SENSOR EVALUATION FOR CRACK DETECTION IN CONCRETE BRIDGES Merkle, D.; Schmitt, A.; Reiterer, A.
International archives of the photogrammetry, remote sensing and spatial information sciences.,
08/2020, Letnik:
XLIII-B2-2020
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Bridges are one of the most critical traffic infrastructure objects, therefore it is necessary to monitor them at regular intervals. Nowadays, this monitoring is made manually by visual inspection. ...In recent projects, the authors are developing automated crack detection systems to support the inspector. In this pre-study, different sensors, like different camera systems for photogrammetry, a laser scanner, and a laser triangulation system are evaluated for crack detection based on a defined required minimum crack width of 0.2 mm. The used test object is a blasted concrete plate, sized 70 cm × 70 cm × 5 cm and placed in an outdoor environment. The results of the data acquisition with the different sensors are point clouds, which make the results comparable. The point cloud from the chosen laser scanner is not sufficient for the required crack width even at a low speed of 1 m/s. The RGB or intensity information of the photogrammetric point clouds, even based on a low-cost smartphone camera, contain the targeted cracks. The authors advise against using only the 3D information of the photogrammetric point clouds for crack detection due to noise. The laser triangulation system delivers the best results in both intensity and 3D information. The low weight of camera systems makes photogrammetry to the preferred method for an unmanned aerial vehicle (UAV). In the future, the authors aim for crack detection based on the 2D images, automated by using machine learning, and crack localisation by using structure from motion (SfM) or a positioning system.
The study demonstrates the successful application of vancomycin for inhibiting growth of the contaminant
Bacillus cereus in a polyhydroxyalkanoate (PHA) production process with
Hydrogenophaga ...pseudoflava on whey. The minimum inhibiting concentration (MIC) of vancomycin for both strains was calculated in minimal medium H3 as well as in H3 medium supplemented with yeast extract. MIC for
B. cereus was 0.57 μg mL
−1 and 1.63 μg mL
−1 in H3 and H3 plus yeast extract respectively. For
H. pseudoflava, MIC amounted to 2.8 μg mL
−1 in H3 medium and 6.88 μg mL
−1 in H3 plus yeast extract. The effect of vancomycin on PHA production was minimal or negligible up to a vancomycin concentration of 1 μg mL
−1 in both media. The specific PHA production rates of
H. pseudoflava decreased with increasing antibiotics in a minimal medium but in media supplemented with yeast extract the specific PHB production rates increased as the antibiotics concentrations increased.
Position-resolved small-angle X-ray scattering was used to investigate the nanostructure of the wood cell wall in two softwood species (Norwegian spruce and Scots pine) and two hardwood species ...(pedunculate oak and copper beech). The tilt angle of the cellulose fibrils in the wood cell wall versus the longitudinal cell axis (microfibril angle) was systematically studied over a wide range of annual rings in each tree. The measured angles were correlated with the distance from the pith and the results were compared. The microfibril angle was found to decrease from pith to bark in all four trees, but was generally higher in the softwood than in the hardwood. In Norwegian spruce, the microfibril angles were higher in late wood than in early wood; in Scots pine the opposite was observed. In pedunculate oak and copper beech, low angles were found in the major part of the stem, except for the very first annual rings in pedunculate oak. The results are interpreted in terms of mechanical optimization. An attempt was made to give a quantitative estimation for the mechanical constraints imposed on a tree of given dimensions and to establish a model that could explain the general decrease of microfibril angles from pith to bark.
Mode I fracture characteristics of different wood species (one softwood and three hardwoods) in two crack propagation systems were investigated using the wedge splitting test under loading ...perpendicular to the grain. From the obtained load–displacement curves the initial slope, the critical stress intensity factor and the specific fracture energy were determined. The initial slope and the critical stress intensity factor were shown to depend strongly on density within all species whereas for the specific fracture energy differences between the softwood and the hardwoods were found. Differences between the crack propagation systems could be explained by the higher volume fraction of radial oriented tissue (rays) of the hardwoods.
The moisture content is known to influence the properties of wood. While mechanical parameters like stiffness and strength decrease with increasing moisture content, investigations on the influence ...on fracture properties have been concentrated on linear elastic fracture mechanics. In this paper, the wedge splitting method is used to investigate also the non-linear fracture behaviour of sprucewood at different moisture contents. Complete load-displacement curves at four different moisture levels are evaluated. While the initial slope and the maximum stress state are decreasing with increasing moisture content the specific fracture energy is increasing. It is shown that this behaviour can be attributed to an increase in ductility which increases both the dissipated energy during crack initiation and the one in the crack propagation phase.
Spruce and beech wood specimens were sanded with four different grain sizes. Surface morphological and chemical changes were determined by roughness measurement, surface free energy determination ...according to acid-base theory and X-ray photoelectron spectroscopy. An analysis model was proposed to describe chemical changes due to sanding and the data were analysed according to it. It could be shown that spruce and beech behave similarly over a wide range and that chemical changes are non-linear functions of grain size and thus surface roughness. A maximum of surface free energy and a maximum of carbon C1s sub-peak ratio (ratio of carbon bonded to a single non-carbonyl oxygen to carbon bonded only to hydrogen or other carbon atoms) was found for middle grain size.
X-ray photoelectron spectroscopy (XPS) was used to characterize the surfaces of mechanically treated wood. Microtomed and sanded surfaces of spruce, larch, beech and oak were investigated. Changes ...due to the sanding process were identified from the survey spectra as well as from the detailed C1s spectra. The changes were quantified with the atomic ratio of oxygen to carbon and with a detailed analysis of the contributions to the C1s peak. The identified changes were explained in terms of the macromolecular wood substances and in terms of density and the amount of extractives.
Wood is a natural fibre composite with a hierarchical cellular structure of a specific strength and a specific modulus of elasticity that can be compared with those of other common construction ...materials. Each wood cell is typically built of cellulose fibrils spiralling around the macroscopic fibre direction. While it is natural to assume a relation between the microfibril angle (MFA) and the mechanical properties, a good correlation has up to now only been established for single fibres, where a larger extensibility was found for fibres with larger MFA. In the present paper, we show for the first time that this relation even exists for thin (200 μm) sections of wood, which provides strong evidence for the fact that the MFA optimizes the extensibility of wood. In a combination of tensile tests with structural investigations by small angle X-ray scattering on the same sample of Picea abies, we found a remarkable increase in maximum strain with increasing MFA, and also a change in the elastic moduli.
The nanostructure of the wood cell wall and, in particular the tilt angle of the cellulose fibrils versus the longitudinal cell axis (microfibril angle, MFA), are known to play a key role in ...determining the mechanical properties of wood. A variation of microfibril angles during growth may therefore be regarded as a means to adapt to different loading situations. In the present study, a branch of Norway spruce (Picea abies) was used as a model system. The change of microfibril angles with increasing age and size of the branch and therefore increasing gravitational load was systematically investigated. Small angle X-ray scattering (SAXS) was applied to obtain a map of MFA all over the branch as a function of the distance from the trunk within each annual ring. It was found that in compression wood the MFA decreased continuously from the trunk towards the tip in all annual rings. In opposite wood, however, the course of microfibril angles was found to change considerably with the age of the branch: in the outer annual rings, very small microfibril angles occurred in the middle part of the branch. The results are discussed in view of the mechanical implications of different microfibril angles.
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