Field Deployment and Laboratory Evaluation of 2D Digital Image Correlation for Deflection Sensing in Complex Environments

Abstract

This study explored the application of two-dimensional digital image correlation (2D-DIC) for measuring deflections of in-service bridges. Within the emerging area of image-based structural health monitoring, this work builds from previous efforts to deploy vision-based sensing techniques for describing the operational behavior of structures. Whereas the literature includes deflection measurement systems using cameras mounted on fixed ground near the bridge span at maximum distances of approximately 300 m, this work proposes an innovative setup that enables deflection measurement in remote, offshore, and complex environments. This paper first describes a laboratory study aimed at evaluating the system performance and identifying the sources of measurement error, thus determining the level of confidence in the results and the range of applicability. The laboratory study demonstrated that the setup, designed using an inexpensive consumer-grade imaging system, had an average error consistently less than 0.2 mm (0.0075 in.). In addition, the system was deployed during a field test on a high-profile bridge structure nearly 1 mile offshore. The test program and results are presented to assess the logistics and performance of the system during load testing. Results from the study indicate the feasibility of the proposed setup for measuring deflections without a fixed ground reference.