Keywords: torsion with warping, open and closed cross-sections, secondary torsion moment deformation effect, experimental verification, numerical analysis.

The last results of theoretical research [1,2,3] have shown that the effect of warping must be considered also in the case of torsion of constant closed cross-sections. Additionally, the inaccuracy of the thin-tube theory in calculating the secondary torsion constant has been observed [4,5]. Hence, it is straightforward to carry out measurements of the most significant features of non-uniform torsion: the total torsion angle, the warping displacement and the normal stress caused by a bimoment. It is worth pointing out that there do not seem to be any relevant experimental results accessible. This has been a strong motivation for us to deal with the design of a new measurement device which would be able to measure deformations and normal stress caused by non-uniform torsion.

This paper represents a valuable contribution in the analysis of thin-walled beams subject to non-uniform torsions. The authors' novel approach includes semi-analytical and numerical analyses and the measurement of some key warping-torsion features. For the measurement a specially designed measurement device has been built [6]. The majority of the results obtained are in a good agreement with theoretical predictions. However, the numerical analysis of the closed cross-sections, as carried out using commercial software, differs significantly from measurement. As expected, the importance of the inclusion of warping in the analysis of the closed cross-sections has been confirmed experimentally. This is in contradiction to the widely used Eurocodes [7,8].

1

H. Rubin, "Zur Wölbkrafttorsion geschlossener Querschnitte und ihrer Irrtümer - Grundlagen", 29th Stahlbauseminar, Band 140, 2007.

2

H. Rubin, M. Aminbaghai, H. Weier, "IQ-100. The civil engineering structures program", TU Vienna, Bautabellen für Ingenieure, Werner Verlag, 17. Auflage, 2006.

3

J. Murin, V. Kutis, "An Effective Finite Element for Torsion of Constant Cross-Sections Including Warping with Secondary Torsion Moment Deformation Effect", Engineering Structures, 30(10), 2716-2723, 2008. doi:10.1016/j.engstruct.2008.03.004

4

V.G. Mokos, E.J. Sapountzakis, "Secondary torsional moment deformation effect by BEM", International Journal of Mechanical Science, IJMS-10323R1, 2011. (Accepted for publication) doi:10.1016/j.ijmecsci.2011.08.001

5

V.G. Mokos, E.J. Sapountzakis, "A Three-Dimensional Beam including Torsional Warping and Shear Deformation Effects arising from Shear Forces and Secondary Torsional Moments", in B.H.V. Topping, Y. Tsompanakis, (Editors), "Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 137, 2011. doi:10.4203/ccp.96.137

6

J. Murin, T. Sedlar, A. Kalas, V. Kralovic, "A device for measurement of non-uniform torsion of the thin-walled cross-sections", Patent 6017 Slovak Republic, 2012. (In Slovak)

7

EC-3 Eurocode 3, "Design of steel structures"

8

EC-9 Eurocode 9, "Design of aluminium structures"

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