Implementation of Digital Image Correlation for Structural Health Monitoring of Bridges

Abstract

As the civil infrastructure (e.g. bridges) of the global highway system ages, there exists a critical need for structural health monitoring over large areas that is robust, inexpensive and easily interpreted. According to the American Society of Civil Engineers, in 2008, 161,892 bridges were structurally deficient or obsolete. In the next fifteen years, nearly half of America’s bridges will exceed the typical 50- year design life. Thorough inspection of these aging bridges is important to ensure public safety. Currently, bridge health is assessed primarily using qualitative visual inspection, which is subject to variability due to an inspector’s interpretation. Instruments such as strain gages, accelerometers, fiber optic sensors, displacement transducers, etc. are becoming more common for monitoring bridge health. These sensors require external power, cabling/antenna for data transmission, high data acquisition channel counts and only measure at a discrete point or along a line (making it difficult to detect damage outside the sensor’s proximity). To rectify these drawbacks, this paper presents research results of using three-dimensional (3D) digital image correlation (DIC) as a new approach for quantitative bridge structural health monitoring. 3D DIC is a non-contact, full field, optical measuring technique that uses two digital cameras to measure surface geometry, displacement, and strain. Long term monitoring with DIC can be accomplished by imaging the bridge periodically and computing strain, displacement and surface geometry from images recorded at different dates. In this paper, DIC is shown to 1) quantify spalling by comparing subsequent surface geometry measurements, 2) monitor crack width using extensometers established between photogrammetric targets and 3) successfully locate non-visible cracks using full-field strain and displacement measurements. These techniques are first confirmed in laboratory tests. Next field measurements are made on three operational full-scale bridges. This paper also discusses the challenges and solutions to effectively implementing DIC