Vision-Based Large-Field Measurements of Bridge Deformations

Abstract

A high-resolution digital image correlation (DIC) system was developed for monitoring bridge deformations under load testing. Significant advantages of the new system compared with contact-instrument based systems include its relative low cost, ease of operation, speed of setup, ability to monitor any point over a large field of view in a single setup, and its relatively high accuracy. The civil infrastructure vision (CIV) system consists of two high-resolution low-noise digital cameras and a DIC software coded by the authors. It can track the three-dimensional (3D) spatial movement of any visible target on the surface of a bridge to a resolution on the order of 1/40th of a millimeter (1/1,000th of an inch), even when the cameras are over 30 m (100 ft) away from the bridge. The accuracy of the CIV system is quantified using certified gage blocks over the full measurement volume encompassing sight distances between 12.2 m (40 ft) and 33.5 m (110 ft). System accuracy is further validated through two field studies by comparing deflection measurements obtained using the system with those obtained by displacement transducers attached to the underside of bridges. In Field Study 1, a multigirder steel bridge was monitored during applied truck loading using traditional instrumentation and the CIV system. In Field Study 2, a multicell concrete culvert was monitored under truck loading. In both field studies, the deflection readings obtained by the CIV system were comparable to those obtained from traditional instruments.