Katalin Bagi

Katalin Bagi
TU Budapest · Department of Structural Mechanics

DSc, DrHabil, PhD

About

67
Publications
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Publications

Publications (67)
Article
Fan vaulting is a magnificent innovation of English Gothic architecture that has been admired since the 14th century. However, how this breathtaking structural form works under mechanical loads (like self-weight and support displacement) is still poorly understood. One of the many interesting open issues is the mechanical role of backfill. This pa...
Article
An interlocking block is a concave polyhedron with non-planar joints connecting the blocks together. The possibility of the fracture within a masonry interlocking block is a major challenge that has remained rather unexplored yet. Different fracture scenarios can be taken into account through considering the crack planes at which the block can be s...
Article
Full-text available
This paper presents a computer aided design tool that analyses the structural feasibility of interlocking assemblages with orthotropic sliding resistance and automatically adjusts the assemblage shape to remove the infeasibility. First, the static problem of limit analysis is extended to the corrugated interfaces. To model different bond patterns a...
Conference Paper
Full-text available
Applications of interlocking blocks improving the sliding resistance of masonry joints have recently been of significant interest to architects and structural engineers. In this framework, several works have studied the load capacity improvement of different joint shapes using various numerical and experimental analyses. However, applications of si...
Article
Full-text available
The characterisation and classification of particle form are typically based on the consideration of the main particle dimensions, for the derivation of which no method has been unanimously accepted or proven to be representative of its morphology or load-bearing capabilities. This study proposes a weighted fabric tensor, named “surface orientation...
Research Proposal
Full-text available
Enrollment deadline: June 26, 2021. https://www.cism.it/en/activities/courses/A2102/ Masonry structures – collections of individual solid blocks with dry or mortared contacts – appear everywhere around us, from architectural heritage through historic or contemporary civilian buildings to traffic infrastructure. The assessment of their structural i...
Article
Full-text available
Increasing interest has recently been devoted to interlocking blocks/interfaces capable to enhance the sliding resistance of masonry joints to external forces. In this framework, this paper deals with the assessment of the torsion-shear capacity of the contact interface between the lock and the main body of an interlocking block, assumed to have a...
Preprint
Full-text available
Increasing interest has recently been devoted to interlocking blocks/interfaces capable to enhance the sliding resistance of masonry joints to external forces. In this framework, this paper deals with the assessment of the torsion-shear capacity of the contact interface between the lock and the main body of an interlocking block, assumed to have a...
Article
Full-text available
Fan vaults, the most spectacular structural form of the English Gothic architecture, has been admired by architect lovers for many centuries. The mechanics of fan vaulting raises several interesting questions, most of which are still unanswered, even though the maintenance and restoration of historic buildings would require the deep understanding h...
Article
Bond patterns influence responses of masonry barrel vaults to mechanical loads. In this research, the discrete element method (DEM) was applied to investigate how bond patterns affect the static load bearing capacity of barrel vaults under vertical loads. The two most widely-used bond patterns (transverse and longitudinal) were studied. Using a com...
Article
Full-text available
The presented research focuses on masonry shells with dry (cohesionless) contacts. In the mechanical analysis of such structures the material is often assumed to have zero resistance to tension. This simplification can be questioned in light of the fact that due to the frictional resistance between masonry layers compressed to each other, significa...
Conference Paper
Full-text available
Discrete element method (DEM) has proved to be an excellent tool for modelling bulk materials. Contrarily to the early stages of these simulations when mainly circular and spherical elements were used, extensive research is going on regarding the application of complex element shapes, e.g. polyhedra. Robust and objective geometry characterisation m...
Conference Paper
Full-text available
The paper presents some of the most interesting results of the author's team achieved in the field of masonry statics in recent years. Investigations were done with computer-simulated experiments using the discrete element method (DEM). The general aim was to reveal how different types of masonry structures respond to static loads. In DEM the struc...
Conference Paper
Full-text available
Masonry shells with no-tension joints can exhibit considerable resistance to hoop tension because of the frictional forces arising between masonry layers due to meridional compression, and this phenomenon can give a considerable extra resistance to the structures. The aim of the study was to quantify this hoop-directional tension resistance in case...
Chapter
Discrete element models have become a major tool for masonry analysis, allowing a suitable representation of its discontinuous nature and marked nonlinear behaviour. The chapter reviews the fundamental assumptions of the main DEM formulations available. It focuses more specifically on the widely used UDEC and 3DEC codes, explaining their relation w...
Thesis
Full-text available
This MSc thesis prepared by Yu Meng at the Department of Structural Mechanics of TU Budapest under the supervision of prof. Katalin Bagi focuses on the mechanics of masonry arches. The load carrying behaviour of different arch geometries was analysed with the three most important computational techniques (3DEC, Archie-M and LimitState:RING) based o...
Article
This paper investigates the influence of construction method (e.g. false skew, helicoidal and logarithmic method) on the mechanical behaviour and load carrying capacity of single span skew masonry arches. Simulations were performed with the three dimensional computational software, based on the Discrete Element Method of analysis. Each stone/brick...
Chapter
Full-text available
The Contact Dynamics method, developed still in the 1980s, was originally applied for granular assemblies because of its efficiency in simulating rapid granular flows or vibration problems of discrete systems. In the oldest models the elements were spherical and perfectly rigid, but later the application of polyhedral and deformable elements also b...
Chapter
Full-text available
“DDA” stands for “Discontinuous Deformation Analysis”, suggesting that the displacement field of the analyzed domain shows abrupt changes on the element boundaries in the model. This chapter introduces the theoretical fundaments of DDA: mechanical characteristics of the elements together with the basic degrees of freedom, contact behavior, the equa...
Article
Full-text available
Stone cantilever staircases are present in case of both new constructions and reconstructions. The aim of the present paper is to understand the mechanical behaviour of these staircases with the help of discrete element simulations, and to compare the calculated behaviour to the estimations given by the existing manual calculation methods. First a...
Conference Paper
Full-text available
A significant portion of the UK's bridge stock is represented by multi-ring brickwork masonry arches. Most of these bridges are well over 100 years old and are supporting traffic loads many times above those originally envisaged. Different materials and methods of construction used in these bridges will influence their strength and stiffness. There...
Article
The problem of determining the minimum thickness of masonry arches has been a challenge to the engineering community through the last two centuries. Although significant work has been undertaken to investigate the minimum thickness of semi-circular and elliptical rectangular arches, no work has been done to investigate the minimum thickness of skew...
Article
Full-text available
This study focuses on domes the ground plan of which, instead of the more common circular shape, is an oval, and aims at finding the minimally necessary uniform wall thickness for domes of different geometries loaded by their selfweight. The discrete element code 3DEC was applied because of its capability of simulating the collapse mechanisms of ma...
Article
Full-text available
The paper presents discrete element simulations of the in-plane horizontal shear of planar walls having different bond patterns. The aim of the analysis was to decide whether the shear resistance could be improved by applying patterns containing vertical bricks. The results show that the presence of vertical bricks increases the shear resistance in...
Article
The magnitude of horizontal reactions under self-weight are analysed for pointed barrel vaults with different eccentricities. The magnitude is expressed as the function of the eccentricity (deviation of the pointed generator curve from the circle). Vaults with fixed supports and with increasing outwards support displacements are considered. An anal...
Article
The role of ribs in the mechanical behavior of masonry cross vaults has been the subject of intense debates since the 19th century. Literature on the subject diverges from considering the ribs as the main load-bearing units which carry the weight of the masonry web, to the opinion that the ribs are merely decorations. This research focused on the s...
Article
Full-text available
Heyman’s Safe Theorem is the theoretical basis for several calculation methods in masonry analysis. According to the theorem, the existence of an internal force system which equilibrates the external loads guarantees that the masonry structure is in a stable equilibrium state, assuming that a few conditions on the material behaviour are satisfied:...
Article
A lunar base structure must provide protection against various hazards such as bombardment by meteorites, radiation, or extreme changes in temperature. A possible structural solution was proposed in the literature. The lunar base, planned to be built in a long, narrow valley with solid rock walls, would consist of three main elements: a masonry vau...
Article
The aim of this study was to investigate the effect of the backfill on the mechanical behavior of a multi-span masonry arch with the help of the discrete element method. After defining the geometry and identifying the mechanical properties of a one-span bridge model according to real experimental results from the literature, we extended the one-spa...
Article
Full-text available
The paper addresses the question of whether the number of particles in a noncemented granular assembly will affect the mechanical characteristics of the assembly: its strength and stiffness. The question is answered by applying the discrete element method to assemblies of different sizes. To isolate the effect of assembly size, apart from the scatt...
Article
Applying a method that is widely known in nonlinear structural mechanics, the paper offers an alternative approach for the jamming analysis of granular assemblies. The main advantage of the proposed approach is that deformable particles with general shapes can be handled with it, in contrast to the previous methods that are restricted to rigid grai...
Article
The aim of this Discussion is to clarify a terminological issue in a previous IJSS paper.
Article
The micromechanical interpretation of strain tensor for granular assemblies has been a subject of considerable scientific interest in recent years. This paper gives an overview on 10 different microstructural strain definitions that can be found in the granular mechanics literature. After a theoretical introduction and comparison, the different ver...
Article
We consider the relative motions of a pair of discrete three-dimensional particles that share a common contact point. The contact interactions are characterized by three independent motions: rigid movement, translational deformation, and rotational (rolling and twisting) deformation. The rigid motions are non-objective but satisfy a weakened object...
Article
A discrete element simulation of a mechanical problem involving granular materials begins with the definition of the geometry of the sample to be analyzed. Since the dynamic sample preparation methods typically used in the practice are very time-consuming, constructive algorithms are becoming increasingly popular. This paper introduces a novel cons...
Article
The poster focuses on the possibilities of numerical modeling of masonry arches. Masonry arches have been built since the beginning of human civilization, and consist of individual solid blocks, often fixed to each other by mortar. The aims of our research are to set up numerical models, which are able to represent the behavior of the different mas...
Article
The paper presents a definition of particle rolling for the interactions of two and three-dimensional particles of arbitrary shape, in case of infinitesimal particle translations and rotations. The definition is based on a purely kinematical analysis, and it is shown to satisfy the objectivity condition.
Article
The paper considers rotations at different scales in granular materials: the rotations of individual particles, the rolling and rigid-rotation of particle pairs, the rotational interactions of a particle within its cluster of neighbors, and the rotation of material regions. Numerical, Discrete Element Method (DEM) simulations on two- and three-dime...
Article
The paper presents a definition of rolling between a pair of two-dimensional or three-dimensional particles with a compliant contact. The definition of rolling movement is based upon the shapes of the objects' surfaces as described with differential geometry. A pseudoinverse of the surface curvatures is used for producing a rolling vector that is t...
Article
Full-text available
The paper presents a definition of particle rolling for the interactions of two and three-dimensional particles of arbitrary shape, in case of infinitesimal particle translations and rotations. The definition is based on a purely kinematical analysis, and it is shown to satisfy the objectivity condition.
Article
This paper discusses possible models for probability distributions of contact force magnitudes in loaded granular media. Many authors have studied such distributions, based on experiments with real particles as well as simulations in 2D and 3D. This has led to various and partly contradicting suggestions for the form of those distributions, which a...
Article
Full-text available
This paper analyses the probability density functions of contact force components corresponding to the principle directions of average stress. A theoretical prediction is derived for the distribution of these components, with the help of maximizing the statistical entropy. Limits of validity of the prediction are analyzed by numerical simulations o...
Article
Full-text available
The paper introduces two possible definitions for microstructural stress in granular assemblies. A stress tensor is derived from direct statical considerations (this stress is always symmetric in the absence of contact moments), and another stress tensor is found by the principle of virtual displacements (the authors show that this stress may be as...
Article
Full-text available
The paper includes a summary of previous work, currently in review, concerning alternative definitions of the relative rotation and rolling between particle pairs. These definitions provide a basis for objective contact mechanisms that include the effects of relative rotational movements as well as the relative translations of the particles at a co...
Article
Full-text available
Particle rotations can have a dominant influence on the behavior of granular materials, particularly in materials with circular or spherical particles. The paper briefly reviews experimental evidence of the magnitude and variability of particle rotations and their effect on a granular material's stiffness and strength. Evidence of rotational patter...
Article
This paper focuses on the discrete expression of stress tensors of assemblies containing discrete particles with volumetric loads acting on them in addition to boundary forces. Instead of the concept of continuum point, a domain containing a finite number of grains is considered. This domain is replaced by a suitably chosen equivalent continuum who...
Article
The paper deals with the theoretical and numerical analysis of granular assemblies. Introduction of the re-interpretation of classical continuum-mechanical state variables is followed by a summary of continua with higher degrees of freedom. Results of numerical experiments are shown to point out that classical continua cannot contain enough informa...
Article
The aim of this paper is to clarify the meaning of the mechanical state variables stress and strain in the case of random granular assemblies. Stress and strain are expressed in terms of local, micro-level variables with the help of two complementary geometrical systems. The two expression show a strong duality which is also analysed in the paper.
Article
On the basis of experimental results a numerical model was elaborated to follow the changes of the microstructure of granular assemblies. The distributions of internal forces and displacements were not possible to determine so we tried to characterize the assemblies with the angles of neighbouring contacts.
Article
This paper introduces a quasi-static numerical model based on the displacement method and on the compilation of global equilibrium equations of granular assemblies. The model is able to describe large displacements, rearrangements and local instabilities.
Article
A quasi-static numerical algorithm is introduced for the analysis of quasi-static state-changing processes of granular materials. The paper presents the application possibilities of the model. Both sand-like and cemented materials can be analysed; rearrangements, instabilities, local slips, crack opening, etc., can easily be followed.
Article
We have developed a quasi-static numerical algorythm to evaluate the different suggested variables for granular materials. With the help of numerical shear and compression tests we measured the changing of the variables suggested by Satake, and Cundall & Strack. We found that only a few of them are characteristic to the internal behaviour of the as...
Article
A numerical method has been developed for the analysis of the internal behaviour of granular materials. State-changing processes of microstructure can be followed; the final aim is to find state variables that can reliably describe these processes.
Article
A discrete model made for the analysis of state-changing processes of granular assemblies is introduced here. Our numerical experiments can help in the analysis of some theoretically suggested variables that could be used later in the macro-level description of the behaviour of granular materials.
Article
Full-text available
The paper considers possible frameworks for the transition from the micro-scale behavior of granular materials to the mod- eling of larger scale problems. The paper reviews direct experimental evidence that granular materials deviate from classical continuum assumptions at several length scales. Granular materials also exhibit other behaviors that...
Article
Full-text available
Our paper focuses on the uniaxial compression failure strength of granular rocks. The results of laboratory tests usually show a rather high scatter that has mostly been explained by the small random errors when doing the experiments. Our aim was to supervise this problem from microstructural point of view and to point out that the geometrical rand...

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Projects

Projects (2)
Project
https://www.cism.it/en/activities/courses/A2102/ registration deadline: 26 June 2021 Masonry structures – collections of individual solid blocks with dry or mortared contacts – appear everywhere around us, from architectural heritage through historic or contemporary civilian buildings to traffic infrastructure. The assessment of their structural integrity poses serious challenges: due to their discrete built-up, usual continuum-based calculation methods are often incapable to reflect the mechanical behavior. In cases when the failure is caused by some kind of a local effect (cracks opening up between voussoirs, individual blocks sliding out etc.) the mechanics of the problem may better be captured by methods that consider the structure as a collection of discrete bodies. Such methods are available in a wide variety today. The aim of the course is to give a detailed introduction to their theoretical fundaments, advantages and preferable fields of application, but also calling the attention to their limitations and disadvantages so that the participants of the course would build up a critical view of the choices they have when attacking a masonry mechanics problem. An explicit aim of the course is to give a sound basis for the participants to become able to develop their own methods, inspired either by classical graphical statics, or by any modern technique they find promising. The course will focus on four main topics: 1) Computerized graphical statics methods Graphical statics seemed to lose practical importance in the 2nd half of the XXth century when continuum-based numerical techniques and Limit State Analysis methods became widely applied in computerized manners. However, the recent decades brought a renaissance to the application of graphical statics in masonry analysis: powerful computer codes have been developed part of which are commercially available and part of which can be found as research tools. 2) Discrete element methods DEM was born at the end of the 1960ies as an alternative to FEM. DEM considers the simulated material or structure not as a continuum but as a collection of separate bodies being able to detach, slide, partly or completely separate, and form new contacts when large displacements may lead to the rearrangement of contact topology. Possibilities to partial cracking and sliding makes DEM particularly advantageous for masonry failure problems. 3) Blocky models The main drawback of DEM is that the analysis of whether new contacts are born in the system, simulations can be very computationally expensive. To avoid this, different blocky models have been suggested recently for problems when rearrangements of the topology are not expected, but the discrete built-up of the system is relevant (e.g. formation of partial cracks). These novel methods are considered as being in-between FEM and DEM. 4) Discrete dynamics Masonry structures are sensitive to earthquakes: seismic analysis is a crucial issue in masonry mechanics. Damping and contact sliding are significant in their energy dissipation and in the ability to adjust to ground displacements. Hence, special lectures will be devoted to the dynamics of masonry structures. In particular, lectures will focus on damping and large displacement dynamics which characterize the dynamic collapse of masonry structures. Targeted audience: young researchers (including PhD students); engineers interested in high-level computational tools for masonry analysis. More info: https://www.cism.it/en/activities/courses/A2102/
Project
The goal of this project is to compare and develop quantification methods for the geometrical properties of grains (e.g. size, elongation, surface roughness), which can be used to study the effect of grain shape on the mechanical behaviour of assemblies. These parameters can be also applied to validate the geometry of non-spherical particle assemblies in discrete element (DEM) simulations. The project also involves experiments and simulations on the effect of grain shape on the mechanical behaviour of granular assemblies.