02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
Browse
17 results
Search Results
Item Open Access Buckling resistance of longitudinally stiffened panels with closed stiffeners under direct longitudinal stresses(2022) Pourostad, Vahid; Kuhlmann, UlrikeThe buckling behaviour of panels may be determined according to EN 1993‐1‐5 [1]. Most of the design rules relating to stiffened panels in EN 1993‐1‐5 were derived on the basis of open‐section stiffeners. Several recent investigations have shown that the application of the design rules according to EN 1993‐1‐5 considering the torsional stiffness of the stiffeners may overestimate the resistance of the panels. Therefore, the recent Amendment A2 to EN 1993‐1‐5 states that the torsional stiffness of stiffeners should generally be neglected in determining critical plate buckling stresses. In addition, prEN 1993‐1‐5 [2] provides rules for considering the torsional stiffness of stiffeners. However, in this article it is shown that even the rules of prEN 1993‐1‐5 are not sufficient to overcome the safety deficiencies. The article focuses on the investigation of the buckling behaviour of stiffened panels with closed‐section stiffeners subjected to constant longitudinal compression stresses. Improved rules have been developed that allow to consider the torsional stiffness of the stiffeners. Based on an extensive numerical parametric study, a new interpolation equation between column‐ and plate‐like behaviour is proposed. In comparison to [3], the investigations have been extended to the effective width method. They show that the proposal provides a safe and economic solution for the reduced stress method and the effective width method when considering the torsional stiffness of stiffeners by calculating the critical plate buckling stresses.Item Open Access Numerical and experimental investigation on concrete splitting failure of anchor channels(2021) Bogdanić, Anton; Casucci, Daniele; Ožbolt, JoškoConcrete splitting failure due to tension load can occur when fastening systems are located close to an edge or corner of a concrete member, especially in thin members. This failure mode has not been extensively investigated for anchor channels. Given the current trend in the construction industry towards more slender concrete members, this failure mode will become more and more relevant. In addition, significantly different design rules in the United States and Europe indicate the need for harmonization between codes. Therefore, an extensive numerical parametric study was carried out to evaluate the influence of member thickness, edge distance, and anchor spacing on the capacity of anchor channels in uncracked and unreinforced concrete members. One of the main findings was that the characteristic edge distance depends on the member thickness and can be larger than 3hef (hef = embedment depth) for thin members. Based on the numerical and experimental test results, modifications of the design recommendations for the splitting failure mode are proposed. Overall, the authors recommend performing the splitting verification separately from the concrete breakout to design anchor channels in thin members more accurately.Item Open Access Numerical and experimental investigation of anchor channels subjected to tension load in composite slabs with profiled steel decking(2022) Bogdanić, Anton; Casucci, Daniele; Ožbolt, JoškoIn curtain wall applications, anchor channels are frequently installed near the edge of composite slabs with profiled steel decking. The complex concrete geometry of these floor slabs affects the capacity of all concrete failure modes, but there are currently no guidelines or investigations available on this topic. The main objective of the present research is to investigate how the position of anchor channels and the complex slab geometry influence the tensile capacity of anchor channels. For this purpose, an extensive numerical parametric study was performed using the 3D nonlinear FE code MASA, which is based on the microplane constitutive model. In order to validate the numerical results, an experimental program was carried out for some of the configurations possible in practice. Based on the results, recommendations are given for the reduction in the tensile capacity of anchor channels in composite slabs with profiled steel decking.Item Open Access Particulate matter versus airborne viruses : distinctive differences between filtering and inactivating air cleaning technologies(2022) Burdack-Freitag, Andrea; Buschhaus, Michael; Grün, Gunnar; Hofbauer, Wolfgang Karl; Johann, Sabine; Nagele-Renzl, Anna Maria; Schmohl, Andreas; Scherer, Christian RudolfThe current pandemic of the SARS-CoV-2 virus requires measures to reduce the risk of infection. In addition to the usual hygiene measures, air cleaners are a recommended solution to decrease the viral load in rooms. Suitable technologies range from pure filters to inactivating units, such as cold plasma or UVC irradiation. Such inactivating air cleaners, partly combined with filter technology, are available on the market in various designs, dimensions and technical specifications. Since it is not always clear whether they may produce undesirable by-products, and the suitability for particular applications cannot be assessed on the basis of the principle of operation, the effectivity of six inactivating devices was investigated in a near-real environment. The investigations were based on a standard method published by the VDI. The procedure was extended in such a way that a permanent virus source was simulated, which corresponds to the presence of a person suffering from COVID-19 in a room. The study addresses the difference of the mere presence of viruses to the determination of the virulence. As a result, a deep understanding is provided between the behavior of a virus as a pure aerosolized particle and its real infectivity in order to enable the assessment of suitable air cleaners.Item Open Access Simulation-based investigations of the load-bearing behavior of concrete hollow sphere slabs exposed to fire(2022) Miller, Olga; Gericke, Oliver; Nigl, David; Kovaleva, Daria; Blandini, LucioThis paper concerns the investigations of the flexural capacity of concrete slabs with integrated concrete hollow spheres that are subjected to fire and their mass saving potential compared to solid slabs. (1) Background: The overuse of concrete in construction contributes considerably to global CO2 emissions; therefore, the potential for mass reduction in structural components must be fully exploited. However, the design regulations for weight-minimized components, particularly slabs with internal voids, are often not explicitly covered by standards, such as the fire design standard relevant to this paper. (2) Methods: Based on the design guidelines for statically determinate structures in Eurocode 2-2 and DIN 4102-4, a solid slab and a concrete slab with concrete hollow spheres are designed and evaluated with regard to their weight and flexural capacity when subjected to fire. The temperature profiles within the slab cross-section exposed to fire are simulated using ABAQUS finite element software, considering the physically nonlinear, temperature-dependent material behavior of concrete and steel. Using these results, the strain distribution corresponding to the maximum flexural moment is iteratively determined at the weakest cross-section, which exhibits the largest void. (3) Results: All components show sufficient flexural capacity for the target fire duration of 90 min. (4) Conclusion: In the context of this study, the design guidelines according to Eurocode 2-2 and DIN 4102-4 are proven to be fully applicable also for concrete hollow sphere slabs.Item Open Access Data-driven prediction and uncertainty quantification of process parameters for directed energy deposition(2023) Hermann, Florian; Michalowski, Andreas; Brünnette, Tim; Reimann, Peter; Vogt, Sabrina; Graf, ThomasLaser-based directed energy deposition using metal powder (DED-LB/M) offers great potential for a flexible production mainly defined by software. To exploit this potential, knowledge of the process parameters required to achieve a specific track geometry is essential. Existing analytical, numerical, and machine-learning approaches, however, are not yet able to predict the process parameters in a satisfactory way. A trial-&-error approach is therefore usually applied to find the best process parameters. This paper presents a novel user-centric decision-making workflow, in which several combinations of process parameters that are most likely to yield the desired track geometry are proposed to the user. For this purpose, a Gaussian Process Regression (GPR) model, which has the advantage of including uncertainty quantification (UQ), was trained with experimental data to predict the geometry of single DED tracks based on the process parameters. The inherent UQ of the GPR together with the expert knowledge of the user can subsequently be leveraged for the inverse question of finding the best sets of process parameters by minimizing the expected squared deviation between target and actual track geometry. The GPR was trained and validated with a total of 379 cross sections of single tracks and the benefit of the workflow is demonstrated by two exemplary use cases.Item Open Access The high cycle fatigue testing of High‐Performance Concretes using high frequency excitation(2023) Madadi, Hamid; Steeb, HolgerThe effect of fatigue failure in brittle materials like (ultra) High Performance Concrete (UHPC) due to cyclic loading causes unexpected failure that consequently results in heavy costs in marine and civil structures. To characterize the effect of fatigue, cyclic loading tests are performed, and “the number of cycles to failure” are experimentally determined. One problem with these kinds of tests is that such experimental investigations are potentially expensive, i.e., time‐consuming process since the number of loading cycles could be extremely high. Further, within the different damage phases of the cycling tests, one has no access to the small‐scale, i.e., microscopical evolution of (micro‐)cracks. Additionally, a full characterization of the small‐strain stiffness evolution of the material is challenging. The goal of the research investigation is to combine a (large amplitude) High Cycle Fatigue experiment with a (low amplitude) Dynamic Mechanical Analysis (DMA). Using a setup based on the piezoelectric actuator, the (rate‐dependent) mechanical properties of the material in tangential space, and the failure modes of the material will be examined accurately. The excitation frequency is between 0.01 Hz to 1000 Hz which allows for reducing the experimental investigation time to failure. Further, it allows investigating the effect of frequency on the number of cycles to failure. Firstly, experimental results for HPC and berea sandstone samples will be presented. Harmonic experimental data include (direct) strain measurements in axial and circumferential directions as well as forces in axial directions. In addition, the resulting complex Young's modulus and evolving damage‐like “history” of HPC and berea sandstone specimens will be shown.Item Open Access Artificial instabilities of finite elements for nonlinear elasticity : analysis and remedies(2023) Bieber, Simon; Auricchio, Ferdinando; Reali, Alessandro; Bischoff, ManfredWithin the framework of plane strain nonlinear elasticity, we present a discussion on the stability properties of various Enhanced Assumed Strain (EAS) finite element formulations with respect to physical and artificial (hourglassing) instabilities. By means of a linearized buckling analysis we analyze the influence of element formulations on the geometric stiffness and provide new mechanical insights into the hourglassing phenomenon. Based on these findings, a simple strategy to avoid hourglassing for compression problems is proposed. It is based on a modification of the discrete Green-Lagrange strain, simple to implement and generally applicable. The stabilization concept is tested for various popular element formulations (namely EAS elements and the assumed stress element by Pian and Sumihara). A further aspect of the present contribution is a discussion on proper benchmarking of finite elements in the context of hourglassing. We propose a simple bifurcation problem for which analytical solutions are readily available in the literature. It is tailored for an in-depth stability analysis of finite elements and allows a reliable assessment of its stability properties.Item Open Access About the applicability of the theory of porous media for the modelling of non‐isothermal material injection into porous structures(2023) Völter, Jan-Sören L.; Ricken, Tim; Röhrle, OliverIn this contribution we investigate the relevance of the theory of porous media for the non-isothermal modelling of material injection into porous structures. In particular, we provide a model describing the injection of cement during percutaneous vertebroplasty, which is derived by consistently following the theory of porous media. We demonstrate numerically that this model elicits unphysical behaviour under local thermal non-equilibrium conditions. No distinct unphysical behaviour is observed under local thermal equilibrium conditions. We conclude that heuristic modifications of the model equations are necessary and suspect the unphysical behaviour to be caused by contradictory modelling assumptions.Item Open Access Hydraulically induced fracturing in heterogeneous porous media using a TPM‐phase‐field model and geostatistics(2023) Wagner, Arndt; Sonntag, Alixa; Reuschen, Sebastian; Nowak, Wolfgang; Ehlers, WolfgangHydraulically induced fracturing is widely used in practice for several exploitation techniques. The chosen macroscopic model combines a phase‐field approach to fractures with the Theory of Porous Media (TPM) to describe dynamic hydraulic fracturing processes in fully‐saturated porous materials. In this regard, the solid's state of damage shows a diffuse transition zone between the broken and unbroken domain. Rocks or soils in grown nature are generally inhomogeneous with material imperfections on the microscale, such that modelling homogeneous porous material may oversimplify the behaviour of the solid and fluid phases in the fracturing process. Therefore, material imperfections and inhomogeneities in the porous structure are considered through the definition of location‐dependent material parameters. In this contribution, a deterministic approach to account for predefined imperfection areas as well as statistical fields of geomechanical properties is proposed. Representative numerical simulations show the impact of solid skeleton heterogeneities in porous media on the fracturing characteristics, e. g. the crack path.