The strength of thin-walled tubes formed from flat elements

Abstract Compression tests were undertaken to examine the influence on maximum strength of forming tubes from thin steel sheet with increasing numbers of flat elements. The tubes in a given series were manufactured from sheets having equal thickness, length and total width, although the number of sides ranged from 4 to 40. The cross-section perimeter of all tubes was equal to that of a circular tube, 8 in. diameter, so that for a given sheet thickness all tubes had the same cross-sectional area. The relationship between maximum strength and number of sides was approximately linear for tubes having up to 18 sides, and the mode of collapse was elastic buckling of the elements followed by plastic collapse at the junction between adjacent elements. Tubes with 22 sides and above collapsed in a mode similar to that for a true circular tube (with the junction between adjacent elements snapping inwards) and the maximum strengths were in the range for circular tubes of equal area and wall thickness. An approximate analysis was shown to give reasonable agreement with test results.