Teaching

Teaching activities comprise lectures on strength of materials including continuum mechanics, structural analysis (beams, slabs and shells) and finite element methods for students in Civil and Environmental Engineering at the Bachelor, Master and Ph.D. level. In addition, lectures are given to students in Mechatronics. Additional lectures on specialized topics have been prepared for the doctorate programme “Computational Interdisciplinary Modelling”.

 

Masters Theses

Lisa Molling 2018
Modeling of Soil-Water Characteristic Curves with Hysteresis

Stefan Smaniotto 2018
Untersuchung des Schwindverhaltens von Normalbeton unter Berücksichtigung des Feuchtegehalts

Andreas Brugger 2017
Finite-Elemente-Modellierung von Bewehrung: Grundlagen, Implementierung und Simulation

Matthias Neuner 2014
Entwicklung und Dokumentation eines Kriechprüfstands

Christian Huber 2013
Numerische Simulationen mit einem Mehr-Phasenmodell für Beton

Martin Drexel 2013
Dokumentation der Sanierung einer Brücke

Stephan Aberer 2012
Experimentelle und numerische Studien zum zeitabhängigen Tragverhalten von Verbundankern

 

Lisa MOLLING 2018
Modeling of Soil-Water Characteristic Curves with Hysteresis

The present thesis deals with the modelling of hysteresis in the soil-water characteristic curve, a phenomenon which is observed for processes involving drying and wetting of porous materials like soils and concrete. The soil-water characteristic curve describes the relation between capillary pressure and saturation. Its shape depends on the shapes of the pores as well as on the pore size distribution and is therefore different for different materials.

Three different models are used in order to describe the soil-water characteristic curve. The first one is the equation of van Genuchten. This widely-used model includes no hysteresis, i.e. the same behaviour is assumed for drying and wetting. This model is contrasted with two hysteretic models. The Nuth model uses the formulation of an elasto-plastic constitutive law. The hysteretic effect originates from kinematic hardening, i.e. from a shifting of the elastic range triggered by plastic wetting or drying. The Pedroso model is based on reference curves. Different curves are implemented to represent the drying and wetting path. Their shape is determined by adaption to experimental data. Both hysteretic models are formulated incrementally. The Nuth model exhibits kinks on the drying and wetting path. For the Pedroso model drying as well as wetting paths are smooth.

The implementation of the mathematical models is described. The calibration is carried out on the basis of data for two materials, Del Monte Sand and ordinary concrete. The data for the calibration of the sand is taken from the literature. The measured data used for the calibration of the models for concrete is taken from an experiment to determine the sorption isotherm of ordinary concrete which was conducted at the Unit of Strength of Materials and Structural Analysis. The calibration is more difficult for the more complex models. Nevertheless, a good adaption to the given set of data points is achieved for all models.

All three models are implemented into a multi-phase finite element software. The thesis reviews the basic assumptions and equations for the multi-phase formulation. Results for the desiccation and subsequent watering of a sand column are shown. For this simulation, the parameters obtained from the calibration for the Del Monte Sand are used as input. The hysteretic effect manifests itself in a delay in the watering process. The results are consistent with values from the literature. The comparison of the investigated hysteretic models shows that the Pedroso model is numerically more stable. This behaviour is attributed to the smooth behaviour inherent to its formulation.

 

 

Stefan SMANIOTTO 2018
Untersuchung des Schwindverhaltens von Normalbeton unter Berücksichtigung des Feuchtegehalts

As a consequence of the increasing traffic load as well as of the progression of the mean age of bridges, measures of rehabilitation become more and more important. One such measure could be adding a concrete overlay. Therefore, the aim of this master thesis is to provide a better understanding of the material parameters related to shrinkage and parameters for multiphase modeling.

First, a brief introduction to the subject is given. Subsequently, the theoretical foundation is discussed and the concepts of porosity, moisture storage and moisture transport are introduced. Furthermore, the sorption isotherms are defined and the different shrinkage processes are briefly explained.

The composition of the concrete mixture with (compressive) strength class C30/37 is specified as well as the fresh concrete parameters, which are measured during the concreting. In addition to that, the parameters of the hardened concrete, such as Young’s modulus and the compressive strength, are provided for different concrete ages. Additionally the determination of the hygric parameters is presented, with the desorption isotherms as well as the adsorption isotherms being determined on thin concrete slices.

Furthermore, the laboratory tests and the results of the shrinkage tests on thin specimens are described. In the test program the autogenous shrinkage, the pure drying shrinkage and the combined autogenous and drying shrinkage are investigated. The autogenous shrinkage was determined on sealed specimens from the age of one day, whereas the drying shrinkage is measured on two years old specimens, which were therefore completely hydrated. Likewise, the combined autogenous shrinkage and drying shrinkage are determined using specimens from the age of one day, which were simultaneously drying and hydrating. Moreover, the influence of the concrete age on the combined autogenous and drying shrinkage is analysed. Next, the obtained results of the tests are compared to different codes as well as to results of other authors.

In addition, the deformation of young concrete, starting at the age of 5 hours, is observed on prismatic specimens. Simultaneously, the temperature development is measured in the above-mentioned prismatic sample bodies, as well as in a semi-adiabatic experiment using a cubic specimen. All specimens were stored in a climatic chamber at a temperature of (20 ± 1) °C.

Finally, a summary of all the obtained results is provided and a brief outlook is given.

 

 

Andreas BRUGGER 2017
Finite-Elemente-Modellierung von Bewehrung: Grundlagen, Implementierung und Simulation

The structural analysis of reinforced concrete parts using the finite element method does not only require an appropriate modelling of the material behaviour of concrete, but also an adequate consideration of the reinforcing steel. In this thesis the modelling of the latter component as embedded reinforcement is examined. This concept is characterised by the superposition of those finite elements that represent concrete and reinforcement. This approach offers a realistic reproduction of the load bearing behaviour and is suited for system level Analysis.

There are different methods of applying the concept of embedded reinforcement. According to comprehensive preliminary investigations that have been carried out within the present thesis, the element-based embedding proves to be advantageous. The distinguishing feature of this method is the partitioning of the reinforcing bars along the boundaries of the elements representing the concrete. The obtained segments are clearly assigned to the concrete elements. This approach requires the calculation of intersection points. This procedure as well as the actual embedding on the level of the element stiffness matrix are explained in the present Thesis.

In order to allow meaningful calculations the concept of embedded reinforcement for two-dimensional problems has been implemented into a capable finite element routine. This software package as well as the material model which was applied to describe the concrete have been continually developed at the Unit of Strength of Materials and Structural Analysis at the University of Innsbruck. By recalculating the tensile tests of reinforced concrete specimens it was possible to examine the consideration of tension stiffening. The calculations show an inaccurate load bearing behaviour if tension stiffening is neglected, whereas a modification of the material model for concrete leads to appropriate results. Furthermore, system level analyses of L-shaped concrete panels under bending were carried out in order to investigate the performance of the concept of embedded reinforcement. Although linear elastic behaviour has been assumed for the reinforcing steel, promising results could be obtained. In addition to a good depiction of the crack formation in the form of concentrated damage zones, the concept of embedded reinforcement allows a detailed examination of the load bearing behaviour of the individual reinforcing bars. The consideration of nonlinear behaviour for the reinforcing steel and the associated reduction of tension stiffening are expected to allow accurate ultimate load calculations.

 

 

Matthias NEUNER 2014
Entwicklung und Dokumentation eines Kriechprüfstands

The subject of this master thesis is the documentation and development of a creep-test bench, which was developed in the years 2013 and 2014 at the Unit for Strength of Materials and Structural Analysis. During this development, three identical test benches have been built up and are currently used in experiments which started in September 2014. The aim of these creep-test benches is to gain measurement data on the creep of concrete over a long time period. For this purpose, a constant stress is applied on two specimens in the test bench. While keeping up this stress, the strain, which is increasing due to creep, is measured regularly. The objectives of this thesis were to specify the requirements, the assembly and documentation of a repeatable adjustment of the test bench. Further on, a sensory system to record all important measurement data has been composed and an application for reading the data has been developed.

Finally, the complete process to prepare, start and monitor an experiment at the test bench has been documented, to give accurate instructions for future test series.

 

 

Christian HUBER 2013
Numerische Simulationen mit einem Mehr-Phasenmodell für Beton

This master thesis deals with the creep and shrinkage behavior of concrete. Results from different experiments will be compared to the results of numerical simulations based on a multi-phase model of concrete.

The basic principles of the multi-phase model will be discussed. This contains descriptions of the theory of porous media, the hygric behaviour of concrete, the hydration process of concrete and the mathematical formulation of concrete creep and shrinkage behaviour. Furthermore, the basic principles of the implementation of a multi-phase model of concrete by means of the FEM is shown.

The larger part of this thesis deals with the comparison of the computed and in different experiments measured strains and relative mass water contents and their interpretation. For the comparison of drying shrinkage strains, results from experiments conducted at the University of Innsbruck, Unit for Strength of Materials and Structural Analysis, were used. Experiments of Bryant and Vadhanavikkit were used for the comparison of creep strains. For all numerical simulations, a good agreement with the experimental results was achieved.

 

 

Martin DREXEL 2013
Dokumentation der Sanierung einer Brücke

Due to increasing traffic loads and a relatively high mean age of existing concrete bridges, strengthening measures like adding a concrete overlay are becoming more important. The present work deals with monitoring of an existing bridge strengthened by adding a concrete overlay in order to improve the load bearing capacity. Comparison of in-situ-measurements with results of an accompanying lab test shows the effect of environmental influences on determined measurements.

After a short introduction to the current topic in the first chapter as well as a short introduction of the existing concrete bridge in the second chapter, the third chapter introduces the theoretical basics of porosity, moisture storage, moisture transport as well as different types of shrinkage.

At the beginning of the fourth chapter the comprehensive lab test is described and the results are presented. Furthermore, special measuring instruments used on the in-situ-test are explained and the determined in-situ-measurements are described. Afterwards, lab test results are compared with in-situ-measurements as well as with the results calculated according to Euro-code 2 (EN 1992-1-1 [1]).

The fifth chapter gives an outlook on future work. The sixth and last chapter contains a summary of the major findings of the present work.

 

 

Stephan ABERER 2012
Experimentelle und numerische Studien zum zeitabhängigen Tragverhalten von Verbundankern

There are two different kinds of fastening processes; cast-in-place installations and post-installed installations. The latter has a significantly lower planning effort. Furthermore, one must differentiate between mechanical and chemical systems. While mechanical anchors transfer the applied force into the base material at one point, chemical anchors do this always over the drilling hole's entire area. In the following thesis, the Finite Element Method is used to numerically analyze the time-dependent behaviour of chemical anchors. While the latter is well known for concrete and steel, it still needs to be investigated for chemical mortar systems. The time dependent deformations caused by a constant load, the so-called creep deformations, are defined by compliance functions, where different kinds of formulations are available. For this purpose three different mortar systems are investigated experimentally.

 Furthermore, results of long-term experiments for different mortar systems are compared with simulation results. The correspondence between simulation and experiment is good. This means, that the experimentally determined compliance function can be validated. Parameter studies show the significance of several influencing factors, for example, the scatter of experimental data or the interpolation error in the course of determining the compliance function.