Josef Eberhardsteiner

Vienna University of Technology, Wien, Vienna, Austria

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Publications (118)100.45 Total impact

  • L. Wagner, T.K. Bader, J. Eberhardsteiner, K. de Borst
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    ABSTRACT: Fungal degradation is among the greatest hazards for standing trees as well as timber constructions. Herein we aim at gaining more detailed insight into the degradation strategies of wood destroying fungi and the consequences on the mechanical performance of wood. At the macroscale, the occurring losses of mass and of mass density mask effects of altered chemical composition and microstructure. Thus, it is necessary to step down the hierarchical organization of wood to the cell wall scale in order to resolve these changes and their mechanical impact. We present a multiscale micromechanical model which is used to estimate the stiffnesses of the S2 cell wall layer and the compound middle lamella of fungal degraded wood. Data from a detailed chemical, microstructural and micromechanical characterization of white rot and brown rot degraded Scots pine sapwood is analyzed. Comparing predicted cell wall stiffnesses with measured ones confirms the suitability of the approach. The model enables to establish structure–stiffness relationships for fungal degraded wood cell walls and to test hypotheses on yet unknown effects of fungal decay. The latter include the evolution of porosity, modifications of the cell wall polymers resulting in changes of their stiffnesses, as well as increasing cell wall crystallinity. The model predictions in general showed good agreement with the predictions not considering pores in the cell wall. However, this finding does not rule out the formation of porosity. Other degradation related effects like modifications of the cell wall polymers as well as increased crystallinity have the potential to account for stiffness decreases upon the formation of pores.
    International Biodeterioration & Biodegradation 09/2014; 93:223–234. · 2.24 Impact Factor
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    M. Lukacevic, J. Füssl, M. Griessner, J. Eberhardsteiner
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    ABSTRACT: In wooden boards, knots and the resulting fibre deviations in their vicinities are mainly responsible for qualitative downgrading of timber elements. Thus, the development of reliable numerical simulation tools for the determination of effective strength and stiffness properties of timber elements and, in a next step, for the development and evaluation of grading criteria is highly desirable. Due to the complexity of such tools, a comprehensive validation is required. Within this work, the suitability of full-field deformation measurements for four-point bending tests on wooden boards with knots is evaluated first. Next, the test series is used to validate a previously developed three-dimensional numerical simulation tool, which combines a geometrical model for the grain course and a micromechanical model for a density and moisture dependent characterisation of the clear-wood material. The digital image correlation technique proved to be capable to reproduce the strain fields in the vicinity of knots under bending load. Moreover, a very good correlation between numerical and experimental results was obtained.
    Strain 05/2014; · 0.92 Impact Factor
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    Thomas K. Bader, Karin de Borst, Josef Eberhardsteiner
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    ABSTRACT: In this contribution, a micromechanical modeling approach in the framework of poromechanics is adopted to study structure-stiffness relations of two quite different species, namely spruce and yew, in detail. In particular, microstructural specialties of yew and spruce are assessed. A dominant influence of the cellulose content and its orientation on the stiffness of the cell wall is revealed, while on the macroscopic scale, density is found to be the governing microstructural characteristic for elastic properties. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)
    PAMM 12/2013; 13(1).
  • G. Hochreiner, J. Füssl, E. Serrano, J. Eberhardsteiner
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    ABSTRACT: Although cross-laminated timber (CLT) plates are increasingly used in high-performance building structures, a tailored composition of them or, at least, a performance-based classification scheme is not available. Especially, the influence of the quality of the ‘raw’ material (wooden boards) on the load carrying capacity of CLT elements is hardly investigated yet. For this reason, within this work, bending tests on 24 CLT plates consisting of wooden boards from three different strength classes have been carried out. The global mechanical response as well as the formation of failure mechanisms were investigated, including a full-field deformation measurement system, which allowed for a qualitatively as well as quantitatively identification of board failure modes. Interestingly, no influence of the board strength class on the elastic limit load of the CLT plates was observed, but the situation was different for the load displacement history beyond the elastic regime, where basically, two different global failure mechanisms could be distinguished. The obtained knowledge about the ‘post-elastic’ behaviour of CLT plates may serve as a basis for the optimisation of CLT products and the development or improvement of design concepts, respectively. Moreover, the obtained large ‘post-elastic’ capacity reserve of CLT consisting of high quality boards could lead to a better utilisation of the raw material.
    Strain 12/2013; · 0.92 Impact Factor
  • J. Füssl, R. Lackner, J. Eberhardsteiner
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    ABSTRACT: The main failure mechanisms of flexible pavements, such as low-temperature cracking, fatigue failure, and rutting are strongly influenced by the viscoelastic properties of asphalt. These viscoelastic properties originate from the thermorheological behavior of bitumen, the binder material of asphalt. In this paper, the bitumen behavior is studied by means of a comprehensive experimental program, allowing the identification of viscoelastic parameters of a power-law type creep model, indicating two time scales (short-term and long-term) within the creep deformation history of bitumen. Moreover, these characteristics of the creep deformation transfer towards bitumen-inclusion mixtures, as illustrated for mastic, consisting of bitumen and filler. For this purpose, the aforementioned power-law creep model is implemented into a micromechanical framework. Finally, the activation of the different creep mechanisms as a function of the loading rate is discussed, using viscoelastic properties obtained from both static and cyclic creep tests.
    Meccanica 11/2013; · 1.82 Impact Factor
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    ABSTRACT: Wood is enjoying increasing popularity in the building sector. In order to fully exploit the potential of this material, particularly in two and three-dimensional structures, improved knowledge of the mechanical behavior of the material and more complex constitutive models are required. We herein present a holistic approach to mechanical material modeling of wood, including a multitude of length scales as well as computational and experimental efforts. This allows to resolve the microstructural origin of the macroscopic material behavior and to finally apply the gained knowledge to structural applications in a timber engineering framework. Focusing on elastoplasticity and viscoelasticity, exemplary results of the performed investigations are presented and their interrelations discussed. Regarding computational approaches, presented developments include multiscale models for prediction of elastic limit states and creep compliances of wood, macroscopic phenomenological models for wood plasticity and the time and moisture-dependent behavior, and their applications to investigations of dowel-joints and glued-laminated timber beams. Accompanying experiments provided additional input data for the computational analyses, therewith completing the set of material properties predicted by the multiscale models. Moreover, they served as the reference basis for model validation at both the material and the structural scale.
    Computers & Structures 10/2013; 127:53-67. · 2.18 Impact Factor
  • G. Hochreiner, J. Füssl, J. Eberhardsteiner
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    ABSTRACT: Since wood products for structural elements, especially cross-laminated timber (CLT), have gained importance in the building sector, the need for appropriate and reliable design codes for such wood products has become essential. For the improvement and development of design concepts, a profound knowledge about the mechanical behaviour of these products is necessary. For this reason, this work focuses on global failure mechanisms and the corresponding evolution of different crack modes in CLT plates, depending on geometric and/or material related properties. Therefore, plate-bending experiments on three- and five-layered CLT plates were carried out. In addition to standard evaluation methods, each specimen was cut into small cubes to identify the failure modes inside the plates. Regions with dominant shear failure, tensile failure, delamination and mixed failure modes could be captured and connected to geometry and loading situation. Based on this evaluation, well-known but not yet in detail described effects, such as the ductile structural behaviour of CLT plates, can be explained. Moreover, the evolution of rolling shear failure modes as well as from which point the progressive failure highly affects the plate stiffness is investigated and analysed in detail.
    Strain 10/2013; · 0.92 Impact Factor
  • Ninth International Conference on Creep, Shrinkage, and Durability Mechanics (CONCREEP-9); 09/2013
  • Fifth Biot Conference on Poromechanics; 06/2013
  • T. Ring, M. Zeiml, R. Lackner, J. Eberhardsteiner
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    ABSTRACT: The material degradation of concrete subjected to fire events has a severe influence on the load-carrying capacity of support structures. Spalling of concrete layers, exposing the reinforcement bars and degradation of the material properties (Young's modulus, compressive strength) may lead to significant damage of the reduced cross-section and, therefore, cause failure of the structure. In order to understand the stress build-up at the heated surface caused by thermal expansion due to fire loading, finally leading to damage and spalling of concrete, the strain behaviour of cement paste and concrete exposed to combined thermo-mechanical loading is the focus of this work. Hereby, the evolution of thermal strains, Young's modulus and Poisson's ratio with increasing temperature are investigated experimentally. For this purpose, the specimens are loaded uniaxially while the temperature is increased up to 800 °C. The obtained results provide the proper basis for the development of realistic material models, allowing more sophisticated simulations of structures exposed to fire.
    Strain 06/2013; 49(3). · 0.92 Impact Factor
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    ABSTRACT: Strengths of cement pastes with different mixture properties and maturities depend in a very similar overlinear fashion on the gel–space ratio, which is the ratio of the volume of hydration products over the volume of both hydration products and capillary pores. We here investigate the underlying microstructural effects by the experimentally validated micromechanics model of Pichler and Hellmich [CemConRes 41(5), 2011]. This model shows that the macrostrength of cement pastes are not only triggered by the capillary porosity, but also by a strengthening effect of unhydrated clinker “reinforcements” which are embedded as inclusions in the hydrate foam. The analysis is continued with quantifying the strength of the hydrates, in terms of an extended model validation activity. Satisfactory model performance is the motivation to present model predictions for the biaxial compressive failure envelopes of cement pastes, again as a function of gel–space ratio.
    Cement and Concrete Research 03/2013; 45:55–68. · 3.85 Impact Factor
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    ABSTRACT: Many problems in engineering sciences can be described by linear, inhomogeneous, m-th order ordinary differential equations (ODEs) with variable coefficients. For this wide class of problems, we here present a new, simple, flexible, and robust solution method, based on piecewise exact integration of local approximation polynomials as well as on averaging local integrals. The method is designed for modern mathematical software providing efficient environments for numerical matrix-vector operation-based calculus. Based on cubic approximation polynomials, the presented method can be expected to perform (i) similar to the Runge-Kutta method, when applied to stiff initial value problems, and (ii) significantly better than the finite difference method, when applied to boundary value problems. Therefore, we use the presented method for the analysis of engineering problems including the oscillation of a modulated torsional spring pendulum, steady-state heat transfer through a cooling web, and the structural analysis of a slender tower based on second-order beam theory. Related convergence studies provide insight into the satisfying characteristics of the proposed solution scheme.
    Advances in AppliedMathematics and Mechanics. 01/2013; 5(3):269-308.
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    Michael Dorn, Karin De Borst, Josef Eberhardsteiner
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    ABSTRACT: Keywords: Dowel-type timber connections Johansen theory Uniaxial tension tests on connections Ductile and brittle failure modes Influence of density Connection design and dowel roughness Comparison with design rules in Eurocode 5 a b s t r a c t Dowel-type connections are commonly used in timber engineering for a large range of structural appli-cations. The current generation of design rules is largely based on empiricism and testing and lacks in many parts a stringent mechanical foundation. This often blocks an optimized use of the connections, which is essential for the design of economically efficient structures. Moreover, it severely limits the applicability of the design rule, such as restrictions regarding splitting behavior or maximum ductility (e.g. maximum allowable deformations) are missing. Therefore, the demands due to a large and quickly evolving variety of structural designs in timber engineering are not reflected. The aim of this work is to study the load-carrying behavior of the connection in detail, including all loading stages, from the initial contact between dowel and wood up to the ultimate load and failure. Dis-tinct features during first loading as well as during unloading and reloading cycles are identified and dis-cussed. The knowledge of the detailed load-carrying behavior is essential to understanding the effects of individual parameters varied in relation to the material and the connections design. The suitability of the current design rules laid down in Eurocode 5 (EC5) is assessed and deficiencies revealed. Tests on 64 steel-to-timber dowel-type connections loaded parallel to the fiber direction were per-formed. The connections were single-dowel connections with dowels of twelve millimeter diameter. The test specimens varied in wood density and geometric properties. Additionally, the effects of dowel roughness and lateral reinforcement were assessed. The experiments confirmed that connections of higher density show significantly higher ultimate loads and clearly evidenced that they are more prone to brittle failure than connections using light wood. The latter usually exhibit a ductile behavior with an extensive yield plateau until final failure occurs. With increased dowel roughness, both, ultimate load and ductility are increased. The test results are compared with corresponding design values given by EC5 for the strength and the stiffness of the respective single-dowel connections. For connections of intermediate slenderness, EC5 provided conservative design values for strength. Nevertheless, in some of the experiments the design values overestimated the actual strengths considerably in connections of low as well as high slenderness. As for the stiffness, a differentiation according to the connection width is missing, which gives useful results only for intermediate widths. Furthermore, the test results constitute valuable reference data for validating numerical simulation tools, which are currently a broad field of intensive interest.
    Engineering Structures 01/2013; 47:67-80. · 1.77 Impact Factor
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    ABSTRACT: Hygroexpansion of wood is a known and undesired characteristic in civil engineering. When wood is exposed to changing environmental humidity, it adsorbs or desorbs moisture and warps. The resulting distortions or - at restrained conditions - cracks are a major concern in timber engineering. We herein present a multiscale model for prediction of the macroscopic hygroexpansion behavior of individual pieces of softwood from their microstructure, demonstrated for spruce. By applying poromicromechanics, we establish a link between the swelling pressure, driving the hygroexpansion of wood at the nanoscale, and the resulting macroscopic dimensional changes. The model comprises six homogenization steps, which are performed by means of continuum micromechanics, the unit cell method and laminate theory, all formulated in a poromechanical framework. Model predictions for elastic properties of wood as functions of the moisture content closely approach corresponding experimental data. As for the hygroexpansion behavior, the swelling pressure has to be back-calculated from macroscopic hygroexpansion data. The good reproduction of the anisotropy of wood hygroexpansion, based on only a single scalar calibration parameter, underlines the suitability of the model. The multiscale model constitutes a valuable tool for studying the effect of microstructural features on the macroscopic behavior and for assessing the hygroexpansion behavior at smaller length scales, which are inaccessible to experiments. The model predictions deliver input parameters for the analysis of timber at the structural scale, therewith enabling to optimize the use of timber and to prevent moisture-induced damage or failure.
    Interaction and multiscale mechanics. 09/2012; 5(3).
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    ABSTRACT: Structures may fail due to a myriad of different causes. Often, distinction is made between structural and material failure, that means a structure can fail, while the material is still intact (this is the case in so-called stability loss), or the material fails, which, as consequence, may lead to structural failure. The material behavior may turn out difficult to be mathematically guessed at the macro-level. On the other hand, a lot may be known about the chemistry or the microstructure of the material of interest. Herein, we aim at categorizing different scenarios which in the end provoke structural failure, discussing various cases investigated during the last five years, at the Institute for Mechanics of Materials and Structures of Vienna University of Technology: A well-chosen eigenvalue problem shows considerable potential for categorizing stability loss. We then turn to complex composite materials with a hierarchical organization, where a single constituent dominates the overall quasi-brittle failure of the material, such as lignin in wood and wood products, or the cement–water reaction products (shortly called hydrates) in cement-based materials. The picture changes if the first inelastically behaving constituent is related to ductile load carrying, then the loads within the microstructure are re-distributed before the overall material fails: this turns out to be the case in bone. Finally, due to highly confined multiaxial stress states, the elastic portion of the overall energy invested into the material may become negligible—and then yield design analysis employed on material volumes gives an idea of the highly ductile behavior of complex confined materials, such as asphalt. What integrates all the reported cases is the high capacity of mature mathematical and mechanical formulations to reveal the intricate, yet decipherable nature of the (continuum) mechanics of materials and structures.
    Acta Mechanica 09/2012; 223(9). · 1.27 Impact Factor
  • T.K. Bader, K. Hofstetter, J. Eberhardsteiner, D. Keunecke
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    ABSTRACT: Yew (Taxus baccata L.) exhibits among conifers a unique macroscopic elastic behaviour. For example, it shows a comparatively low longitudinal elastic modulus related to its comparatively high density. We herein explore the microstructural origin of these peculiarities, aiming at the derivation of microstructure–stiffness relationships. We measure stiffness properties of yew at different hierarchical levels and compare them to corresponding stiffnesses of Norway spruce (Picea abies [L.] Karsten). Cell wall stiffness is investigated experimentally by means of nanoindentation in combination with microscopy and thermogravimetric analysis. On the macroscopic level, we perform uniaxial tension and ultrasonic tests. Having at hand, together with previously reported stiffnesses, a consistent data set of mechanical, chemical and physical properties across hierarchical levels of wood, we discuss influences of microstructural characteristics at different scales of observation. Moreover, a micromechanical model is applied to predict trends of effects of the microstructure on the investigated stiffness properties. On the cell wall level, particularly, the amount of cellulose and its orientation – which was earlier reported to be distinctly different for yew and spruce – result in differences between the two considered species. On the macroscopic scale, model predicted effects of the annual ring structure on transverse stiffness and shear stiffness are found to be smaller than effects of the microfibril angle and mass density.
    Strain 08/2012; 48(4):306-316. · 0.92 Impact Factor
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    ABSTRACT: PURPOSE: The purpose of our study was to evaluate the initial fixation strength of bridging techniques compared to other suture techniques for rotator cuff repair using a biomechanical animal model, which incorporated pretesting of intact tendons. METHODS: Seventy-six fresh bovine shoulders were used for testing seven suture configurations including simple suture (SS), mattress suture (MS), Mason-Allen (MA), modified double row (mDR), SpeedBridge (SpB), SpeedBridge with medial fixation (mSpB), and double-mattress SutureBridge (dmSuB) techniques. Cyclic loading was performed with all intact bone-tendon complex before (pretest) and after repair of the tendon (main test) at the level of 10 and 180 N at 100 Hz with displacement-controlled ramps of ±33 mm/s. The pretest was stopped after 200 cycles. For the main test, the loading scheme was continued for a maximum of 500 cycles or until failure. RESULTS: The mean elongation of all 76 intact tendons measured at the pretest was 3.8 ± 0.6 mm (2.4-5.4 mm). No differences of gap formations at the 1st cycle were detected between SS, MS, MA, and mDR. SpB showed significant higher gap formations compared to all other suture techniques (p = 0.001). No significant differences were detected between mSpB and dmSuB, whereas both techniques were significant different when compared to the other groups (p < 0.05). CONCLUSIONS: In this study, results showed that bridging techniques with medial fixations have superior initial repair strength compared to other suture techniques. Knowledge of initial fixation strength of rotator cuff repair techniques may be of informative value to the surgeon.
    Knee Surgery Sports Traumatology Arthroscopy 02/2012; · 2.68 Impact Factor
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    ABSTRACT:   In studies concerning the stability of surgical tendon fixation techniques, a large variety of test configurations is found resulting in a broad scatter of results. The goal of this study was to establish a reliable test protocol for the investigation of the stability of repair techniques. At 88 fresh bovine shoulders, four different suture configurations were tested: simple stitches, mattress sutures, modified Mason-Allen configuration and double-row configuration. The difference in response to load cycles with native samples and that after repair was recorded. Bioresorbable anchors were used for tendon fixation, in a second run tendons were affixed to metal plates, and with a third run fixation stability was monitored with a video camera. The double-row technique was the most stable one with the lowest values of compliance at all selected levels of gap formation followed by the mattress suture configuration. The simple stitch configuration and the modified Mason-Allen techniques were the most compliant techniques. By establishing this test protocol, we achieved a very accurate method of measurement (accuracy of 2 μm) with as few external influences as possible. The great advantage is that the proposed protocol allows the measurement of the mechanical quality of the suture fixation without an external device such as calipers.
    Strain 09/2011; 47(5):421 - 429. · 0.92 Impact Factor
  • A. Jäger, T. Bader, K. Hofstetter, J. Eberhardsteiner
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    ABSTRACT: Nanoindentation is a well known tool for identification of mechanical properties at the micrometer scale of materials. When applied to study wood cell walls the commonly used isotropic indentation theory is not applicable. In this study, anisotropic nanoindentation theory was employed for analyzing nanoindentation test results on wood cell walls. The influence of elastic stiffness components, microfibril angle, and cell wall composition on the indentation modulus was studied. The indentation modulus was found to depend on longitudinal, transverse, and shear modulus to a similar extent. A significant influence of the microfibril angle on the indentation modulus was observed and discussed with respect to experimental scatter and sample preparation. It is concluded, that application of anisotropic nanoindentation theory provides a tool for quantitative instead of qualitative investigation of wood cell walls, with the goal of identifying all elastic properties of the transversely isotropic cell wall from nanoindentation tests.
    Composites Part A Applied Science and Manufacturing 06/2011; 42:677-685. · 3.01 Impact Factor
  • Bernhard Pichler, Christian Hellmich, Josef Eberhardsteiner
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    ABSTRACT: Quantification of the strength of geomaterials is often the key to effective solutions to problems in geoengineering. The scales where underlying processes are favorably studied and quantified may largely vary. We here consider two quite distinct cases, related to penetration resistance of gravel under rockfall, and to chemically driven strength growth in sprayed concrete (shotcrete), together with corresponding large-scale applications: rockfall protection of oil pipelines and tunneling according to the New Austrian Tunneling Method.

Publication Stats

467 Citations
100.45 Total Impact Points

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  • 1995–2014
    • Vienna University of Technology
      • Institute of Mechanics of Materials and Structures
      Wien, Vienna, Austria
  • 2012
    • Saint Vincent Hospital
      Worcester, Massachusetts, United States
  • 2010
    • Warsaw University of Technology
      • Faculty of Materials Science and Engineering
      Warsaw, Masovian Voivodeship, Poland