Digitale Photogrammetrie in der Bautechnik

Abstract

Die digitale Nahbereichsphotogrammetrie ermöglicht die berührungslose Erfassung von Verformungen, Rissen und anderen Schädigungen bei experimentellen Untersuchungen von Baustoffen, Bauteilen und Baukonstruktionen. Bei Beton bzw. Stahlbeton sind die zu beobachtenden Dehnungen (ca. 3, 5 ‰ Druckbruchdehnung, ca. 0,1 ‰ Zugbruchdehnung) und Rissbreiten (ab 0,05 mm) im Vergleich zu anderen Materialien sehr klein. Bei Betonbauteilen wird die digitale Nahbereichsphotogrammetrie daher oft an der Leistungsgrenze betrieben. Dann entscheidet die optimale Wahl maßgebender Systemparameter darüber, ob die Messaufgabe mit hinreichender Genauigkeit durchgeführt werden kann. In einer systematischen Studie zu maßgebenden Systemparametern wurden Einflussgrößen und Abhängigkeiten mit einer üblichen Photogrammetrieanlage untersucht. Zu den untersuchten Systemparametern zählen Parameter der Bildaufnahme – wie Signalisierung, Beleuchtung, Belichtung, Bildrate, Objektposition – und Parameter der Bildauswertung – wie Größe, Anzahl und Position der Facetten. Wesentliche Ergebnisse werden vorgestellt und diskutiert. Daraus werden Empfehlungen für Systemparameter beim praktischen Einsatz, erreichbare Messgenauigkeit und Hinweise zu Anwendungsgrenzen abgeleitet. Digital photogrammetry in construction engineering – Influence of major system parameters and accuracy potential in applications Digital close range photogrammetry enables non‐contact acquisition of deformations, cracks and other damages from materials, members and building constructions. Strains of concrete and reinforced concrete (ca. 3,5 ‰ ultimate compression strain, ca. 0,1 ‰ ultimate tension strain) and crack widths (from 0,05 mm) are very small compared to other materials. Thus, digital close range photogrammetry often operates on its limits when being applied to concrete structures. The optimal choice of major system parameters decides whether measurements can be accomplished with sufficient accuracy. In a systematic study of relevant system parameters influences and interdependencies were investigated by means of conventional digital photogrammetry equipment. System parameters studied include both the image acquisition process – such as signaling, lighting, exposure, frame rate, object location – and the image analysis parameters – such as size, number and position of facets. Key results are presented and discussed. Finally, recommendations are derived for system parameters in practical application and application limits.

Digital image correlation strain measurement of ultra‐high‐performance concrete‐prisms under static and cyclic bending‐tensile stress

“…In addition, the measurement accuracy must also be taken into account for the comparison of both measurement methods. The accuracy of DIC measurements is described by the SD of the measured values . This is calculated by the deviation Δ ε of the measured values from the mean value curve (Figure ).…”

“…The cyclic tests were performed load‐controlled on five different test series (n° VC1, VC2, VC3, VC4, and VC5) with the same lower‐ and upper stress‐level but different loading rates as specified in Table . This procedure was chosen because the measurement noise of the DIC depends on the measuring rate, which has to be selected according to the loading rate . Measurement noise is a fluctuation of the results underlying any measurement system and defines the accuracy of the system.…”

Crack Analysis of Textile Reinforced Concrete Using Automated Crack Evaluation via Digital Image Correlation

“…In addition to the crack analysis, parameters such as pattern visibility, lighting effects, aperture, number of cameras, exposure time and exposure type affect the crack evaluation [3,11,22,23]. To quantify the impact of camera resolution on mechanical properties and multiple crack characteristics using DIC, Godek et al [16] conducted experiments on cementitious composites.…”

“…This research demonstrated that increased resolution results in finer pattern precision and led to a twofold increase in the number of detected cracks during the analysis. During the evaluation process of measurements using DIC, key parameters for evaluation include facet size, the quantity of images per measurement, the spacing between two facets (facet overlap), strain tensors' neighborhood, averaging spatially and temporally, and the threshold for the scaling factor based on the major strain [3,22]. However, it should be noted that the accuracy of image analysis is constrained by systematic and random errors.…”

“…Systematic errors may arise from deficiencies in the mathematical model or mechanical instabilities in the camera setup, such as temperature-induced deformation or mechanical instabilities. On the other hand, random errors can result from factors like image noise, rounding errors in floating point calculations, mechanical instabilities, and over-determination errors in the multi-camera setups [22].…”