Querkrafttragverhalten von Stahlbeton-Fahrbahnplatten

Die vorliegende Arbeit beschäftigt sich mit dem Tragverhalten von Stahlbeton-Fahrbahnplatten. Der Schwerpunkt liegt auf dem Lastabtrag von konzentrierten Einzel- bzw. Blocklasten, wie sie bei Brückenbauwerken in Form von Radlasten auftreten. Die gewonnenen Erkenntnisse können aber auch ohne weiteres auf allgemeine Fälle von konzentrierten Blocklasten auf Stahlbetonplatten übertragen werden. Im Zuge der bisherigen Forschungstätigkeit zur Querkrafttragfähigkeit von Stahlbeton-Fahrbahnplatten konnte wiederholt festgestellt werden, dass die Querkrafttragfähigkeit der Platten unter Einzellasten höher ist, als der rechnerischeWiderstand nach aktuellen Bemessungsregeln erwarten lässt. Trotzdem konnte bisher kein erhöhter Tragwiderstand abgeleitet werden. Diese Diskrepanz soll durch die vorliegende Arbeit behoben werden. Nach einem Überblick über den Stand des Forschungsgebietes werden zunächst der Forschungsbedarf und offene Fragestellungen abgeleitet. Anhand von eigenen Großmodellversuchen an der Technischen Universität Hamburg (TUHH) kann direkt eine Vielzahl dieser offenen Fragen aus den vorhergehenden Forschungsarbeiten beantwortet werden. Unter anderem kann der Einfluss des direkten Lastabtrags von Einzellasten bei Platten quantifiziert werden. Ergänzend werden Material-nichtlineare FE-Simulationen durchgeführt, um den Lastabtrag der Platten vertieft zu erforschen. Die Berechnungen werden mit realen Messwerten validiert. Es lässt sich zeigen, dass der übliche ortsfeste Schnitt im Auflagerbereich zur Bestimmung der Beanspruchung von Platten unter Einzellasten nicht sinnvoll ist. Der Ort des Versagens liegt im Bereich der Lasteinleitung der Einzellasten. Hier sollten auch die maßgebenden Querkräfte bestimmt werden. Diese sind aber um ein Vielfaches höher als die Querkräfte am Auflager der Platte. Ein praxisnahes Vorgehen zur Ermittlung der Beanspruchung aus konzentrierten Einzellasten aus linear-elastischen FE-Berechnungen wird gezeigt und ein Ansatz zur Berücksichtigung der erhöhten Tragfähigkeit für Stahlbetonplattentragwerke auf Grundlage der aktuellen Bemessungsgleichung nach EC2 vorgeschlagen. Es ergibt sich eine mögliche Steigerung der rechnerischen Querkrafttragfähigkeit für Plattentragwerke um ca. 50 %. Das erforderliche Sicherheitsniveau bei diesem modifizierten Nachweis der Querkrafttragfähigkeit wird mit Hilfe einer statistischen Datenbankanalyse von ausgewählten Plattenversuchen nachgewiesen. Es wird erläutert, wie der direkte Lastabtrag von auflagernahen konzentrierten Lasten phänomenologisch funktioniert und wie der Versagensmechanismus der Platten unter Einzellasten mit dem Durchstanzen zusammenhängt. Abschließend kann aus den gewonnen neuen Erkenntnissen abgeleitet werden, wie der Anteil der geneigten Druckstrebe aus Biegung Vccd bei gevouteten Platten beurteilt werden sollte.The present work deals with the load-bearing behavior of reinforced concrete slabs. The focus is on the load transfer of concentrated single or block loads, as they occur in bridge structures in the form of wheel loads. However, the findings can also easily be applied to general cases of concentrated block loads on reinforced concrete slabs. In the previous research work on the bearing capacity in shear of reinforced concrete roadway slabs it could be repeatedly stated that the shear bearing capacity of the slabs under single loads is higher than the calculated resistance according to current design rules would expect. Nevertheless, so far no increased bearing capacity could be derived. This discrepancy should be remedied by the present work. After an overview of the field of research and previously performed test series, the research needs and open questions are derived. Based on this, the structural behavior of reinforced concrete slabs under single loads is examined on the basis of large-scale model tests performed at TUHH. From this, one can directly answer many open questions from previous research. In addition, material-non-linear FE simulations are performed to investigate the load transfer of the plates in more detail. The calculations are validated based on the real experiments. It can be shown that the usual fixed relevant design section at the support region is not meaningful, and that the shear forces should be determined close to the concentrated loads. However, these are many times higher than the shear forces at the support of the slab. A hands-on approach to determining the internal forces out of concentrated loads from linearelastic FE calculations is presented and an approach to taking into account the increased load bearing capacity of reinforced concrete slab structures based on the current design equation according to EC2 is proposed. In doing so, the required level of safety in the case of modified proof of the shear bearing capacity is demonstrated by means of a statistical database analysis of selected tests on slabs. It is explained how the direct load transfer of concentrated loads close to the support works phenomenological, and how the failure mechanism of slabs under single loads is related to punching. Finally, it will be shown how the fraction of the inclined compression strut from bending Vccd should be evaluated on haunched slabs

Versuche zur Querkrafttragfähigkeit von Stahlbetonplatten unter auflagernahen Einzellasten : Versuchsbericht

Versuchsbericht zu einer Versuchsreihe zur Querkrafttragfähigkeit und zum Lastabtrag von Stahlbetonplatten ohne Querkraftbewehrung unter konzentrierten Blocklasten.Test report on a series of tests on the shear capacity and load transfer of reinforced concrete slabs without shear reinforcement under concentrated block loads

Unfractionated and Low Molecular Weight Heparin Reduce Platelet Induced Epithelial-Mesenchymal Transition in Pancreatic and Prostate Cancer Cells

The interaction with platelets is of crucial importance for tumor cells passing through hematogenous metastasis. Platelets protect cancer cells from immune surveillance and exhibit many other prometastatic effects. Notably, platelets can change the epithelial tumor phenotype, a process termed epithelial-mesenchymal transition (EMT), which confers stem cell-like properties onto tumor cells associated with an increased motility and drug resistance. The aim of the study is to investigate the impact of heparin on the platelet induced EMT program in pancreatic and prostate tumor cells. Platelet activation and interaction with cancer cells were determined by static adhesion assays. Applying ELISAs, the platelet release of EMT inducing mediators was quantified. EMT marker protein expression by tumor cells was explored by western blot and qPCR. Our data show that different tumor cell entities have different platelet binding capacities and also that a weak interaction is sufficient to change tumor cell phenotype. Additionally, unfractionated heparin (UFH) as well as low molecular weight heparin (LMWH) reduced tumor cell platelet interaction. Subsequently, attenuated platelet-derived mediator release resulted in reduced EMT marker protein and transcription factor expression by the cancer cells and decreased cell migration. These data suggest that heparin reduces platelet induced EMT program and prevents the formation of cancer cells with stem cell-like properties. This additional mechanism argues for the use of heparin in oncological applications

Evaluation of viscosities of typical drainage fluids to promote more evidence-based catheter size selection

Abstract Percutaneous drainage is a first-line therapy for abscesses and other fluid collections. However, experimental data on the viscosity of body fluids are scarce. This study analyses the apparent viscosity of serous, purulent and biliary fluids to provide reference data for the evaluation of drainage catheters. Serous, purulent and biliary fluid samples were collected during routine drainage procedures. In a first setup, the apparent kinematic viscosity of 50 fluid samples was measured using an Ubbelohde viscometer. In a second setup, the apparent dynamic viscosity of 20 fluid samples obtained during CT-guided percutaneous drainage was measured using an in-house designed capillary extrusion experiment. The median apparent kinematic viscosity was 0.96 mm2/s (IQR 0.90–1.15 mm2/s) for serous samples, 0.98 mm2/s (IQR 0.97–0.99 mm2/s) for purulent samples and 2.77 mm2/s (IQR 1.75–3.70 mm2/s) for biliary samples. The median apparent dynamic viscosity was 1.63 mPa*s (IQR 1.27–2.09 mPa*s) for serous samples, 2.45 mPa*s (IQR 1.69–3.22 mPa*s) for purulent samples and 3.50 mPa*s (IQR 2.81–3.90 mPa*s) for biliary samples (all differences p < 0.01). Relative to water, dynamic viscosities were increased by a factor of 1.36 for serous fluids, 2.26 for purulent fluids, and 4.03 for biliary fluids. Serous fluids have apparent viscosities similar to water, but biliary and purulent fluids are more viscous. These data can be used as a reference when selecting the drainage catheter size, with 8F catheters being appropriate for most percutaneous drainage cases

Role of van der Waals interaction in forming molecule-metal junctions: flat organic molecules on the Au(111) surface

The self-assembly of flat organic molecules on metal surfaces is controlled, apart from the kinetic factors, by the interplay between the molecule-molecule and molecule-surface interactions. These are typically calculated using standard density functional theory within the generalized gradient approximation, which significantly underestimates nonlocal correlations, i.e. van der Waals (vdW) contributions, and thus affects interactions between molecules and the metal surface in the junction. In this paper we address this question systematically for the Au(111) surface and a number of popular flat organic molecules which form directional hydrogen bonds with each other. This is done using the recently developed first-principles vdW-DF method which takes into account the nonlocal nature of electron correlation [M. Dion et al., Phys. Rev. Lett. 2004, 92, 246401]. We report here a systematic study of such systems involving completely self-consistent vdW-DF calculations with full geometry relaxation. We find that the hydrogen bonding between the molecules is only insignificantly affected by the vdW contribution, both in the gas phase and on the gold surface. However, the adsorption energies of these molecules on the surface increase dramatically as compared with the ordinary density functional (within the generalized gradient approximation, GGA) calculations, in agreement with available experimental data and previous calculations performed within approximate or semiempirical models, and this is entirely due to the vdW contribution which provides the main binding mechanism. We also stress the importance of self-consistency in calculating the binding energy by the vdW-DF method since the results of non-self-consistent calculations in some cases may be off by up to 20%. Our calculations still support the usually made assumption of the molecule-surface interaction changing little laterally suggesting that single molecules and their small clusters should be quite mobile at room temperature on the surface. These findings support a gas-phase modeling for some flat metal surfaces, such as Au(111), and flat molecules, at least as a first approximation