Tests of Circular Steel Tubes in Bending

A series of tests on 10-3/4in. (270-mm) tubes was conducted to determine the plastic rotation capacity of tubular beams. Six different D/t values ranging from 18-102 were used in the tests. Cantilever and fixed-ended beams, with moment gradients (shears) and restraints against ovalizing at the end, are compared with the behavior of the constant moment region of simple beams. Tubes with D/t greater than about 50 do not have sufficient plastic hinge rotation capacity to develop the classical ultimate strength. In the absence of a small moment gradient or stiffening, the plastic moment is not quite reached in tubes with D/t of 35. For inelastic buckling in the range of D/t of 18-80, critical strains appear to be proportional to (t/D)2, as opposed to the conventionallinear relationship. Information concerning the complex post-buckling behavior is also presented.