Rotational Stiffness of Timber-to-Timber Connections with Self-Tapping axially loaded Screws

Self-tapping axially loaded screws provide high load-carrying capacity and great stiffness. Due to these advantages, they were preferably applied to realise connections for tension members. While the translational stiffness of those connections can be estimated for engineering purposes sufficiently, knowledge about the rotational stiffness is still low. The investigations reported here show the influence of the inclination and the geometrical arrangement of the self-tapping screws on the rotational stiffness of connections for tension members. A test set-up was therefore developed. It enables that tensile forces and rotation are simultaneously effective and quantitatively independently of each other. The experimental results show that the inclination of the screws and the resulting compressive stress in the shear plane has a major influence on the rotational stiffness and that the stiffness of the screws themselves becomes less effective

A validation method for computationally determined strength values

The article presents a validation method for computationally determined glulam strength values. Using numerically modelled glulam, featuring brittle tensile failure, different load configurations were examined in a computationally performed study. The corresponding bending tests show variations in the bending strength depending on the applied configuration. From physical perspective, these strength variations are caused by the interaction between the actual natural strength variability, changes in the load configuration and/or the member volume and the brittle material behaviour. A targeted comparison between the apparent strength variations, obtained from the computational procedure on the one hand and a related analytical method on the other hand, leads to almost identical results. The comparison proves therefore that the computational approach reflects the principles of the size effect according to the Weibull theory with sufficient accuracy. The study generally exemplifies that related analytical methods, if available, are a beneficial tool to verify and validate computational procedures

Computergestützte Verfahren zur pragmatischen Beurteilung der Tragwiderstände von Brettschichtholz: Zusammenfassung exemplarischer Simulationsstudien

In diesem Buch werden Erfahrungen und Ergebnisse aus Computersimulationen in der Disziplin der Brettschichtholzforschung dargestellt. Zum methodischen Vorgehen enthält es Verweise auf Vorarbeiten, die den Zugang zu elementaren Grundlagen erleichtern, sowie konstruktive und kritische Erläuterungen zur Brettschichtholzmodellierung und Simulation von Biege-, Zug- und Druckversuchen. Abschließend wird diskutiert, welche Relevanz die gewonnenen Simulationsergebnisse in baupraktischer Hinsicht haben

Tensile Stiffness of Laminated Segment Timber

Laminated Segment Timber (LST) is an engineered wood product. It is panelshaped and glued of trapezoidal spruce lamellas. As intermediate product, it is provided for the processing to layered LST, a glulam-like building material. The source material for LST are mechanically graded logs. This study aims at developing modelling and simulation techniques to assess the mechanical properties of LST. It is reported about 294 nondestructive tensile tests on specimens from LST and about the corresponding results. Digital image correlation was used to examine the tensile stiffness. Both global and local stiffness of the LST specimens were analysed in terms of tensile MOE. It was found that the local MOE of modelling units for LST can be predicted by the dynamic MOE of the source material and a newly developed knot ratio referring to the cross-section of LST specimens. Using this correlation, two stiffness models were derived for the local MOE. Their response shows good agreement with that of reference models from the literature. The models are, therefore, suitable for incorporation into a layered LST finite element model which is intended for predicting the mechanical properties

Aortic aneurysm and aortic graft infection related to Mycobacterium bovis after intravesical Bacille Calmette–Guérin therapy—a case series

Background: So called "mycotic" aortic aneurysms account for only 0.7 to 1.3% of all aortic aneurysms and are commonly caused by Staphylococcus aureus and Salmonella species. Bacillus Calmette-Guerin (BCG), a live attenuated strain of Mycobacterium bovis, is part of the therapy of non-muscle-invasive bladder cancer (NMIBC). Case presentation: We report a case series of three patients with a mycobacterial graft infection related to BCG after surgical treatment of a presumed mycotic aortic aneurysm as an extremely rare complication after NMIBC treatment. All three patients developed aortic aneurysm after BCG instillation and subsequent mycobacterial graft infection. Conclusion: Diagnosis requires a high degree of suspicion because of its nonspecific symptoms and imaging. The pathogen is not detected by standard microbiological testing. Treatment includes triple antimycobacterial therapy and radical surgical interventions. Graft preservation may be considered if no anastomosis is involved

Schadensanalyse von Hallentragwerken aus Holz

Diese Forschungsarbeit, ausgelöst durch Einstürze von Hallen aus Holz im Winter 2006, möchte Schadensfälle und begleitenden Umstände nicht individuell, sondern gemeinsam darstellen und ganzheitlich analysieren. Es werden Schwachpunkte, fehleranfällige Konstruktionen und Ursache-Wirkung-Mechanismen aufgezeigt und Konsequenzen benannt

Characteristic bending strength of beech glulam

This project was carried out to derive the characteristic bending strength of beech glulam. 47 full size glulam beams with combined symmetrical lay-up were produced. For this purpose mechanical grading was used to classify the lamellae according to the dynamic MOE. The beams were tested according to EN 408. The bending strength exceeds 44.5 N/mm2. The structural properties of beech boards were determined as input for a finite-element-based computer model. It was specifically developed to predict the bending strength of beech glulam. Comparisons between the experimental data and the analytical results from the computer model show a good agreement. Depending on the bending strength of finger joints and the tensile strength of boards design proposals were numerically derived taking into account visual and/or mechanical grading