János Lógó

János Lógó
Budapest University of Technology and Economics · Department of Structural Mechanics

PhD

About

92
Publications
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652
Citations

Publications

Publications (92)
Article
Full-text available
This paper presents elasto-plastic limit analysis of reliability-based geometrically nonlinear topology optimization. For this purpose, by reason of uncertainties the volume fraction is considered randomly during optimization. Thus reliability-based design has been considered for solving the problems. To perform reliability-based topology optimizat...
Article
Full-text available
This study is devoted to a novel method for topology optimization of elastoplastic structures subjected to stress constraints. It should be noted that in spite of the classical solutions of the different type of elastoplastic topology problems are more than 70 years old, the integration of the Prandtl-Reuss constitutive equations into the topology...
Article
The paper deals with a novel approach to development of optimality criteria based finite element code for topology optimization of elasto-plastic structures. The novelty of this work is related to the concept of function object called functor and its application to efficient FE code development. First, the general problem of topology optimization u...
Chapter
Optimal topologies obtained for structures subjected to deterministic loading can be sensitive to loading variations in terms of both magnitude and direction. Therefore, in this study we consider problem of topology optimization for structures subjected to probabilistic loading. The proposed method applies basic findings from probability theory, wh...
Article
A numerical investigation is performed addressing the optimal design of stiff structures accounting for uncertainty in loading amplitudes. A minimum volume problem is endowed with a stochastic compliance constraint handling normal distributions and solved adopting mathematical programming. The formulation, originally conceived for a single load cas...
Article
There is an additional new fact that topology optimization has started its career more than hundred years ago by Maxwell and only a few years later by Michell. The classical solutions of the different type of plate or shell problems can be followed by the works of Mroz, Prager and Shield. This paper overviews these almost forgotten results. In addi...
Article
The subject of the paper is to investigate a new way for avoiding the development of checkerboard patterns in structural topology optimization, using an additional in-plane rotational freedom. The efficiency of a few, from the many existing formulations, with differing complexity are put into comparison, such as the standard 4 noded bilinear elemen...
Article
Full-text available
The aim of this study is to compare two available numerical tools for solving of partial differential equations for the optimal design of structures. In the past years numerous methods were developed for topology optimization, from these we have adopted the optimality criteria (OC) approach. The main idea is that we state the optimal conditions, th...
Conference Paper
Full-text available
This paper deals with the causes and the development of weak storey mechanisms in concentrically braced frames subjected to seismic action. In order to investigate this phenomenon, different braced frames were designed in accordance with Eurocode provisions. The design parameters and the obtained structures are presented in the paper. Later the res...
Conference Paper
Full-text available
This article deals with concentrically braced frames that are prone to exhibit weak storey behaviour in the case of a seismic event. The introduction of the key features of seismic design of braced frames according to Eurocode 8 is followed by the description of an alternative new redesign method that aims to prevent the occurrence of weak stories....
Article
The plated structures are one of the most frequently used engineering structures. The object of this research work is the optimal design of curved folded plates. This work is an ongoing investigation. There are various solution methods to analyze this type of structures. Here the finite strip method is used. At first single load condition is consid...
Article
The application of a vertical truss as the load bearing structure for horizontal loads is a common and widespread practice in high-rise steel buildings. The bracing of one or two bays of a frame provides a large lateral stiffness and load bearing capacity. One possible brace arrangement is the concentric bracing of the frame. Following usual capaci...
Article
Full-text available
The plated structures are one of the most frequently used engineering structures. The object of this research work is the optimal design of curved folded plates. This work is an ongoing investigation. There are various solution methods to analyze this type of structures. Here the finite strip method is used. At first single load condition is consid...
Article
The loading uncertainties can be expressed by the stochastic nature of any part of the load determination. If any information is probabilistic among the three independent data of the load determination (the magnitude, the line of action and/or the point of application) a more precise design requires to elaborate a probabilistic method. This goal ca...
Article
Full-text available
This paper deals with the causes and the development of weak storey mechanisms in concentrically braced frames subjected to seismic action. In order to investigate this phenomenon, different braced frames were designed in accordance with Eurocode provisions. The design parameters and the obtained structures are presented in the paper Later the resu...
Conference Paper
Loading uncertainties can be expressed by the stochastic nature of any part of the load determination. If any information is probabilistic amongst the three independent data items specifying the loadings (the magnitude, the line of action and the point application) a more precise design requires a probabilistic method to complete the design procedu...
Conference Paper
To describe the load three independent data are necessary: the magnitude, the line of action and the point of application. If any part among these data contains uncertain information the more precise design requires a probabilistic method to elaborate the design procedure. Here a new type of probabilistic optimal topology design method is elaborate...
Article
In this paper a new type of probabilistic optimal topology design method is elaborated for continuum type of structures where the points of application of the loads are given randomly. In the proposed probabilistic topology optimization method the minimum penalized weight design of the discretized structure is subjected to compliance constraint and...
Article
Full-text available
This paper includes description of reliability based design optimization of elasto-plastic skeletal structures under multi-parameter static loading. Presented approach is based on the assumption that the complementary strain energy of the residual forces is considered as an overall measure of the plastic performance for plastic shakedown analysis a...
Article
Full-text available
The aim of this paper is to present and investigate softening and hardening constitutive models derived from the general isotropic work softening and hardening hypothesis and to show their application to the step-by-step analysis of linearly elastic-perfectly plastic softening or hardening skeletal structures (trusses, beams, frames). A quasi-stati...
Article
Full-text available
The aim of this paper is to create new type of plastic limit design procedures where the influence of the limited load carrying capacity of the beam-to-column connections of elasto-plastic steel (or composite) frames under multi-parameter static loading and probabilistically given conditions are taken into consideration. In addition to the plastic...
Article
Full-text available
A new type of probabilistic optimal topology design method is elaborated where the points of application of the loads are given randomly. In the proposed probabilistic topology optimization method the minimum penalized weight design of the structure is subjected to compliance constraint and side constraints. By the use of an appropriate approximati...
Article
Full-text available
The aim of this paper is to take into consideration the influence of the limited load carrying capacity of the connections on the plastic limit state of elasto-plastic steel (or composite) framed structures under multi-parameter stochastic loading and probabilistically given conditions. In addition to the plastic limit design to control the plastic...
Conference Paper
A new type of probabilistic optimal topology design method is detailed here, where the points of application of the loads are given randomly. In the proposed probabilistic topology optimization method the minimum penalized weight design of the structure is subjected to compliance constraint and side constraints. The compliance expression is a proba...
Article
Full-text available
In this paper a numerical study is presented for the effect of the settings of the suspension parameters of a road vehicle for the ride comfort. The chassis of the IK GMC midibus model is investigated as an example. The suspension parameters are represented by hard springs and dampers. By the appropriate choice of the suspension parameters it can b...
Conference Paper
Full-text available
En el presente trabajo se analiza la frecuencia de experimentación y consumo de drogas en alumnos de escuelas medias de Córdoba, Argentina, en relación a variables socio-demográficas. El estudio de carácter analítico se basó en el registro de la Secretaría de Programación para la Prevención de la Drogadicción y la Lucha contra el Narcotráfico. El p...
Article
In the proposed probabilistic topology optimization method, the minimum penalized weight design of the structure is subjected to probabilistic compliance and side constraints. The calculation of the compliance value is based on the assumption that the magnitude of the loads has uncertainties so that their joint normal distribution functions, mean v...
Article
The main structural elements of steel framed multi–storey structures are the columns, the beams and their connectionsmagenta, which can be considered rigid, pinned or semi–rigid. The aim of this paper is to analyze the effect of the semi–rigid connections on the limit analysis of steel structures under multi–parameter static loading where to contro...
Chapter
The aim of this paper is to study the influence of the semi-rigid connections on the plastic behaviour of elasto-plastic steel frames subjected to dead load and quasi-static working loads. In the presented methods the static theorem of plastic limit analysis and the static theorem of shakedown analysis are applied and to control the plastic deforma...
Conference Paper
The aim of this paper is to analyze the influence of the limited load carrying capacity of the connections on the plastic limit state and shakedown of elasto-plastic steel (or composite) framed structures under multi-parameter static loading and probabilistically given residual energy condition. In addition to the limit analysis and shakedown, to c...
Article
The main structural elements of steel framed multi-storey structures are the columns, the beams and their connections. The assumption has been widely applied in the past that the connections are either rigid or pinned. The actual behaviour of the connections is however somewhere between these limits, they are semi-rigid. The aim of this paper is to...
Article
The aim of this paper is to introduce a new type of stochastic optimal topology design method where the loads are given randomly. The standard stochastic mathematical programming problem is based on penalized minimum weight design procedure subjected to a probabilistic compliance constraint due to the loading uncertainties. If the probability of th...
Article
A new approach is presented for the design of structures where the solution of the boundary value problem is approximated by an infinite function series of the state variables expressed in terms of time. Space discretization is used, but the state variables, ordered to the nodes, are continuous functions of time. In spite of a direct mathematical p...
Article
Full-text available
The aim of this research is to introduce a new type of stochastic optimal topology design method with iterative solution technique. The paper presents stochastic topology design procedure and compares the achieved results with optimal obtained topologies on deterministic way. The standard mathematical programming problem is based on a minimum volum...
Article
When in the design of structures extreme loadings such as short time, high intensity dynamic pressure (explosion), impact or earthquake have to be taken into consideration then, except for special cases, the plastic reserves of the material can be utilized, but the development of excessive plastic deformations, residual displacements and the collap...
Conference Paper
Full-text available
Various types of benchmark examples for optimal structural topologies are critically examined and an extensive literature survey of existing exact analytical solutions presented. New classes of analytical solutions, including some popular benchmark problems, are illustrated with examples. Finally, quality control methods for examining the validity,...
Article
Full-text available
This note deals with topological optimization of structures in which some members or elements of given cross-section exist prior to design and new members are to be added to the system. Existing members are costless, but new members and additions to the cross-section of existing members have a non-zero cost. The added weight is minimized for given...
Chapter
Full-text available
The aim of this paper is to discuss some issues of pivotal importance in topology optimization, which receive inadequate attention in the literature.
Conference Paper
The paper discusses new classes of optimal truss topologies, which can be used as benchmarks for testing the validity and convergence of numerical topology optimization methods.
Conference Paper
The aim of this research is to introduce a new type of stochastic optimal topology design method. The paper presents topology design procedure and compares the achieved results with optimal topologies obtained on deterministic way. The standard mathematical programming problem is based on a minimum volume design procedure subjected to a compliance...
Conference Paper
The aim of this research is to introduce a new type of stochastic optimal topology design method. The paper presents topology design procedure which is formed by the use of loading uncertainties and compares the achieved results with optimal topologies obtained on deterministic way. The standard mathematical programming problem is based on a minimu...
Article
Optimal design with thousands of variables is a great challenge in engineering calculations. In this paper beside the short history of optimality criteria methods, a solution technique is introduced for the topology optimization of elastic disks under single parametric static loading. Different boundary conditions and thousands of design variables...
Article
The layout optimization method of rigid-plastic structures (plates, shells, frames, trusses) is based on the assumption that the high intensity, short-time dynamic pressure can be replaced by impulsive loading represented by an initial velocity field. The concept of porous material is used where the material distribution is described by the densiti...
Article
Full-text available
The structural design problem is solved in case of time-dependent loading. The state variables are given in function space, where the Fritz-John theorem is not proved. Approximating the functions by generalized Fourier series, the coefficients become unknowns. Transforming the problem into Banach space, where the Fritz-John theorem is proved, the p...
Article
A shakedown analysis and optimum shakedown design of elasto-plastic trusses under multi-parameter static loading are presented. To control the plastic behaviour of the truss, bounds on the complementary strain energy of the residual forces and on the residual displacements are applied and for the bars under compression critical stresses updated dur...
Article
A design method is presented for layout optimization of linearly elastic–perfectly plastic disks subjected to multiparameter loading. The method is based on the static theorem of shakedown analysis and on the concept of porous material, where the material distribution of the discretized structure is described by the densities of the finite elements...
Article
In the paper, the layout optimization of rigid-plastic disks is presented. The method is based on a model where a disk is subdivided into rectangular elements interconnected by normal and shear forces along their edges. Using this model statically admissible stress fields are constructed and the static theorem of limit analysis is applied. Followin...
Article
Full-text available
A new approach is presented for the analysis of structures with time-dependent loading based on mathematical programming in the function space L 2 . The solution occurred in the vector space. In this paper the computational model of the structures with damping is detailed by the use of internal variables. The energy dissipation is taken into accoun...
Article
In this paper a design method for the optimal strengthening of trusses is presented. Trusses with given configuration composed of linearly elastic-perfectly plastic material are considered and it is assumed that because of the increase or change of the loads their strength and/or stiffness is not satisfactory. The problem is to strengthen the truss...
Article
Full-text available
In this paper two discrete optimization methods are presented for the minimum volume design of elasto-plastic trusses with given geometry. The design is based on given sets of discrete cross-sectional sizes. Both methods enable the use of the plastic reserve of the truss; the plastic deformations, however, are controlled by compliance constraints o...
Article
Optimal plastic design methods of discretized bar structures are presented where the objective function is the volume of the structure and the permanent deformations are controlled by introducing a constraint on the complementary strain energy of the residual internal forces. Single- and multiparameter loadings are considered and in the latter case...
Article
In the analysis of the problem the beam is modelled by hinge elements connected together by rigid bars while the foundation is replaced by spring elements supporting the hinges. The nonlinear behaviour of the beam and the foundation is described by specially formulated bilinear material models. The characteristics of these models are considered to...
Article
Trusses composed of bars with specially formulated bilinear force-deformation characteristics proposed by Lógó and Taylor are treated. Mixed extremum principles are derived, based on potential and complementary potential energy, to form the basis for a load history analysis of trusses. Through the choice of appropriate parameters of force-deformati...
Article
Mathematical modelling processes are computed by the path following method from the literature. A new approximation is presented using parametrical optimization. The problems are solved as nonlinear programming problems by converting the problem from the function space into the 2 space.
Article
A mixed variational principle based on a bilinear material model and on complementary potential energy is applied to the analysis of plane problems. Two discrete models are used to the construction of the fundamental equations. The first model consists of rigid rectangular panels connected along the edges by springs acting in tension, compression a...
Article
In general, the mechanical models are described by different type of differential equations. In the approach presented here the unconstrained optimization problem that derives from the boundary problem is decomposed into a pair of constrained optimization problems. In this paper the presented models concerning the stress-limited elasto-plastic stat...
Article
An extremum principle is presented for structural analysis problems expressed in mixed (stress and deformation) form. The structural model, exemplified for trussed structures, has each member composed of elements coupled in parallel. This type of formulation is convenient for the analysis of systems made up at least partially of materials with stre...
Article
The paper deals with reinforced concrete beams and frames subjected to short-time, high intensity dynamic pressure. The shape and geometry of the structure and the layout of the longitudinal reinforcement are given and the areas of reinforcement are design variables. The determination of the plastic displacements and deformations caused by pressure...
Chapter
The analysis of viscous or viscoelastic structures has to be based on suitable mathematical and mechanical backgrounds. Regarding mathematics, there are two main directions of the solution. One is describing the viscous system by several superposition integrals and the other one is using the Laplace’s transformation. The advantages and disadvantage...
Article
Linearly elastic-perfectly plastic bar structures constructed of prismatic members are considered. The problem of optimal design is to minimize the volume of the structure subject to the constraints that at given points of the structure the elastic displacements and the permanent plastic displacements caused by a one-parameter static load and by a...
Article
In case of dynamical analysis, the state variables depend on time. In the primal case, the equilibrium equations and the limit of the complementary elastic and kinetic energies are constraints and the sum of complementary energies is found in the objective function. The Stieltjes derivates are used to form the dual problem. It is bounded by the com...
Article
The physical nonlinearity of the structures is examined in the elastic state. The problem is solved by finite element method and nonlinear mathematical programming. For the second case both the primal and the dual problems are discussed. The different methods of the solutions are compared.
Article
Optimal design techniques have been extensively applied to structural design in case of one objective function. They have hardly been used with several objective functions. In this paper the multicriterion optimization of reinforced concrete frames is considered and the numerical method for determining the Pareto optimal set of the problem is prese...
Article
1. Abstract In the engineering practice it is very common that during the analysis and design process the designers should take into consideration time dependent loading and/or the state variables are time dependent, as well. The inelastic structural behaviour with a given load history can be solved by step-by-step methods what are connected to tim...
Article
Full-text available
New classes of exact, analytically derived structural topologies are outlined, their underlying theory summarised, illustrative examples given and their numerical, FE-based confirmation by the DCOC/SIMP method presented..
Article
Full-text available
The optimal design of elasto-plastic structures subjected to multiparameter (normal) loads and earthquake is presented. It is assumed that under normal loads the structure remains in elastic stage. In case of earthquake, different approximate methods are used in which the plastic reserve of the structure and viscous effects are also taken into acco...
Article
Full-text available
A new type of probability based topology design procedure is introduced. The standard deterministic mathematical programming problem formulation is based on a minimum volume design procedure which is subjected to a compliance and side constraints. The loads and the supports are given by the usual way and the applied distribution functions and the m...