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Contents

Introduction

There are different ways to evaluate the stability of a structure. It is important to know the differences between those methods and the limits of applicability but it is also important to recognize the equalities in pure cases.

Methods of stability design

In Eurocode 1993-1-1, and so in Consteel, there are 3 methods to verify the stability of a model:

The structural model is subjected to appropriate geometrical imperfections and after completing a second order analysis, only the cross section resistances need to be checked

       The method is based on two essential simplifications:

  1. Structural member isolation: The relevant member is isolated from the global structural model by applying special boundary conditions (supports, restraints or loads) at the connection points which are taken into account in the calculation of the buckling resistance
  2. Buckling mode separation: The buckling of the member is calculated separately for the pure modes: flexural buckling for pure compression and lateral-torsional buckling for pure bending. The two effects are connected by applying special interaction factors.
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After introducing the Eurocode standards several theses have been published on the now much-discussed phenomenon of lateral-torsional buckling of steel structural elements under pure bending. According to that, researchers are working on the development of such new design methods which can solve the problems of the design formulae given by the EN 1993-1-1. This paper gives a detailed review of the proposals for novel hand calculation procedures for the prediction of LT buckling resistance of beams. Nowadays, the application of structural design softwares in practical engineering becomes more common and widespread. Recognizing this growing interest, the main objective of our research work is the development of a novel, computer-aided design method. In this paper, the details of a general type stability design procedure for the determination of the LT buckling resistance of members under pure bending are introduced. Here, the theoretical basis of the proposed method is clarified, the calculation procedure is detailed and some results for the evaluation of the appropriateness of the method are also presented. Based on the evaluations it can be stated that the new, general type design method is properly accurate and has several advantages on the stability check of beams under bending

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Badari, B., Papp, F.: On Design Method of Lateral-torsional Buckling of Beams: State of he Art and a New Proposal for a General Type Design Method. Periodica Polytechnica Civil Engineering 2015

In the second article of this series, Dr József Szalai of ConSteel Solutions demonstrates practical examples where the “General Method” of EN 1993-1-1 shows advantages compared to the conventional approaches.

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Szalai J. Practical application of the “General Method” of EN 1993-1-1 – New Steel Construction 2011

Clause 6.3.4 of EN 1993-1-1 describes a “General Method” for lateral and lateral torsional buckling of structural components, ideally suited to software applications. Although the UK National Annex places some limitations on the use of this method, it is possible that the approach will become more widely used.

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Szalai J. The “General Method” of EN 1993-1-1 – New Steel Construction 2011

The new versions of the EN 1993-1-1 (EC3-1-1) and the EN 1993-1-5 (EC3-1-5) standards have introduced the general method designing beam-column structures; see [1] and [2]. The design method requires 3D geometric model and finite element analysis. In a series of papers we present this general design approach. The parts of the series are the following:

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Papp F, Szalai J. New approaches in Eurocode 3 – efficient global structural design. Part 1: 3D model based analysis using general beam-column FEM. Terästiedote (Finnish Steel Bulletin), 5, 2010.

The new versions of the EN 1993-1-1 (EC3-1-1) and the EN 1993-1-5 (EC3-1-5) standards have introduced the general method designing beam-column structures; see [1] and [2]. The design method requires 3D geometric model and finite element analysis. In a series of papers we present this general design approach. The parts of the series are the following:
– Part 0: An explanatory introduction

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Papp F, Szalai J. New approaches in Eurocode 3 – efficient global structural design. Part 0: An explanatory introduction. Terästiedote (Finnish Steel Bulletin), 5, Helsinki, 2010.

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Wald F, Papp F, Szalai J, Vídenský J. Obecná metoda pro vzpěr a klopení. SOFTWAROVÁ PODPORA NÁVRHU OCELOVÝCH A DŘEVĚNÝCH KONSTRUKCÍ (Software Solutions for Steel and Timber Structures), pp. 48-57., Prague, 2010.

The portal frames composed of tapered welded I-shaped structural members play important roles in the industrial buildings. The application of the relatively thin plates and the optimized fabrication makes these structures being competitive against the light truss structures at least in the range of 24–36 meters span. Competition has resulted in lesser selfweights using thin plated slender cross-sections, which are sensitive to local buckling. However, the development of structures concerning local buckling was delayed in Hungary by the conservative specifications of the MSz 15024 standard. The application of the new EN 1993 standard may cause radical development in the design of tapered structural elements with relatively thin plates. This paper introduces the methods as well as the advantages of the new design methodology.

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Papp F. Változó gerincmagasságú keretszerkezet tervezése az EN 1993 szabvány szerint a ConSteel programmal. MAGÉSZ ACÉLSZERKEZETEK II:(3) pp. 40-53. (2005)

The EN 1993 Part 1-1 (EC3-1-1) has introduced a new approach (called the “General Method”) to perform lateral-torsional buckling (LTB) assessment of beam-column structural components on the basis of elastic stability analysis. In the last years great research investigations went into the development of the method, see for instance [11,12] and also into the improvement of appropriate design software that is suitable to include the method and applicable for practical solutions [10]. The general objective of this paper is to review this issue from the point of view of the practice and contribute more effectively to understanding and resolving issues in the fields of practical application of the General Method. It is essentially significant to define the minimal analysis tools for the practice which are required for the accuracy of the method but on the other hand simple enough to make the modeling and calculation efficient. The paper briefly presents the theoretical background and the practical application of the elastic stability analysis of beam-columns that is necessary for the accurate evaluation of the General Method. The elastic stability analysis is verified by benchmark examples and also by shell finite element analysis. The application of the design method is demonstrated in the field of irregular structural members, especially web-tapered members and frames. The paper analyses the new theoretical results in the field of LTB of webtapered members that have led to prohibitive statements in some National Annex for EC3-1-1 concerning the segment method in the analysis of these members. It is shown that a comprehensive design method that is based on an appropriate segmented model and the General Method is efficient as well as reliable for conceptual design and with some restrictions also for detailed design.

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Szalai J, Papp F. Theory and application of the general method of Eurocode 3 Part 1-1. 6th European Conference on Steel and Composite Structures. Edited by Dunai L at al. 2011