Simplified approach for quantitative inspections of concrete structures using digital image correlation

Abstract

Periodic visual inspections are typically the primary means by which the existing condition of most infrastructure assets is assessed. The results of these inspections are inherently qualitative and subjective, and unfortunately, the recent catastrophic collapse of structures such as De La Concorde overpass in Canada have underscored the need for quantitative assessment tools to monitor crack growth and deformations over time. Conventional measurement methods present several limitations, including cost, need for a priori knowledge of critical crack locations and orientation, and exposure of sensors to harsh environmental conditions. Digital image correlation (DIC) is an optical full-field non-contact measurement technique that has been shown to be highly accurate for laboratory studies under controlled conditions and has also been successfully used for short term field tests of bridges and other structures. In this study, a simple low-cost approach is proposed to supplement periodic visual inspections with quantitative measurements using images from a handheld digital camera processed with a free DIC software. A method is introduced to correct measurement errors associated with the inevitable camera movements between photographs taken during different inspections. The approach was validated by tracking the shear crack kinematics of seven push-off specimens tested in the laboratory. After correcting for errors due to movement of the handheld camera, 98% of the 462 measurements made during the tests were within the selected tolerance limit of ± 0.1 mm compared with reference measurements made with a stationary camera equipped with a long focal length lens. These results represent a first step towards the use of the DIC technique for quantitative structural inspections for improved infrastructure management.