Structural Analysis of Constructions by Means of Automatic Crack Parameterisation Based on Photographs

Constructions can show cracks due to mechanical stress. Such cracks have been investigated for decades by means of mapping and manual measurement of crack widths. During the formation of a crack, the flanks separate from each other. The shape of the crack flanks and the relative motion of the flanks are independent of each other. To draw precise conclusions from cracks observed in a construction, a quantitative parameterisation of these cracks is desirable. Often the crack opening width and the opening direction can be assumed to be homogenous at least in sections, defining a unique crack opening vector. Here we present algorithms to automatically characterise cracks by determination of their opening vector based on digital images. The algorithms presented here permit to perform a quantitative and reproducible analysis with weak subsidiary conditions imposed on the photographs. The central parameterisation algorithms are robust against many interfering picture properties and do not depend on the exact position of the crack under consideration within the photograph. The precision of the extracted parameters can be estimated based on a statistical analysis. By using the algorithms for the analysis of true-to-scale rectified images metrical quantities can be obtained. It is possible to integrate the developed applications into the documentation process. The methods can be used together with deformation analysis and other complementary techniques. When working with rectified images the rectification parameters might be transferred automatically between similar pictures; this might be used in the analysis of a temporal sequence of images or to improve detail resolution. The algorithms described here might be used as a basis for assessing the precision of the extracted crack parameters without the need of a statistical analysis. In a more distant perspective, patterns consisting of several cracks might be analysed and the overall relative motion of sections separated by cracks might be deduced, to carry out a combined analysis of several cracks.