Plastic twisting and bending of an I-beam in which the warp is restricted

Summary An approximate lower bound solution is obtained for the fully-plastic twisting and bending of an I-beam in which warping of the cross-section is prevented at the ends of the beam. In the particular case when the applied bending moment is zero the solution enables the fully-plastic torque for pure torsion to be obtained from a torsion test with stiff end-plates. A lower bound solution is also obtained for the increase in twisting moment which is observed to occur when an I-beam is twisted in pure torsion beyond the point for full plasticity. The validity of the theories is confirmed by experiments.