THE LARGE-DEFLECTION PURE BENDING PROPERTIES OF A SQUARE THIN-WALLED TUBE

The moment rotation properties of square thin-walled tubes were measured up to and beyond bending collapse with a unique bending machine that was capable of applying a pure bending moment to large deflections without significant shear or tensile forces. This allows an accurate determination of a tube's maximum moment and plastic behaviour prior to collapse, the rotation at which collapse is initiated, as well as the resulting collapse curve. The results were compared with existing analytical predictions. In addition, the finite length of the local plastic collapse mechanism was determined by adjusting the deformable length of the test specimens. The concept of a finite mechanism length is important for the purposes of modelling the behaviour of structures such as bus frames that are commonly made from thin-walled tubes.