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This and the next 3 images are from:
J. Loughlan (1) and M. Nabavian (2)
(1) Dept. of Aircraft Design, College of Aeronautics, Cranfield Institute of Technology, England
(2) McDermott Engineering London, Membley, Middlesex, England
“The behaviour of thin-walled columns after local buckling”, 8th International Specialty Conference on cold-Formed Steel Structures, St. Louis, Missouri, USA, 11-12 November, 1986, Paper 2
ABSTRACT: In this paper an outline is given of a theoretical approach which is able to predict the equilibrium behaviour of thin-walled, pin-ended, I-section columns after local buckling. The extreme changes in cross- sectional shape that occur during overall bending of the locally buckled column are accounted for quite easily in the analysis by the inclusion of several local deflection shape functions. The changes in cross-sectional shape that occur during the pure compressional phase of behaviour, prior to overall bifurcation, are also accounted for in the analysis. The Rayleigh-Ritz method is used to obtain local buckling loads and a semi-energy method is employed to describe post-buckling interaction behaviour. It is shown that, although all columns exhibit stable equilibrium behaviour after local buckling, the quality of the equilibrium at failure due to overall bifurcation, can be unstable to varying degrees depending on geometry. It is also shown that the theoretical predictions of equilibrium behaviour and ultimate loads are significantly influenced by the number of local deflection shape functions incorporated in the post-buckling analysis. If insufficient functions are employed in the solution, a considerable overestimate of stiffness and hence ultimate load can result. The analysis is able to accommodate eccentricity of applied loading and column axis imperfection in which case, overall bending would occur from the onset of loading. A study is made of the effect of column axis imperfection on the ultimate carrying capability of thin-walled I-section columns and it is shown that, I-sections are appreciably sensitive to this mode of imperfection over a wide design range. Results are presented in the paper in the form of load-deflection equilibrium curves and ultimate load-slenderness plots. A comparison of the theory with independent experimental work is also included and agreement is seen to be good.
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