Climate and moisture induced stresses in block-glued glulam members of timber bridges

perature and leads to moisture content (MC) variations across the cross section. The MC affects the physical and mechanical properties as well as the dimensions due to shrinkage and swelling below the fibre satura-tion point (FSP). Due to constrained volumetric strains, e.g. due to swelling and shrinkage, changes in moisture content impose moisture induced stresses (MIS) which, if exceeding the tensile strength perpen-dicular to the grain of the material, can cause fractures such as cracks or delaminations. Thus, the correct estimation of the MC is important for the design, quality assurance, and durability of timber bridges. There was the question especially for large glulam members as produced by block-gluing about the impact of ambient climate variations on the moisture induced stresses and possible failure. Block glulam beams form wide cross-sections by gluing single glulam beams to each other. They are used as, e.g., main struc-tural elements for timber bridges, see Figure 1. Therefore, cross sections of practical dimensions were clas-sified regarding the assumed ambient climate in service by numerical simulations that showed the moisture content and gradient over the cross section. Finally, the moisture induced mechanical response was simu-lated using a coupled moisture diffusion and mechanical model. The results were summarized to a practical advice for the dimensioning

Compact Phase Histograms for Guided Exploration of Periodicity

Periodically occurring accumulations of events or measured values are present in many time-dependent datasets and can be of interest for analyses. The frequency of such periodic behavior is often not known in advance, making it difficult to detect and tedious to explore. Automated analysis methods exist, but can be too costly for smooth, interactive analysis. We propose a compact visual representation that reveals periodicity by showing a phase histogram for a given period length that can be used standalone or in combination with other linked visualizations. Our approach supports guided, interactive analyses by suggesting other period lengths to explore, which are ranked based on two quality measures. We further describe how the phase can be mapped to visual representations in other views to reveal periodicity there.Comment: IEEE VIS 2023 Short Pape

Quality assurance of timber structures

The combination of modern architecture with the renewable raw material wood leads to impressive and demanding timber structures with high requirements for planning, production, logistics, commissioning and use. The demands placed on modern wooden structures are constantly increasing in terms of design, appearance, slender cross sections and large spans. Meanwhile, quality assurance during the construction and operational phase is crucial. The realistic estimation of the risks for the timber structure during the construction and operation phase as well as the distribution of wood moisture content in the timber load bearing elements, the risk of cracking and the shape stability of the cross sections are important. The research project focuses on impacts of the local climate, the resulting wood moisture distribution, dimensional stability, moisture induced stresses and possible cracks in the cross-sections. The aim is to provide recommendations for the erection of wooden structures with new research results. The focus lies on the transfer of results from the developed numerical models and methods to secure recommendations for design and planning in practice.The used and developed basics of the project are the climate data of Switzerland, measurements of climate and moisture content in load bearing cross-sections obtained from long-term monitoring campaigns, and the developed numerical model to calculate the moisture diffusion, the dimensional change and the resulting moisture induced stresses. In addition, required material parameters were determined in small laboratory series that improve and support measurements made during the monitoring campaigns. The climatic data and wood moisture content values obtained within the long-term measurement were classified according to the building type and visualized accordingly for the practicing engineers. Published data from other research institutes were also included into the analyses where possible. In addition to the general information on moisture content as listed in the SIA 265:2012, useable climate profiles are now available for a variety of building types and for bridges, too. Specific questions concerning bridges that still led to discussion and unanswered questions were considered and evaluated. The application of a quality assurance monitoring method and system is described. The created numerical model was validated and used in parameter studies to assess the effects of cross-section size or the impact of the construction period. realistic climate profiles found in ice rinks, riding halls and bridges were used to calculate dimensional changes and moisture induced stresses.Recommendations are given on the seasonal fluctuations of humidity and its effects on the timber structures. This could support engineers during the planning and building phase. In addition to the expected fluctuations listed in the SIA 265:2012, obtained results give the planning engineer and authorities new benchmarks for the estimation of the expected wood moisture content within a supporting structure. Of interest could be the distribution across the section width during erection and operation

Monitoring systems for quality assurance of timber bridges

Wood properly protected and controlled is very powerful and durable. Continuous monitoring of wood moisture content is a suitable early warning system. The importance of wood moisture in relation to possible damage in timber construction is shown by the study of [1], where 50 % of all investigated objects show damage or failure due to wood moisture changes or low and high wood moisture contents. Another study by [2] shows that 30% of these objects are damaged due to seasonal or climate-induced wood moisture changes. Since the distribution of wood moisture is often not constant across the cross-section, internal stresses perpendicular to the grain (moisture-induced stresses, MIS) arise due to the anisotropic moisture-strain behaviour. These stresses can easily exceed the characteristic tensile strength perpendicular to the grain and lead to crack development, [3]. In curved glulam beams, these stresses can also lead directly to the total loss of load-bearing capacity, as shown in [4] or [5]

Berücksichtigung des klimatischen Einflusses auf mechanische Verstärkungen

Die aktuellen Entwicklungen im Holzbau werden mit imposanten und leistungsfähigen Objekten, Projekten und Strukturen weltweit beschrieben. Die Leistungsfähigkeit von Holztragelementen kann durch mechanische Verstärkungen, z. B. in Form von eingeklebten Stäben, selbstbohrenden Vollgewindeschrauben oder Gewindestangen, partiell noch erhöht werden. Verstärkungen von Verbindungen oder Tragelementen werden im Holzbau notwendig, wenn die Querschnittsgeometrie eingeschränkt ist oder wenn z. B. gebogene, gekerbte oder durchbrochene Bauteile verwendet werden. Die Wirkungsweise wie auch das statische Trag- und Versagensverhalten von Verstärkungen ist u. a. in Blass et al. (2006, 2010, 2017), Dietsch (2012, 2017) und Trautz & Koj (2008) gezeigt. Zusätzlich zu den statischen Beanspruchungen ergeben sich auch klimatische Beanspruchung aufgrund der Hygroskopie des Holzes und des variierenden Umgebungsklima übers Jahr

Holzbrücken für die nächste Generation von Infrastrukturwegen

Der Werkstoff Holz und seine Vielzahl an Produkten und Technologien können nicht nur für Brücken im Langsamverkehr eingesetzt werden, sondern bieten auch das Potenzial für Schwerlastverkehr. Neu sollen weitspannende Holzbrücken mit einem Hohlkastenquerschnitt und Vorspannung für den Schwerlastverkehr dienen. Für eine klimaneutrale Schweiz 2050 braucht es Antworten aus der Forschung und Entwicklung, um der Baubranche neue, leistungsfähige und klimaneutrale Lösungen aufzuzeigen

Experimental investigation of mesoscale variability of clear spruce mechanical properties in the radial direction

The aim of this work is the investigation of mesoscale/local variability in mechanical properties of clear timber in the radial direction. Clear Norway spruce wood, Picea abies, was used for cutting specimens of different lengths with a small cross-sectional area of 4x4 mm2, in the radial direction of timber boards, and tested under tensile loading. In some boards, specimens were positioned regularly and, in some others, randomly, and local deformations in each specimen were measured during the tests. The results indicate a significant variability in the specimens’ elastic moduli and strengths. A correlation between the mesostructure of clear timber and mesoscale/local variability of the transverse elastic modulus in the specimens was observed. Specimens’ failures were classified and a reasonable correlation with the corresponding strength values was observed

The effects of a single bout of exercise on motor memory interference in the trained and untrained hemisphere

Increasing evidence suggests that cardiovascular exercise has positive effects on motor memory consolidation. In this study, we investigated whether a single session of high-intensity interval training (HIIT) mitigates the effects of practicing an interfering motor task. Furthermore, learning and interference effects were assessed in the actively trained and untrained limb as it is known that unilateral motor learning can cause bilateral adaptations.Subjects performed a ballistic training and then the HIIT either before (HIIT_before) or after (HIIT_after) practicing an interfering accuracy task (AT). The control group (No_HIIT) did not participate in the HIIT but rested instead. Performance in the ballistic task (BT) was tested before and after the ballistic training, after the exercise and practice of the AT and 24 h later. After ballistic training, all groups showed comparable increases in performance in the trained and untrained limb. Despite the practice of the AT, HIIT_before maintained their BT performance after the high-intensity interval training whereas HIIT_after (trend) & No_HIIT showed prominent interference effects. After 24 h, HIIT_before still did not show any interference effects but further improved ballistic motor performance. HIIT_after counteracted the interference resulting in a comparable BT performance after 24 h than directly after the ballistic training while No_HIIT had a significantly lower BT performance in the retention test. The results were similar in the trained and untrained limb. The current results imply that a single session of cardiovascular exercise can prevent motor interference in the trained and untrained hemisphere. Overall learning was best, and interference least, when HIIT was performed before the interfering motor task

Desmosomal Molecules In and Out of Adhering Junctions: Normal and Diseased States of Epidermal, Cardiac and Mesenchymally Derived Cells

Current cell biology textbooks mention only two kinds of cell-to-cell adhering junctions coated with the cytoplasmic plaques: the desmosomes (maculae adhaerentes), anchoring intermediate-sized filaments (IFs), and the actin microfilament-anchoring adherens junctions (AJs), including both punctate (puncta adhaerentia) and elongate (fasciae adhaerentes) structures. In addition, however, a series of other junction types has been identified and characterized which contain desmosomal molecules but do not fit the definition of desmosomes. Of these special cell-cell junctions containing desmosomal glycoproteins or proteins we review the composite junctions (areae compositae) connecting the cardiomyocytes of mature mammalian hearts and their importance in relation to human arrhythmogenic cardiomyopathies. We also emphasize the various plakophilin-2-positive plaques in AJs (coniunctiones adhaerentes) connecting proliferatively active mesenchymally-derived cells, including interstitial cells of the heart and several soft tissue tumor cell types. Moreover, desmoplakin has also been recognized as a constituent of the plaques of the complexus adhaerentes connecting certain lymphatic endothelial cells. Finally, we emphasize the occurrence of the desmosomal transmembrane glycoprotein, desmoglein Dsg2, out of the context of any junction as dispersed cell surface molecules in certain types of melanoma cells and melanocytes. This broadening of our knowledge on the diversity of AJ structures indicates that it may still be too premature to close the textbook chapters on cell-cell junctions

Off-grid: solar powered LED illumination impacts epigeal arthropods

Advances in LED technology combined with solar, storable energy bring light to places remote from electricity grids. Worldwide more than 1.3 billion of people are living off-grid, often in developing regions of high insect biodiversity. In developed countries, dark refuges for wildlife are threatened by ornamental garden lights. Solar powered LEDs (SPLEDs) are cheaply available, dim, and often used to illuminate foot paths, but little is known on their effects on ground living (epigeal) arthropods. We used off-the-shelf garden lamps with a single ‘white’ LED (colour temperature 7250 K) to experimentally investigate effects on attraction and nocturnal activity of ground beetles (Carabidae). We found two disparate and species-specific effects of SPLEDs. (i) Some nocturnal, phototactic species were not reducing activity under illumination and were strongly attracted to lamps (>20-fold increase in captures compared to dark controls). Such species aggregate in lit areas and SPLEDs may become ecological traps, while the species is drawn from nearby, unlit assemblages. (ii) Other nocturnal species were reducing mobility and activity under illumination without being attracted to light, which may cause fitness reduction in lit areas. Both reactions offer mechanistic explanations on how outdoor illumination can change population densities of specific predatory arthropods, which may have cascading effects on epigeal arthropod assemblages. The technology may thus increase the area of artificial light at night (ALAN) impacting insect biodiversity. Measures are needed to mitigate effects, such as adjustment of light colour temperature and automated switch-offs