Bernhard Pichler

TU Wien | TU Wien · Institute of Mechanics of Materials and Structures

Deflection modes relevant for plates with rigidly supported edges are commonly used as kind of “approximation” for the deformation behavior of plates which are freely swimming on an elastic foundation. However, this approach entails systematic errors at the boundaries. As a remedy to this problem, we here rigorously derive a theory for elastically...

Transfer relations, representing analytical solutions of the linear theory of slender circular arches, have facilitated structural analysis of segmented tunnel linings. This is the motivation to apply such relations to two examples of circular arch bridges in which the bridge deck is held from the arch by equally spaced hangers. First, the number o...

Structural analysis of segmented tunnel rings is challenging, because displacement discontinuities and relative rotation angles develop at segment-to-segment interfaces. To meet this challenge, a hybrid method was recently developed by Zhang et al. (2017). It uses the known external loading and measured interfacial discontinuities as input for stru...

Reinforced concrete hinges, subjected to eccentric compression, are failing in a ductile fashion (Schlappal et al. 2017). Three-dimensional Finite Element simulations are prime candidates for a more detailed analysis of this interesting structural behavior. Such nonlinear simulations, however, typically require pocedures for updating of the underly...

The title of this work represents a figurative counterpart of bridging the topographical gap between Hongkong and Macao. Presently under construction, the bridge that connects these two cities at opposite sides of the mouth of the Pearl River is interrupted by a submersed tunnel, which is the actual research object of this paper. By means of four d...

Chloride ingress into concrete is a major cause for material degradation, such as cracking due to corrosion-induced steel reinforcement expansion. Corresponding transport processes encompass diffusion, convection, and migration, and their mathematical quantification as a function of the concrete composition remains an unrevealed enigma. Approaching...

Multiscale structural “hybrid analysis” is proposed to analyze a real-scale exper- iment of a displacement-monitored segmented tunnel ring. Material modeling of concrete starts at the molecular scale of calcium-silicate-hydrates. Their elastic stiffness and fracture energy are upscaled to the material level of concrete, where the tensile strength o...

Rubber friction on ice is studied both experimentally and theoretically. The friction tests involve three different rubber tread compounds and four ice surfaces exhibiting different roughness characteristics. Tests are carried out at four different ambient air temperatures ranging from \(-5\) to \(-13\,^{\circ }\hbox {C}\), under three different no...

Concrete hinges experience a renaissance, because the past decades have provided practical evidence that they are durable structural elements, but the functionality of concrete hinges remains to a considerable extent an enigma. This provides the motivation to gain further insight into the structural behavior of concrete hinges, based on nowadays-av...

Cement pastes are highly creep active materials at early ages. We here characterize both the elastic stiffness and the creep properties of ordinary Portland cement pastes conditioned at 20 °C. Three different compositions are investigated, defined in terms of initial water-to-cement mass ratios amounting to 0.42, 0.45, and 0.50, respectively. Imple...

Creep functions are often represented by "rheological models" consisting of springs and dashpots, while the actual microscopic origins of creep, such as micro-sliding along interfaces, has only recently been explicitly considered in a continuum mechanics framework. The question arises whether formal analogies between the former and the latter can b...

Whereas the companion paper provided a micromechanical explanation of the spring and dashpot parameters occurring in the rheological models of the Kelvin-Voigt and Maxwell type, we here extend this discussion toward rheological chain models. Therefore, the considered micromechanical system is extended from one interface phase to N interface phases...

Cementitious materials are particularly creep active at early ages. We here perform an ageing creep test on a cement paste sample exhibiting an initial water-tocement mass ratio amounting to w/c = 0.50. The sample is conditioned to 20°C. The creep test is started 24 hours after production and runs for 48 hours. The loading amounts to 15% of the uni...

Nanoindentation testing suggests that creep of hydration products is the microscopic reason for macroscopic creep of cementitious materials. This is supported by a multiscale creep model which explains aging creep of young concretes as the consequence of universal creep of hydration products (Scheiner and Hellmich, 2009), whereby the latter is desc...

Matrix-inclusion composites are known to exhibit interaction among the inclusions. When it comes to the special case of inclusions in form of flat interfaces, interaction among interfaces would be clearly expected, but the two-dimensional nature of interfaces implies quite surprising interaction properties. This is the motivation to analyze how int...

The chemical hardening reaction between cement and water results in the evolution of macroscopic mechanical properties of cementitious materials at early ages. We here provide experimental insight into the evolution of short-term creep properties of cement pastes and mortars with different compositions in terms of (i) the initial water-to-cement ma...

The stiffness evolution of binder ‘cement paste’ is triggering the stiffness of concrete. In the engineering practice, concrete formworks are typically removed 24 h after production. This underlines that knowledge on mechanical properties of cementitious materials during the second, third and fourth day after production is of high relevance for the...

From the biological/chemical perspective, interface concepts related to the cell surface/synthetic biomaterial interface and the extracellular matrix/biomolecule interface have wide applications in medical and biological technologies. Interfaces also play a significant role in determining structural integrity and mechanical creep and strength prope...

Crack initiation in concrete, represents the elastic limit of the material, typically starting in the 15 microns thick interfacial transition zones (ITZs) around aggregates. Recently, two possible modes for crack initiation have been identified from inspection of post-failure concrete fragments: clean separation of aggregates from ITZs and ITZ crac...

Eine spannende und wichtige Klasse von Ingenieurbauwerken sind unterirdische Tragwerke. Prof. Josef Eberhardsteiner berichtete über das „Tragverhalten junger Tunnelkalottenschalen aus Spritzbeton“. Dafür gibt es neue Modellierungsansätze, die sehr anspruchsvoll sind.

It is fairly well accepted that the «lubricant effect» of water or other fluids is a key to the creep behavior of a large range of bio- and geomaterials. However, a more precise theoretical assessment is found, at best, rarely. As a remedy, we start here from 2D viscous interfaces where shear tractions trigger in plane displacement discontinuity ra...

Concrete aggregates are covered by 15-microns-thick interfacial transition zones (ITZs) exhibiting larger porosity, but smaller stiffness and strength than the adjacent bulk cement paste. This renders the immediate vicinities of the aggregates' surfaces as the weakest links within the microstructure of concrete. Onset of cracking, representing the...

In the 1930s, Freyssinet presented a model describing that the strength of cement paste decreases with increasing capillary porosity. He proposed that uniaxial compressive strength of cement pastes is proportional to a volume quotient which is nowadays referred to as «gel-space ratio». In the 1970s, Fagerlund found out that capillary porosity is no...

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 ave...

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 valida...

Based on an advanced micromechanics-based nonlinear creep model for shotcrete and thin shell kinematics, measured displacement data are first converted into in-plane stress fields throughout a shotcrete tunnel shell driven according to the New Austrian Tunneling Method (NATM). Subsequently, the partial differential equations for local force equilib...

It is generally agreed upon that fluids may play a major role in the creep behavior of materials comprising heterogeneous microstructures and fluid-filled porosity at small length scales. In more detail, nanoconfined fluid-filled interfaces are typically considered to act as a lubricant, once electrically charged solid surfaces start to glide along...

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...

Displacement measurement‐based estimations of loads and utilization degrees in shotcrete tunnel shells as part of the New Austrian Tunneling Method (NATM), have become standard tools in tunnel practice; their quality, however, may crucially depend on the knowledge of the actual shotcrete composition after spraying. To shed light on this issue, we h...

In this work, multi-scale models for wood, asphalt concrete, and cementitious materials are presented. Leading, on the one hand, to a better understanding of the complex behaviour of these materials and, on the other hand, providing accurate sets of macroscopic properties as input for structural simulation tools. In the following, the key feature o...

It is well known from experiments that the uniaxial compressive strength of cementitious materials depends linearly on the degree of hydration, once a critical hydration degree has been surpassed. It is less known about the microstructural material characteristics which drive this dependence, nor about the nature of the hydration degree–strength re...

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 gr...

Knowledge of the stress state in shotcrete tunnel shells is a necessary requirement to assess the safety of these structures. Estimation of these stresses from measured 3D tunnel shell displacement requires material models for shotcrete. Preferably such models should be able to deal with on-site adaptations of the water-cement and aggregate-cement...

The success of the New Austrian Tunneling Method (NATM) mainly lies in the careful monitoring of the deformation states of freshly excavated cross sections, the boundaries of which are sealed through a thin shell of shotcrete. While undergoing remarkable deformation, this thin shell secures the inner cavity from loosening ground, when the (huge) gr...

The analysis of microheterogeneous materials exhibiting eigenstressed and/or eigenstrained phases requires an estimation of eigenstrain influence tensors. Within the framework of continuum micromechanics, we here derive these tensors from extended Eshelby-Laws matrix-inclusion problems, considering, as a new feature, an auxiliary matrix eigenstress...

Two safety topics in pipeline engineering are treated in this paper: (i) rockfall onto gravel-buried steel pipes and (ii) protection of the outer anti-corrosion coating of soil-covered steel pipelines. In both cases non-linear elasto-plastic Finite Element analyses provide insight into the structural behavior, as needed for the design of effective...

Point-wise optical measurements of 3D displacement vectors over time are a key input for monitoring shotcrete tunnel shells during construction according to the New Austrian Tunnelling Method (NATM). Aiming at estimation of the stresses prevailing in the highly loaded, hydrating material, we here deal with two different interpolation strategies for...

Tensile microcracking of quasi-brittle materials is studied by means of micromechanics, based on (i) an elasto-damaging cohesive zone model accounting for cohesive softening and (ii) a dilute distribution of non-interacting microcracks of uniform orientation and size. Considering virgin microcracks (initially without cohesive zones), macroscopic te...

Multiscale analysis is a stepwise procedure to obtain macro-scale material laws, directly amenable to structural analysis, based on information from finer scales. An essential ingredient of this mode of analysis is mathematical homogenization of heterogeneous materials at these scales. The purpose of this paper is to demonstrate the potential of mu...

Mechanics of Materials and Structures has become a popular new name of former Institutes for Strength of Materials and/or Structural Analysis at European Universities of Technology. This designation stands for a scientific program aimed at a symbiosis of material and structural mechanics. The adjective “computational” refers to the algorithmic comp...

Early-age stiffness and strength evolution of cement paste is studied in the framework of continuum micromechanics. Based on the self-consistent scheme, elastic and strength properties are upscaled from the scale of several micrometers up to the scale of several hundreds or thousands of micrometers. Four material phases are considered: clinker, hyd...

Synchrotron radiation micro-computed tomography (SRmuCT) revealed the microstructure of a CEL2 glass-ceramic scaffold with macropores of several hundred microns characteristic length, in terms of the voxel-by-voxel 3D distribution of the attenuation coefficients throughout the scanned space. The probability density function of all attenuation coeff...

Synchrotron radiation micro-computed tomography (SRμCT) revealed the microstructure of a CEL2 glass–ceramic scaffold with macropores of several hundred microns characteristic length, in terms of the voxel-by-voxel 3D distribution of the attenuation coefficients throughout the scanned space. The probability density function of all attenuation coeffi...

Knowledge of the stresses in shotcrete tunnel shells is of great importance for assessing their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models allowing for variation of the water—cement and the aggregate—cement ratio. This is the motivation for emp...

Drying of deformable porous media results in their shrinkage, and it may cause cracking provided that shrinkage deformations are hindered by kinematic constraints. Herein, we focus on slow drying of an initially water-saturated sample of a microheterogeneous poroelastic material damaged by parallel mesocracks. The cracking risk is analyzed by means...

Drying of deformable porous media results in their shrinkage, and it may cause cracking provided that shrinkage deformations are hindered by kinematic constraints. This is the motivation to develop a thermodynamics-based microporoelasticity model for the assessment of cracking risk in partially saturated porous geomaterials. The study refers to 3D...

This paper deals with the dissipation associated with quasistatic microcracking of brittle materials exhibiting softening behavior. For this purpose an elastodamaging cohesive zone model is used, in which cohesive tractions decrease (during crack propagation) with increasing displacement discontinuities. Constant cohesive tractions are included in...

We study the structural behavior of a rock mass made of argillite, from which a cylindrical underground opening was excavated. Prescribing that the relative humidity of the air within the gallery is < 100% causes the surrounding clay-containing, sedimentary rock to desaturate and to dry progressively. Because near-surface layers dry faster than the...

Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which may preferentially consider variations in the water–cement and aggregate–cement ratios. Therefore,...

In view of extending classical micromechanics of poroelasticity to the non-saturated regime, one has to deal with different pore stresses which may be affected by the size and the shape of the pores. Introducing the macrostrain and these pore stresses as loading parameters, the macrostress of a representative volume element of a porous material can...

Increasing rockfall activity in the European Alps raises the need for designing systems protecting Alpine infrastructure. So far, layout of rockfall protection layers was carried out in a quasi-deterministic manner. This paper is concerned with the extension towards a semi-probabilistic design of the thickness of gravel layers covering steel pipeli...

Consideration of cohesive microcracks in continuum micromechanics is a challenging task since a lot of applications (such as, e.g., estimation of the stiffness of a microcracked solid) require a priori knowledge of the size of the cohesive zone. The latter, however, can be determined analytically only for the special case of Barenblatt–Dugdale crac...

Strain-softening is the decline in stress at increasing strain. Although microcracking is a commonly accepted reason for strain-softening, the majority of theoretical developments involve macroscopic damage evolution laws. To improve this situation, we propose a micromechanics-based damage evolution law by combining (i) the propagation criterion fo...

We here investigate potentials and limitations of Griffith’s energy release rate criterion to describe effective stress-strain behavior of brittle materials damaged by mode I type propagating microcracks. For this purpose stiffness estimates for representative volume elements (RVEs) of a microcracked material (based on continuum micromechanics) are...

Herein, we re-analyze direct tension experiments on concrete by means of recent developments in continuum micromechanics. This way, insight into damage propagation within the strain localization zone (fracture process zone) in concrete under uniaxial tension is obtained, highlighting potentials and limitations of continuum micromechanics as the bas...

Oil and gas pipelines covered with a mixture of sandy gravel and square-edged stones are subjected to abrasive shear loading steming from temperature-induced displacements of the pipeline in longitudinal direction. This requires wear protection of the outer anti-corrosion film of such pipes. In order to assess appropriate means for protection, adve...

Increasing rockfall activity in the European Alps has raised the need for designing protection systems for Alpine infrastructure. This paper is concerned with protection of steel pipelines by a gravel overburden of height H. Rockfall-induced loading of such pipes is estimated by means of a three-dimensional, quasi-static, elasto-plastic finite-elem...

The experimentally observed stress decline in displacement-controlled exper- iments is referred to as strain-softening. Although microcracking is a commonly accepted reason for strain softening, the majority of theoretical developments is purely macroscopic. To overcome inherent shortcomings of this approach, we propose a micromechanics-based damag...

This article deals with the assessment of two different protection systems for buried steel pipelines which are endangered by rockfall. First, a gravel-based protection system (GBPS) is investigated, that is, a pipeline buried in sandy gravel is considered. To assess the load-carrying behavior of this structure when subjected to rockfall, a finite...

Layers of gravel represent an energy-absorbing system for structures subjected to rockfall. To support the design of such structures, relations between the penetration depth, the impact duration, and the impact force, respectively, and the rock boulder mass, the height of fall, and the indentation resistance of the gravel are presented. Knowledge a...

This paper deals with rockfall-endangered pipelines made of steel, which are protected by an overburden con- sisting of densified wide-range-grained gravel. In order to define the minimum adequate height of the overbur- den, the load-carrying behavior of the hit structure is analyzed. For this purpose, the indentation resistance of gravel is identi...

In this paper, a parameter identification (PI) method for determination of unknown model parameters in geotechnical engineering is proposed. It is based on measurement data provided by the construction site. Model parameters for finite element (FE) analyses are identified such that the results of these calculations agree with the available measurem...

Constitutive models for structural analyses contain material parameters. Usually not all of them can be determined a priori with sufficient accuracy. They must be set such that numerical results agree with available measurements as well as possible. Hence, an inverse problem must be solved. In order to keep the number of the required numerical calc...

A parameter identification (PI) method for determination of unknown model parameters in tunnelling is presented. The PI method is based on measurement data provided by the construction site. Model parameters for finite element (FE) analyses are identified such that the results of these calculations meet the available measurements as well as possibl...

The three topics selected for this paper are taken from structural engineering with special emphasis on civil engineering. The tool for numerical solutions of the respective engineering problems is the finite element method. The first topic is structural stability. From a design-orientated viewpoint, it is frequently not necessary to perform a full...

In order to avoid a fully nonlinear analysis to obtain stability limits on nonlinear load-displacement paths, linear eigenvalue problems may be used to compute estimates of such limits. In the paper an asymptotic approach for assessment of the errors resulting from such estimates is presented. Based on the consistent linearization of the geometrica...

splitting. Summary. In unconne d and conne d uniaxial compression experiments on brittle ma- terials { performed with proper lubrication of the interfaces between the load plates and the specimen { microcracks grow mainly in the direction of the governing principal com- pressive stress. This failure mechanisms is referred to as axial splitting. To...

Herein, we study the evolution of both early-age stiffness a nd early-age compressive strength of shotcrete, in the framework of continuum microm echanics. Minimizing the number of necessary material properties, micromechanics-based m odeling of shotcrete is based on non- changing ('universal') mechanical properties of the shotc rete constituents (...