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Teil 1: Unterschiede bei der Stabilitätsausnutzung

Der Eurocode EN 1993-1-1 bietet grundsätzlich zwei Verfahren für die Stabilitätsnachweise von Stäben und stabartigen Strukturen an:

(1) basierend auf Abminderungsfaktoren (Knickkurven) und

(2) basierend auf (äquivalenten) geometrischen Imperfektionen.

Dieser Artikel zeigt, wie sich diese beiden Methoden in Bezug auf die endgültige Stabauslastung zueinander verhalten. Der Einfachheit halber betrachten wir nur rein druckbelastete Stäbe, die Biegeknicken unterliegen. Für Fall (1) wird Kapitel 6.3.1 verwendet, während für Fall (2) angenommen wird, dass die Imperfektionen die Form einer Knickfigur entsprechende Kapitel ist 5.3.2 (11)annehmen.

Es ist eine offensichtliche Erwartung, dass diese zwei Standardverfahren die gleiche Ausnutzung für das gleiche Problem ergeben sollten. Dies ist jedoch im Allgemeinen bei weitem nicht der Fall.

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Introduction

This verification example studies a simple fork supported beam member with welded section equivalent to IPE360 (flanges: 170-12,7; web: 347-8) subjected to biaxial bending due to concentrated end moments and compression due to axial force. Second order deformations of the middle cross-section of the member are calculated by hand and by the ConSteel software using both 7DOF beam and shell finite elements and Superbeam function. In addition to the verification, the difference between modelling with 6DOF and 7DOF elements is demonstrated.

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Gewöhnlich zeigt traditionelle baustatische Software die Verformungen von Balken mit ihren Querschnitten auf der verformten Schwerachse. ConSteel 15 dagegen benutzt eine fortschrittliche Methode für Deformationsdarstellungen, die feiner und realistischer ist. Natürlich sind die numerischen Ergebnisse identisch, aber mit der verfeinerten Visualisierung kann das 3D-Verhalten der Balkenstruktur besser erkannt werden.

Comparison of chosen methods for estimation of critical lateral torsional buckling bending moment of web-tapered I-beams. In this article, the elastic critical bending moments of the web-tapered I-beams calculated by the analytical and numerical solutions developed last years by researchers involved in the topic were compared with own calculations carried out with available common tools. The main goal was to verify the accuracy and convergence of the results provided by different modern methods and different finite bar elements 1D with 7 degrees od freedom at the node (7DOF).

Click the button bellow to download and read the full article. (PL)

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D. Czepiżak, A. Machowiak: Comparison of chosen methods for estimation of critical lateral torsional buckling bending moment of web-tapered I-beams. Inżynieria i Budownictwo Nr 5–6/2021

The calculation of the critical temperature is available in Consteel since the release of version 14. As an introduction of this feature, we prepared a video that gives some theoretical background on the topic, and demonstrates its usage in Consteel. It is shown how to prepare the model, how to execute the analysis and design, and how to create documentation about the critical temperature results.

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Consteel 14 is a powerful analysis and design software for structural engineers. Watch our video how to get started with Consteel.

Contents

Part 2 – Imperfection factors

The Eurocode EN 1993-1-1 offers basically two methods for the buckling verification of members:

(1) based on buckling reduction factors (buckling curves) and

(2) based on equivalent geometrical imperfections.

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This article aims to cover the theoretical background of the shear field stiffness determination methods implemented in Consteel. Modeling with the shear field stiffness based method will also be compared with shell modeling of trapezoidal deckings in Consteel.

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Modeling of tapered elements

Stability calculation of tapered members is always a difficult problem despite its popularity in steel hall construction.

Generally in analysis software for the stability analysis a segmented but uniform beam element method is used where a member with I or H cross section and with variable web depth is divided into n segments and the depth of each segment is taken equal to the real depth measured at the middle of the segment. The lengths of the segments were taken equal, except at both ends where additional shorter segments are added in order the better approximate the real depth of the elements to be modeled. Such model captures correctly the in-plane displacements, but cannot consider accurately the additional torsion coming from the axial stresses due to warping in the flanges which are not parallel with the reference line in case of tapered elements.

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Introduction

As you may already know, you can check the max, min and min-max envelope diagrams for (first and second order) analysis results in Consteel. But you can also create your own envelope figures…

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