The Effect Of Induced Imperfections On TheFormation Of The First Lobe Of SymmetricProgressive Buckling Of Thin- Walled SquareTubes

Abstract

An experimental investigation showing the effect of induced imperfections on the symmetric progressive buckling of thin-walled square mild steel tubes is presented. The imperfections include: a circular hole; indentations of various shapes; and combinations of a hole positioned centrally in an indentation. In all cases identical imperfections were induced symmetrically in opposite walls of the tube. The results indicate that the ultimate buckling load of the tube decreases with an increase in the severity of the imperfection. The distance between the plastic hinges that form the first lobe of buckling decreases with two opposing holes, but increases with large indentations. The change in the size of the first lobe leads to instabilities in the symmetric buckling mode which in turn leads to a decrease in the stroke of the tube. The results further indicate that combining a hole with an indentation has a cumulative effect on both the ultimate buckling load and the size of the first lobe. The stability of the symmetric progressive buckling of the tube is retained while decreasing the ultimate buckling load significantly for a range of indentation sizes and hole diameters.