Theoretically, a member can only behave linearly while the maximum stress does not exceed the yield stress, and so the presence of residual stresses or stress concentrations will cause early non-linearity. However, the high ductility of steel causes a local redistribution after this premature yielding, and it can often be assumed without serious error that the member response remains linear until more general yielding occurs. The member behaviour then becomes non-linear and approaches the condition associated with full plasticity.