Bending hinge characteristic of thin-walled square tubes

Previous studies have shown that a global bending collapse hinge of thin-walled square metal tubes composed with a series of stationary hinge lines, rolling hinge lines and toroidal surfaces. In particular they have shown that the structures respond to quasi-static testing by means of an initial peak moment followed by a failing moment as deformation proceeds. This paper further studies, using finite element analysis, the bending collapse mechanism of thin-walled square metal tubes with a global hinge. Various finite element models are created with ABAQUS. Detailed numerical calculations are made in terms of the resultant moment-rotation curves, the overall collapse process, development of plastic hinge lines, profiles of the cross-section and distributions of stress and strain along the cross-section. Dimensional analysis theory reveals that the bending moment, M, depends on the ratio of width to thickness of the tube (b/l), the flow stress of the material (sigma(0)) and the corresponding rotation angle (theta). An empirical design formula for the bending moment is presented and compared with available test results. Finally, the strain-rate effect of the material is investigated for dynamic bending collapse of tubes.