A procedure is developed to determine the safety factors of straight beams with rectangular cross-sections. To represent material behavior, a variety of stress-strain curves were used. The material of the beams was chosen to possess smooth changing stress-strain relations. The results were compared with those results of beams for which stress-strain relations had been idealized as linear elastic-perfectly plastic. The procedure in determining yield and fully plastic moments utilized a computational technique. Loads were increased incrementally up to rupture and the modified Newton-Raphson method was used to find the stresses. Experiments were performed to prove the validity of the analytic results. The reliability of a system using such structural elements can be predicted with the safety factors developed in this work. Copyright (C) 1996 Elsevier Science Ltd.