Transition from initial global bending to progressive buckling of tubes loaded statically and dynamically

An experimental study is reported on the static and dynamic axial crushing of 128 thin-walled mild steel columns which buckled mostly in the plastic range. The columns have six different square cross sections (5.5 ≤ C/t ≤ 38) and five different circular cross sections (9.6 ≤ 2Rt ≤ 48), with a range of different lengths sufficient to encompass both progressive buckling and global bending (2.4 ≤ LC ≤ 51.2 and 2.2 ≤ L2R ≤ 35.9). For dynamic crushing, the columns are struck axially at one end by masses travelling with initial impact velocities of up to 12.14 m/s. It is observed that even relatively short columns, which enter the plastic range in a straight configuration, buckle (plastically) in the global inelastic buckling mode, while a transition to progressive plastic buckling is observed later in the collapse process. Some elementary theoretical considerations are presented on the initiation of the collapse process for tubes having square cross sections and on the transition from global bending to progressive buckling induced by the local plastic collapse for both circular and square tubes.