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In ultra‐high performance concrete (UHPC) embedded micro steel fibres increase the ductility and improve the post cracking load‐bearing behaviour under tensile loading. For an efficent and economical dimensioning of components, especially for fatigue susceptible structures, it is necessary to characterise the crack‐bridging load‐bearing effect of the micro steel fibres and the associated processes...
Concrete exhibits a different deformation behavior in tension and compression when subjected to uniaxial and biaxial loads. It also reveals crack‐opening and crack‐closing effects under cyclic loads. This paper discusses a gradient‐enhanced continuum damage model to investigate the deformation and damage behavior of concrete subjected to cyclic and multiaxial loading conditions. An activating variable...
Wood is an organic porous material of cellulose fibers, which consist of a cell wall and a lumen. In this paper a microstructure‐related model utilizing the polygonal finite element method (PFEM) is presented. The PFEM enables the discrete modeling of the wooden cellular structure under application of shape functions based on mean value coordinates. The numerical integration scheme is based on the...
Reinforced concrete structures are built all over the world. The development of cracks is an unavoidable appearance, based on the interaction of the concrete and the reinforcement. The crack pattern can have an significant influence at the ageing of the structure. The presented modelling concept describes the reinforced concrete on the mesoscale. For the description of the concrete the Discrete Element...
Although isotropic damage models are considered for a first approximation to simulate the deformation behavior of concrete, micro‐cracking of concrete occurring due to the sequential and multi‐directional loads necessitates an anisotropic description of damage for a reliable representation of damage in concrete. The present paper discusses modeling aspects of mechanical degradation behavior of concrete...
The imperfection sensitivity of stiffened cylinders is analysed on the basis of a critical perturbation associated with a minimum of strain energy. To identify worst perturbations including displacements and stresses, the perturbation energy concept is used, which is developed for mixed finite elements. Disadvantages in modelling branched structures due to stress discontinuities are avoided by transferring...
Concrete structures are built extensively all over the world. The prediction of the lifetime of a structure is very important in terms of costs and usability. A numerical modeling concept is presented that can describe concrete on the mesoscale. The focus of the model development is on the coupling of mechanics, heat conduction and chemical reactions. The Discrete Element Method (DEM) is used to describe...
Ultra‐high performance fiber‐reinforced concrete (UHPFRC) is usually applied for thin‐walled and lean constructions because of its excellent mechanical properties. However, these lightweight constructions such as bridge girders, masts, towers, and railway tracks, for example, are susceptible to oscillations due to cyclic loading. A model describing the fatigue behavior of UHPFRC is required. Therefore,...
Ultra‐high performance concrete with a compressive strength of more than 140 N/mm2 reacts very brittle without the addition of fibres. At designing economical and resource‐efficient building components as well as performance‐optimized materials, the supporting effects of the additional microfibres must be considered. Prospectively, cyclic loading and the fatigue behaviour of high performance materials...
The present paper describes a simplified model for isotropic damage developed on continuum damage theory. The model characterizes the distinct behaviour of concrete in tension and compression using a unified equivalent strain, which governs the growth of damage. In reality, concrete exhibits distributed micro‐cracking pattern under multi‐directional loads. Therefore, the model is extended to incorporate...
Es wird ein Berechnungsmodell für 2‐Fluid‐Strömungen mit drehendem Starrkörper vorgestellt, mit dem eine numerische Analyse der Strömungsvorgänge innerhalb von Schaufelwasserrädern möglich ist. Mit dem vorgestellten Berechnungsmodell erfolgt die erstmalige numerische Untersuchung der bei Schaufelwasserrädern auftretenden Strömungsvorgänge. Dabei werden die wesentlichen Punkte im Rahmen der numerischen...
Long‐span bridges may collapse due to the interaction of turbulent wind flow and structural motion. The investigation of the fluid‐structure interaction requires appropriate models for the structure, the wind flow and the coupling between them. Modeling and simulation of the wind flow is still a challenging aspect. The aim of this paper is to show the application of Reynolds Averaged Navier‐Stokes...
An advanced space‐time finite element method is presented to investigate movements of landslides and their interaction with flexible structures. The mechanics of liquefied soil is described by Navier‐Stokes‐equations for visco‐plastic non‐newtonian fluid. Likewise the fluid the kinematics of the structure is described by velocities, taking large rotations into account. This leads to a monolithic fluid‐structure...
An approach to model the deterioration of steel structures is presented by transferring the results of a continuum damage mechanics analysis to an extended beam model which can account for the loss of structural integrity.
Damage starts at the microscopic level by the initiation, growth and coalescence of voids with decreasing material resistance followed by the formation of microcracks at the mesoscale...
Es wird ein Berechnungsmodell vorgestellt mit dem eine numerische Analyse der Überströmung von Verschlussorganen möglich ist. Der Arbeitsschwerpunkt liegt auf der Untersuchung der Stabilität des Lösungsverfahren unter Berücksichtigung der zu wählenden komplexen Randbedingungen sowie der physikalischen und numerischen Parameter. Die Güte der dabei gewonnen Ergebnisse wird mit experimentellen Untersuchungen...
The Discrete Element Method (DEM) is used to model solids under quasi‐static and dynamic loading. In order to model elastic bodies, a microscopic model must be able to represent the macroscopic properties of the material. An energy‐based approach to determine the model parameters is presented for an unit cell assemblage of 13 particles in the hexagonal close packing of spheres. The stored strain energy...
The aim of this study is to investigate elasticity based damage models in which the isotropic damage is driven by different history parameters under uniaxial setting. This leads to a suitable history parameter for the description of material strain‐softening realistically. Existing damage evolution laws from literatures are used to compare the results using strain and energy equivalence principles...
The presented model allows for the description of the most important coupled processes in porous media, whereby focus is laid on concrete structures. It can be employed for a consistent numerical analysis within a monolithic solution algorithm. Mechanical processes are coupled with transport processes, e.g. of energy and humidity, as well as with chemical processes like depassivation due to chloride...
A non‐linear bond model is presented, capturing bond behaviour between concrete and reinforcing ribbed steel bars. An existing model, where coupled thermal‐hygric‐mechanical‐chemical (THMC‐) processes are already modelled for pure concrete, will be extended by the presented bond model. Against this background and due to the resulting requirements the approach of a geometrically consistent consideration...
Die Beweglichkeit von Wasserrinnsalen auf Zylinderoberflächen besitzt beim hydroaeroelastischen Phänomen der Regen‐Wind induzierten Schwingungen, welches bei geneigten Kabeln und Hängern von Schrägkabelbrücken und Bogenbrücken durch gleichzeitiges Auftreten von Regen und Wind entstehen kann, eine elementare Bedeutung für den Erregermechanismus [1]. Bei der Untersuchung des Schwingungsphänomens ist...
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