Sándor Ádány

Budapest University of Technology and Economics · Department of Structural Mechanics

In this research the effect of prebuckling in-plane deflections on the critical moment to lateral-torsional buckling of beams is investigated. Though this topic is already discussed in the literature, the relevant papers show that there are some discrepancies in the proposals and results from the various authors. In this paper numerical studies are...

The objective of this paper is to document and validate the extension of an open source finite strip method stability software (CUFSM) to include vibration analysis, and to demonstrate the application of the resulting solution to assess the stability and vibration of a prototype all-steel modular floor assembly. Currently, the open source finite st...

Wind turbine towers are highly slender and made of thin cylindrical shells with large diameter‐to‐thickness ratios, which means stability is an essential concern. The high diameter‐to‐thickness ratios of these cylinders make them highly imperfection sensitive, meaning their failure loads and failure modes are highly dependent on initial geometries....

In this research the effect of prebuckling in‐plane deflections on the critical moment to lateral‐torsional buckling of beams is investigated. Though this topic is already discussed in the literature, the relevant papers show that there are some discrepancies in the proposals and results from the various authors. In this paper a numerical parametri...

This paper provides an efficient and robust numerical solution for the linear buckling analysis of tubular members, such as the supporting tower structures of wind turbines. The method uses Fourier‐series approximations for the displacement functions. Longitudinal discretization can optionally be applied, i.e., the member can be divided into segmen...

Longitudinal stiffeners are widely used in plated structures to prevent buckling of the slender plate elements and, therefore, to increase the load bearing capacity of these structures. There has been extensive research in the past regarding the shapes, sizes, and placement of these longitudinal stiffeners, however, there has been little research t...

In this paper, the elastic lateral–torsional behavior of simple beams is discussed by presenting a novel analytical solution and performing numerical studies. The motivation of the presented research is the observation that classic analytical prediction and finite element prediction are, typically, significantly different when the second-order nonl...

Keywords: Modal decomposition of thin-walled members Constrained finite element method Displacement mapping Arbitrary shell finite elements Members with holes A B S T R A C T Understanding and analyzing the complex behavior of a structural member is often achieved by decomposing it into simpler phenomena and interpreting it as a superposition of...

In this paper elastic lateral-torsional behavior of simple beams is discussed. The motivation of the presented research is the observation that classic analytical prediction and finite element prediction are, typically, considerably different, when the second-order nonlinear behavior of beams with initial imperfections is analyzed. In order to unde...

In this paper a new way to define transverse extension modes is introduced in the context of modal analysis of thin-walled members. The new transverse extension modes are inspired by the strain distributions of global and distortional modes. The new modes are employed here in the constrained finite strip method. The new modes require some change in...

Longitudinally stiffened plates appear in many structural engineering applications. One of the typical failure modes is induced by the buckling of the stiffeners, therefore enhancing our understanding of buckling behavior is of crucial importance. Recently, buckling resistance of longitudinally stiffened plates with trapezoid stiffeners has been in...

A widely used approach to understand and analyze the complex behavior of a structural member is to decompose the complex phenomenon into simpler ones, and then to interpret the complex phenomenon as the superposition of the simpler ones. Accordingly, the deformations of thin‐walled members are frequently decomposed into global, distortional, local‐...

Experience has shown that the durability of “high-modulus” asphalts made with modified bitumen is unsatisfactory. The misdirected “development” forced in recent decades necessitates a more accurate understanding of the mechanical behavior of rolled asphalts, i.e., constitutive formulation of a numerical asphalt model. The authors elaborate a numeri...

In this paper a novel analytical solution is presented for the geometrically nonlinear analysis of beams subjected to lateral torsional buckling, by assuming an initial geometric imperfection in the form of the buckled shape from a linear buckling analysis. The novelty of the solution is that it takes into consideration of the changing geometry as...

Buckling resistance of longitudinally stiffened plates subjected to compression is a crucial issue in the design of many steel bridges. The design methodology of the current Eurocode describes the behavior as a combination of column-like and plate-like behavior. Previous studies well explored the plate-like behavior of compressed stiffened plates w...

In this paper, a new version of the constrained finite element method is reported. The constrained finite method is essentially a shell finite element method, developed for the modal analysis of thin-walled members, where mechanical constraints can be applied to enforce the analyzed member to deform according to specific (e.g., global, distortional...

Masonry arch bridges form an integral part of our rail infrastructure network and their safety is important for the functioning of our society. Although, there have been several studies to understand the in-service condition of masonry arch bridges, these are mainly focusing on static analyses. However, it is well known that moving vehicles exert a...

In this paper the pure torsional buckling of thin-walled column members is investigated, with a special focus on the effect of transverse plate elements, such as end-plates or transverse stiffeners. The linear buckling problem is aimed to solve analytically, therefore the necessary (differential) equations are first established. For some simple pro...

In the presented work the mechanical behavior of a masonry arch bridge of a single-track railway is analyzed numerically. The 3D discrete element model contains the arch barrel, the backfill and the spandrel walls as well. Every voussoir is represented by a discrete element, while the backfill is modelled as an elasto-plastic continuum. Between the...

Buckling resistance of longitudinally stiffened orthotropic plates is highly important in the design of steel bridges. The current calculation method of Part 1.5 of Eurocode 3 is based on the concept that the behaviour can be superposed from plate-like and column-like behaviours. Recent results indicate uncertainties in the application of the curre...

In this paper the elastic buckling of longitudinally stiffened plates are discussed in the light of modal deformations. Though in the analysis and design of cold-formed steel members it is a widely used approach to decompose the deformations into global, distortional, local and other deformation modes, this approach has not been used for stiffened...

In this paper elastic major-axis flexural buckling of thin-walled lipped channel column members with slotted webs is discussed. Though slotted webs are applied in order to enhance the thermal properties (this is why these members are also known as thermal studs), the slots have non-negligible effect on the mechanical behaviour. The primary aim of t...

In this paper modal decomposition of thin-walled structural members with rounded corners is discussed. Modal decomposition is a process which separates the characteristic behaviour types. If modal decomposition is applied in buckling analysis, pure uncoupled buckling modes can readily be analysed, such as pure global buckling, pure distortional buc...

In this paper the buckling of lipped channel cold‐formed steel members with slotted web is discussed. These members typically have complicated buckling behaviour, since it is a combination of various types of buckling, such as lateral‐torsional buckling, distortional buckling, plate buckling, web crippling, or shear buckling. Though it is practical...

This paper investigates the mechanical behaviour of skew masonry arch bridges taking into account the arch ring-backfill interaction. A numerical model has been developed using the three-dimensional computational software 3DEC, based on the Discrete Element Method of analysis. Each brick of the masonry skew arch was represented as a distinct block....

Thin-walled structural members have complex behavior. It is usual to interpret the complex behavior as the superposition of simpler behavior components, like global, distortional, local, in-plane shear and transverse extension. When the standard shell finite element method is employed for the analysis, the behavior components are not separated, and...

In this paper modal decomposition of the deformations of thin-walled structural members are discussed. Modal decomposition is a process which separates the characteristic behavior modes. If applied in buckling analysis, modal decomposition makes it possible to analyze pure global or pure distortional buckling or pure local-plate buckling. Ability t...

This paper investigates the mechanical behaviour of skew arch bridges taking into account the arch ring-backfill interaction. Simulations were performed with the three dimensional computa-tional software 3DEC, based on the Discrete Element Method of analysis. Within 3DEC, each brick of the masonry skew arch was represented as a distinct block. Mort...

In this paper the constrained finite element method is applied for the buckling analysis of thin-walled members with holes. The method is basically a shell finite element method, but constraints are applied which enforce the member to deform in accordance with specific mechanical criteria, e.g., to force the member to buckle in flexural, or flexura...

This paper discusses a potential simple new design approach for cold-formed steel Z-purlins. The new design approach tries to simplify the traditional design procedure based on effective widths and thicknesses, which is necessarily complicated due to the complex behaviour of the purlin. The complexity of the behaviour is due to the high slenderness...

In this paper the buckling behaviour of thin-walled members with cross-sections with curved parts is investigated. Due to the curved parts, shell-like buckling is a potential mode of failure. The objective of the research is to understand whether shell-like buckling behaviour might be governing in practical cold-formed steel members. For this aim,...

In this paper local elastic and geometric stiffness matrices of ashell finite element are presented and discussed. The shell finiteelement is a rectangular plane element, specifically designedfor the so-called constrained finite element method. One of themost notable features of the proposed shell finite element isthat two perpendicular (in-plane)...

In this paper a novel method for the analysis of thin-walled members is presented: the constrained finite element method. The method is basically a shell finite element analysis, but carefully defined constraints are applied which enforce the thin-walled member to deform in accordance with specific mechanical criteria, e.g., to force local, global...

In this paper a novel method is employed for the buckling analysis of thin-walled members. The method is basically a shell finite element method, but constraints are applied which enforce the thin-walled member to deform in accordance with specific mechanical criteria, e.g., to force the member to buckle in flexural, or lateral-torsional or distort...

In this paper a novel shell finite element is introduced, specifically proposed for constrained shell finite element analysis. The proposed element is derived from the finite strips used in the semi-analytical finite strip method. The new finite element shares the most fundamental feature of the finite strips, namely: transverse and longitudinal di...

In this paper the generalization of the constrained finite strip method (cFSM) is provided. cFSM is an extension of the semi-analytical finite strip method (FSM), where carefully defined constraints are applied to enforce the thin-walled member to deform in accordance with desired deformations, e.g., to buckle in flexural, lateral-torsional, distor...

In this paper, flexural buckling of pin-ended thin-walled columns is discussed. The classical formulae for the critical force are based on a beam model. The simplest formulae use the classical Euler–Bernoulli beam theory, but solutions based on the shear-deformable beam theory are also known. In the presented research alternative formulae are deriv...

In this paper the elastic and geometric stiffness matrices of the semi-analytical finite strip method (FSM) are discussed. The stiffness matrices are derived in various options. New derivations are presented for different longitudinal base functions, which corresponds to column/beam member with general boundary conditions. Numerical studies are per...

In this paper flexural buckling of thin-walled members with holes are discussed. Members with few but large openings, as well as with slotted webs are studied. Large number of finite element analyses has been performed, by using a carefully constrained shell finite element model in order to exclude the distortion of the cross-section, which makes i...

In this paper the generalization of the constrained finite strip method (cFSM) is discussed. cFSM is a special version of the semi-analytical finite strip method (FSM), where carefully defined constraints are applied which enforce the thin-walled member to deform in accordance with specific mechanics, e.g., to allow buckling only in flexural, later...

In this paper a novel method is presented for the modal decomposition of thin- walled members. The proposed method follows the logic of the constrained finite strip method (cFSM), however, polynomial longitudinal shape functions are applied together with a longitudinal discretization. Thus, strips are transformed into multiple shell finite elements...

In this paper in-plane (membrane) shear deformations in thin-walled members are discussed. Unlike many earlier works on the effect of shear deformations, the actual work is based on shell model rather than beam model. Thus, the presented work has no intention to develop a new shear-deformable beam theory, by adding some assumed shear deformations t...

The stability of thin-walled members is decidedly complex. The recently developed constrained Finite Strip Method (cFSM) provides a means to simplify thin-walled member stability solutions through its ability to identify and decompose mechanically meaningful stability behavior, notably the formal separation of local, distortional, and global deform...

The objective of this paper is to provide a method for applying modal identification (i.e. the separation of general deformations into fundamental modal deformation classes: local, distortional, global, shear, and transverse extension) to the collapse analysis of thin-walled members modeled using material and geometric nonlinear shell finite elemen...

In this paper, the behavior of deep trapezoidal sheeting with perforated webs is studied. The analyzed panel has longitudinal stiffeners both in the webs and flanges, which improves the load-bearing capacity but makes the behavior more complicated. The considered panel is produced with and without web perforations. When web perforation is applied,...

The objective of this paper is to introduce and provide the latest developments in the constrained finite strip method (cFSM) and its application to cold-formed steel (CFS) member stability. The modal identification and decomposition features of cFSM provide a quantitative tool for assessing coupled instabilities. Extension of cFSM to general end b...

This paper illustrates new capabilities for modal identification of shell Finite Element Method (FEM) models of thin-walled cold-formed steel members. The separation of general deformations into fundamental buckling deformation classes: local, distortional, global, shear, and transverse extension, originated with the constrained Finite Strip Method...

In this paper global buckling (i.e., flexural, pure torsional, or flexural–torsional buckling) of thin-walled columns is discussed. The considered problem is the most basic one: the column is simply supported and subjected to a uniform concentric compressive force. The column's cross-section is an arbitrary open thin-walled cross-section. For the c...

In this paper numerical studies on global buckling of thin-walled members are presented. Various methods are used including classical analytical solutions, the semi-analytical finite strip method, the generalized beam theory, shell finite element method and the recently derived shell-model-based analytical formulae. Critical forces are calculated f...

This paper discusses the effect of rounded corners in the capacity prediction of cold-formed steel members. Three important aspects are identified and investigated by performing parametric numerical studies on a large number of beams and columns of various cross-sections. Calculations have been performed by using sharp and rounded corners, and by u...

This paper discusses mode identification for buckling modes calculated by shell finite element analyses. An automatic mode identification method has been previously proposed by the authors that uses a special system of modal base functions, referred to as cFSM base functions. Earlier studies proved the applicability of the approach, but also highli...

The objective of this paper is to explain and establish the sensitivity of the modal decomposition and modal identification capabilities of the constrained Finite Strip Method to choice of basis, orthogonalization, and normalization. The constrained Finite Strip Method provides a mechanical means to separate the deformations of a thin-walled member...

The objective of this paper is to provide a method for applying modal identification, (i.e. the separation of general deformations into fundamental buckling deformations classes: local, distortional, global, shear, and transverse extension) to collapse analysis of thin-walled members modeled using material and geometric nonlinear shell finite eleme...

The objective of this paper is to provide a method for applying modal identification, (i.e. the separation of general deformations into fundamental buckling deformations classes: local, distortional, global, shear, and transverse extension) to collapse analysis of thin-walled members modeled using material and geometric nonlinear shell finite eleme...

The objective of this paper is to demonstrate an approximate method whereby eigen buckling modes from a shell finite element method (FEM) analysis of a thin-walled member can be quantified in terms of the fundamental buckling classes, namely, global, distortional, local, or other. The buckling classes are defined using the mechanical definitions em...

The objective of this paper is to provide (i) the fundamental derivation details and (ii) a comparison between Generalised Beam Theory (GBT) and the constrained Finite Strip Method (cFSM), two alternative modal approaches to analyse the elastic buckling behaviour of unbranched thin-walled members. Thin-walled members may generally buckle in three f...

This paper presents a new design approach for the stability design of thin-walled members. The proposed approach is based on the buckling modes and critical forces/moments determined by a linear buckling analysis performed on a regular shell finite element model. A fully automatic buckling mode identification technique is applied, by using the moda...

This paper derives a new method for fully decomposing the elastic stability solution, of a thin-walled single-branched open cross-section member, into mechanically consistent buckling classes associated with global, local, distortional, and shear and transverse extension buckling modes. The method requires a set of formal mechanical definitions for...

This paper provides the first detailed presentation of the derivation for a newly proposed method which can be used for the decomposition of the stability buckling modes of a single-branched, open cross-section, thin-walled member into pure buckling modes. Thin-walled members are generally thought to have three pure buckling modes (or types): globa...

The objective of this paper is to provide implementation details of, and practical examples for, modal decomposition of the cross-section stability modes of thin-walled members by constraining a traditional finite strip method (FSM) solution. The theoretical development of the proposed method is provided in a companion to this paper [Ádány S, Schaf...

This paper demonstrates how to decompose general stability solutions into useful subclasses of buckling modes through formal definition of the mechanical assumptions that underlie a class of buckling modes. For example, a thin-walled lipped channel column as typically used in cold-formed steel can have its buckling mode response decomposed into loc...

The load-carrying capacity of thin-walled members is often governed by buckling phenomena. Usually, three main families of buckling phenomena/modes are considered: (i) global buckling, in which the member axis deforms (e.g., flexural or lateral-torsional buckling), (ii) local-plate buckling, involving only plate (wall) bending, and (iii) distortion...

This paper discusses some problems of the definition and calculation of elastic buckling of thinwalled members. Possible approaches for the definitions of local, distortional and global buckling are briefly summarized and evaluated through numerical examples, which also illustrate the existing uncertainties.

The paper presents a basic comparison between two approaches to solve thin-walled member buckling problems: Generalized Beam Theory (GBT) and the newly developed constrained Finite Strip Method (cFSM). The fundamentals of the two methods are briefly summarized, compared and applied to analyze the buckling behavior of a typical unbranched open-secti...

This paper presents the first results of an attempt to identify buckling modes calculated by a regular shell finite element analysis via the modal base functions produced by the constrained finite strip method, a method recently proposed by the Authors. The paper gives the mechanical criteria which are used for mode definition, as well as briefly s...

The paper discusses the flexural buckling of columns in the light of the finite strip and shell finite element methods. The assumed displacement field is thus more general than in classical buckling solutions that are based on beam model, and tries to simulate the assumptions on which finite strip and shell finite element method stand. The basic st...

Cross-section instability greatly complicates the behavior of thinwalled members. Current computational stability techniques do little to add clarity. The terms "global," "distortional," and "local buckling" permeate the literature, but there are no satisfactory definitions for the three characteristic modes. Despite this, design standards require...

This paper deals with the finite element modelling and analysis of end-plate joints in steel frames, under monotonic and cyclic loading conditions. In the first part of the paper the main characteristics of possible computational models are summarised and discussed, including remarks on finitisation possibilities, the applicable material models, no...

This paper proposes a new approach for buckling mode definitions of open cross-section thin-walled members, which, unlike the existing phenomenological definitions, are based on simple mechanical assumptions which can easily be applied in the context of any numerical method. The application of the proposed definitions to the Finite Strip Method is...

In this paper a method is discussed with the application of which the foundation depth can be taken into consideration in the seismic analysis. The main steps of the method are presented, the theoretical background is briefly summarised, then it is applied for practical examples. A parametric study is presented in which the effect of the foundation...

In this paper an experimental study is performed on end-plate type joints. The test arrangement represents a column-base joint of a steel frame. Altogether six specimens were tested, each of them subjected to cyclic loading. The specimens were carefully designed by performing detailed preliminary calculations so that they would present typical beha...

In this paper an experimental study is performed on end-plate type joints. The test arrangement represents a column-base joint of a steel frame. Altogether six specimens were tested, each of them subjected to cyclic loading. The specimens were carefully designed by performing detailed preliminary calculations so that they would present typical beha...

End-plate-type joints are widely used in steel frame structures, connecting either two steel elements (like beam-to-column, beam-to-beam or column-to-column joints) or a steel and a concrete/reinforced concrete element (like column-base joints or joints of a steel beam and a reinforced concrete column). Although these joints have numerous practical...

The importance of the joint cyclic behaviour is well-known in the seismic design of dissipative steel framed structures. The local ductility of joints has significant effect on the global ductility of the structure. The local ductility of the joints can be characterised numerically by the cyclic parameters. These are the obtained from the cyclic mo...

A parametric study on the cyclic behavior of steel bolted T-stub assemblies is presented. The numerical simulation is performed by a sophisticated finite element model. The actual values of the parameters are chosen so as to cover all the practical cases, including extremely strong and weak bolts. The results of the parametric study show the applic...

In this paper a model is introduced for the analysis of end-plate type steel-to-concrete connections under monotonic and cyclic loading. The developed model predicts the global response of the connection from the local behaviour of the 'tension' and 'compression' zones. The load-deformation relationships of the zones are analysed independently by t...

This chapter introduces a prediction model for the moment-rotation behavior of endplate type steel-to-concrete connections under combined axial force and bending moment. The developed model predicts the global response of the connection from the local behavior of the “tension” and “compression” zones. Steel-to-concrete mixed connections are connect...

The objective of this paper is to provide technical background and illustrative examples for stability analysis of cold-formed steel members using the conventional and constrained finite strip methods as implemented in the open source program CUFSM. Numerical stability analysis combined with an accurate identification of the buckling modes is an en...

Javaslatot tettünk vékonyfalú szelvények stabilitásvesztési módjainak új, mechanikai alapon történő definiálásra. Kidolgoztuk a cFSM (constrained Finite Strip Method) eljárást. A cFSM-mel tetszőleges nyitott keresztmetszetű két-csuklós prizmatikus rúd rugalmas stabilitásvizsgálata elvégezhető: tetszőleges tiszta vagy interakciós módhoz tartozó krit...