Doctoral Theses


Andreas Brugger 
Multiphase modelling of strengthening of reinforced concrete structures with concrete overlays
Mehrphasenmodellierung für die Verstärkung von Stahlbetontragwerken mittels Aufbeton
in progress

Mohammad Reza Azadi Kakavand
Performance of damage-plastic models for concrete failure under cyclic loadings
in progress

Magdalena Schreter
Impact of different rock models on the predicted response of the rock-support system of deep tunnels
in progress

Martin Drexel
Untersuchung des Druck- und Zugkriechens von Beton unter Berücksichtigung des Feuchtegehalts
in progress

Matthias Neuner 2018
Numerical and Experimental Modeling of Shotcrete and Application to Finite Element Analyses of Deep Tunnel Advance

The present thesis deals with the description of the material behavior of shotcrete, with special focus on applications in numerical simulations of deep tunnel advance. To this end, a new material model for shotcrete is proposed, which is based on three continuum models for concrete. They comprise the damage plasticity model for concrete by Grassl and Jirásek, the solidification theory for concrete creep by Bažant and Prasannan, and the semi-empirical model by Bažant and Panula for describing shrinkage.

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Matthias Aschaber 2017
Development and Application of a three-phase-model for concrete

This thesis deals with the development and application of a three-phase-model for concrete on the basis of the theory of porous materials. Starting from the microscopic balance equations the macroscopic balance equations of a multi-phase-system are derived. Due to the existing pore structure, caused by hydration, concrete is a porous material and moisture within the pores can be transported and stored.

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Benjamin Fuchs 2016
A three-dimensional constitutive model for anisotropic rockmass and its numerical implementation within the framework of the FEM

This work deals with the presentation of a constitutive model for isotropic rock and its extension to anisotropic material behaviour. Beside the model definition, the focus is put on the stress update procedures, the identification strategies for the model parameters and the validation of the model by laboratory results.

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David Unteregger 2015
Advanced constitutive modeling of intact rock and rock mass

The mechanical behavior of intact rock and rock mass is of great interest for various kinds of underground excavations, e.g. for deep tunnel advance and construction of underground caverns. The finite element method and other numerical methods are powerful tools for analyzing such complex three-dimensional rock mechanical problems. However, obtaining reliable results from such simulations is a demanding task. A key aspect is modeling the complex, non-linear constitutive behavior of intact rock and rock mass involved.

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Xin Ma 2015
Large-scale 3D numerical simulations of geotechnical problems involving multi-phase soil models

In the present work, a multi-phase model for partially saturated soils is implemented into the open-source FE-program OpenSees [76]. The code is employed on a high performance cluster system, the efficiency of the program is optimized and tested by a numerical study focussing on numerical simulations of geotechnical problems.

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Tobias Cordes 2013
Mechanische Eigenschaften von Grenzschichten zwischen zementgebundenen Materialien

This thesis is concerned with the development of a constitutive model for cementitious bimaterial interfaces and investigations for the quantification of their fracture properties. To this end, the constitutive model is implemented into a finite element analysis program system and validated by numerical simulations of small scale tests.

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Bernhard Valentini 2011
A three-dimensional constitutive model for concrete and its application to large scale finite element analyses

This thesis deals with the critical evaluation, comparison and further development of three-dimensional constitutive models for concrete, the implementation of an enhanced constitutive model for concrete into a finite element analysis program system, the validation of the concrete model and its application to three-dimensional large scale finite element analyses. To this end, the solution procedure of the stress update at the integration point level has to be robust, accurate and efficient. Hence, different solution procedures for the stress update, based on an implicit integration algorithm, are compared and verified with respect to their robustness, accuracy and efficiency at the integration point level and the structural level, respectively.

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Michael Pertl 2010
Grundlagen, Implementierung und Anwendung eines Drei-Phasen Modells für Böden

In the present work a multi-phase model for partially saturated soils is developed. The theoretical basis of the model is described and the governing equations for a finite element formulation are derived and implemented in a finite element program. The numerical model is verified by a numerical study and applied to the numerical simulation of geotechnical problems.

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Matthias Hofmann 2010
Integrationsalgorithmen und Parameteridentifikation elasto-plastischer Stoffgesetze für teilgesättigte Materialien

The integration of elasto-plastic constitutive models for determining the stresses is an important part of nonlinear finite element analyses. This thesis deals with the stress update of elasto-plastic material models for partially saturated materials.

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Yvonne Theiner 2007
Ein Beitrag zur Modellierung der Rissbildung in Beton

In the present thesis a numerical model for the simulation of crack formation in concrete structures is introduced. It concerns the further development of a crack model formulated within the framework of the strong discontinuity approach (SDA) employing the concept of elements with embedded discontinuities. This crack model is characterized by considering jumps in the displacement field due to crack formation, which may cross a chosen discretization in arbitrary ways.

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Roman Kohler 2006
Numerical Modelling of Partially Saturated Soils in the Context of a Three Phase FE Formulation

The present thesis deals with the development and validation of a constitutive model for the mechanical behavior of partially saturated soils and its implementation into a three-phase FE-formulation. Such numerical models can be applied to the simulation of a broad range of geotechnical problems covering consolidation, drying and wetting of soils under atmospheric conditions as for instance after the impoundment of an earth dam as well as dewatering by means of compressed air e.g. in the context of tunneling below the groundwater table.

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Christian Feist 2004
A numerical model for cracking of plain concrete based on the strong discontinuity approach

The present thesis is devoted to the development of a family of finite elements which are capable to resolve fracture processes in plain concrete structures. From the mathematical point of view the formation of discrete cracks can be considered as the development of discontinuity surfaces exhibiting displacement jumps. The strong discontinuity kinematics offer an appropriate description of the kinematics of solids crossed by such discontinuity surfaces.

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Robert Stelzer 2003
Adaptive Finite Element Analysis of Multi-Phase Problems

In the present thesis adaptive finite element procedures for multi-phase problems are developed and investigated. The considered multi-phase problems refer to porous soils, consisting of a soil skeleton and one or two fluid phases, in particular water and (compressed) air. Coupled formulations for soils can be applied to a broad range of geotechnical problems, covering consolidation, dewatering of soils under atmospheric conditions, as well as by means of compressed air and tunneling below the groundwater table.

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Gerhard Öttl 2003
A Three-Phase FE-Model for dewatering of soils by means of compressed air

Das Ziel der Arbeit besteht in der Entwicklung eines numerischen Modells zur Simulation des Tunnelvortriebes unter Grundwasser mit Berücksichtigung der Grundwasserverdrängung im Bereich der Ortsbrust durch Druckluft. Die Verformungen im Boden werden bei einem derartigen Problem sowohl durch die Entwässerung des Bodens als auch durch den Tunnelvortrieb verursacht.

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Bernhard Josef Winkler 2001
Traglastuntersuchungen von unbewehrten und bewehrten Betonstrukturen auf der Grundlage eines objektiven Werkstoffgesetzes für Beton

Traglastuntersuchungen von Betonstrukturen mit Hilfe der Methode der finiten Elemente ermöglichen die numerische Simulation des nichtlinearen Tragverhaltens bis zum Eintritt des Versagens. Hierbei spielt die mathematische Formulierung des Zug- und Druckversagens eine entscheidende Rolle. Ziel dieser Arbeit ist die Entwicklung eines elasto-plastischen Werkstoffmodells für unbewehrten und bewehrten Beton, die experimentelle Verifizierung und die numerische Simulation des Tragverhaltens mit Hilfe der Methode der finiten Elemente.

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Roland Hinterhölzl 2000
Modeling the time dependent behavior of fiber reinforced plastics and particulate composites by the theory of viscoelasticity and damage mechanics

Reinforced plastics show a strong time dependent behavior that is introduced by the time dependent behavior of the matrix whereas the reinforcing fibers or particles are usually time independent, see fig. 1. The aim is to model this behavior by the theory of viscoelasticity and non-linear effects within the theory of continuum damage mechanics.

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Günther Schullerer 2000
A numerical investigation for the analysis of fiber reinforced composites with respect to macromechanical and micromechanical modeling

Ziel dieser Arbeit ist die Entwicklung eines Verbundmodells, welches als User - Element in das FE - Programmsystem ABAQUS eingebunden wird. Als Freiheitsgrade eines repräsentativen Volumenelementes (RVE) werden Matrixverschiebungen und Faser Relativverschiebungen in Faserlängsrichtung definiert, welche über das Interface - Stoffverhalten miteinander verknüpft sind. Damit ist es möglich, die Beanspruchung in den Einzelkomponenten eines ebenen FKV zu errechnen.

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Johannes Jäger 1996
Numerische Behandlung anisotrop plastischer Stoffgleichungen für Böden

Siegfried Ebenbichler 1996
Ebene Berechnung des Stranggießprozesses in gemischt Euler-Lagrangeschen Koordinaten

Herbert Haller 1995
Modell für elasto-plastische Schädigung