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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 93
PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping, J.M. Adam, F.J. Pallarés, R. Bru and M.L. Romero
Paper 228

Stability of Stiffened Cold-Formed Steel I-Sections using the Bubble Finite Strip Method

H.R. Naderian1, M. Azhari2 and H.R. Ronagh3

1Department of Civil Engineering, Yazd University, Iran
2Department of Civil Engineering, Isfahan University of Technology, Iran
3School of Civil Engineering, University of Queensland, Brisbane, Australia

Full Bibliographic Reference for this paper
H.R. Naderian, M. Azhari, H.R. Ronagh, "Stability of Stiffened Cold-Formed Steel I-Sections using the Bubble Finite Strip Method", in B.H.V. Topping, J.M. Adam, F.J. Pallarés, R. Bru, M.L. Romero, (Editors), "Proceedings of the Tenth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 228, 2010. doi:10.4203/ccp.93.228
Keywords: buckling, I-sections, bubble functions, complex finite strip method, cold-formed, stiffened.

Summary
The buckling modes of thin walled cold-formed steel members may be local, distortional or global [1]. This paper is concerned with stability of stiffened as well as unstiffened cold-formed steel I-sections under compression and bending loadings using the semi-analytical complex bubble finite strip method.

Bubble functions have been hitherto used to augment finite element formulations to obtain rapid convergence. Azhari and Bradford deployed bubble functions [2] to the ordinary complex finite strip method [3] and showed that very few strips are required in order to obtain an accurate solution.

The bubble finite strip method is programmed and used to investigate the elastic buckling of cold formed steel I-section columns and monosymmetric I-beams containing longitudinal flange stiffeners. The influence of longitudinal flange stiffeners on the stability of cold-formed I-sections is also surveyed. Furthermore, a comparison between stiffened and unstiffened cold-formed I-sections is made for different buckling modes. The accuracy of bubble finite strip method in predicting the buckling moments of monosymmetric cold-formed I- beams in comparison with generalized beam theory method [4] will be established.

Case studies are performed for different geometric properties of sections and stiffeners on the buckling behavior of cold-formed steel I-sections. It is shown that the inclusion of flange stiffeners is responsible for the existence of distortional buckling; however, this mode is not always critical. It is demonstrated that the variation of web thickness has some advantages as well as disadvantages on buckling strength of cold-formed I-sections. It can be seen for some of the sections with special geometric properties that the local buckling stress occurs at two points. Case studies on monosymmetric I-beams show that buckling curves concerning positive and negative moments are qualitatively different. It will be concluded that the possibility of local buckling increases by increasing the flange stiffener width in cold-formed monosymmetric I-beams. In other words, by decreasing the flange stiffener width the distortional buckling is more likely.

References
1
S. Ádany, B. Schafer, "Buckling Mode Classification of Members with Open Thin-Walled Cross-Sections", Fourth International Conference on Coupled Instabilities in Metal Structures Rome, Italy, 27-29 September, 2004.
2
M. Azhari, M.A. Bradford, "Local Buckling by Complex Finite Strip Method Using Bubble Functions", Journal of Engineering Mechanics, 120(1), 1994. doi:10.1061/(ASCE)0733-9399(1994)120:1(43)
3
R.J. Plank, W.H. Wittrick, "Buckling Under Combined Loading of Thin Flat Walled Structures by a Complex Finite Strip Method", International Journal for Numerical Methods in Engineering, 8, 323-339, 1974. doi:10.1002/nme.1620080211
4
P.B. Dinis, D. Camotim, N. Silvestre, "GBT Formulation to Analyze the Buckling Behaviour of Thin-Walled Members with Arbitrarily Branched Open Cross-Sections", Thin-Walled Structures, 44, 20-38, 2006. doi:10.1016/j.tws.2005.09.005

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