface preparation and the strain gauge adhesion [6], (vi) complexity and impracticity of using too many strain gauges when the region of interests is a large one [7,8], (vii) the points measured by these conventional measurement devices cannot be dense and well distributed [9], deformations can only be measured at points where devices are mounted and in many cases would not cover the entire surface [10,11], (viii) possible damages to the measuring devices during the experiment, (ix) problems related to removal of the devices prior to specimen failure to avoid damage to the instrument, (x) high cost of measuring devices, and extra charges for data acquisition [12]. As a result, these drawbacks of conventional measurements have led researchers to develop non-contact full field deformation measurement techniques.…”