Surface Rotation Correction and Strain Precision of Wide-Angle 2D DIC for Field Use

Abstract

The paper describes how two-dimensional (2D) digital image correlation (DIC) is used on underneath surfaces of concrete bridges with a wide-angle-lens camera during load testing, and how it has potential as a stop criterion in proof loadings. A method is proposed for correction of out-of-plane deflection including rotation of the surface. The method is applied to laboratory tests, using well-defined circular speckle patterns, as well as to a field-tested bridge (on raw concrete). The proposed correction corresponds to the level of pseudo strain but is very sensitive to precise surface deflection measurements. In the laboratory tests, a strain precision of the wide-angle-lens camera is compared to a regular-lens camera. The parametric study concludes that a pattern pixel relation (PPR), in the interval from four to nine pixels per pattern circle diameter, provides the optimal precision regardless of the camera type. The field-tested bridge has less good precision compared to most parameter combinations of the laboratory tests. Nevertheless, the field strain precision has potential for improvement based on results from the laboratory tests.