Sub-Pixel Accuracy Crack Width Determination on Concrete Beams in Load Tests by Triangle Mesh Geometry Analysis

Abstract

ABSTRACT:This paper deals with the determination of crack widths of concrete beams during load tests from monocular image sequences. The procedure starts in a reference image of the probe with suitable surface texture under zero load, where a large number of points is defined by an interest operator. Then a triangulated irregular network is established to connect the points. Image sequences are recorded during load tests with the load increasing continuously or stepwise, or at intermittently changing load. The vertices of the triangles are tracked through the consecutive images of the sequence with sub-pixel accuracy by least squares matching. All triangles are then analyzed for changes by principal strain calculation. For each triangle showing significant strain, a crack width is computed by a thorough geometric analysis of the relative movement of the vertices.

Crack Width Measurement for Non-Planar Surfaces by Triangle Mesh Analysis in Civil Engineering Material Testing

“…For each epoch, all 3D points that could be matched successfully in the current time step are triangulated into a mesh using Delaunay triangulation as it is done in (Koschitzki et al, 2011), (Liebold, Maas, 2016) and (Liebold, Maas, 2018), see Fig. 4.…”

“…In order to compute the relative translation vector in the 2D space, the algorithm from (Liebold, Maas, 2018) is applied using the point triples from Eq. 5 and Eq.…”

“…(Maas, Hampel, 2006) and (Hampel, Maas, 2009) used digital image correlation techniques to compute a dense displacement field and to analyze crack openings in horizontal and vertical profiles. (Liebold, Maas, 2018) show how to compute crack widths of concrete probes in monocular image sequences using triangle mesh analysis.…”

“…Monocular image sequences can only be used for planar surfaces and if the deformations only appear in this plane. The approach presented in this publication gives an extension to the work of (Liebold, Maas, 2018). It will be shown how to detect deformations on non-planar surfaces in triangle meshes between two epochs.…”

“…It will be shown how to detect deformations on non-planar surfaces in triangle meshes between two epochs. Herein, the triangles are transformed into 2D space using the parametrization of a known surface and are analyzed with the 2D algorithm of (Liebold, Maas, 2018). A stereo system is used to measure 3D surface points for each epoch of the sequence.…”