Inelastic behavior of steel members under nonproportional loading

Steel structures are often designed based on their ultimate strength. Therefore, understanding of the inelastic behavior of steel structural members is essential. This study is concerned with the development of a model for the inelastic behavior of steel members under cyclic and nonproportional loading. Based on the 1983 two-surface plasticity model developed by Tseng and Lee, an analytical model relating the force and strain (instead of the force and displacement) is formulated. The proposed model is verified through an experimental program that includes different combinations of non- proportionally applied forces such as pure bending, bending plus prescribed axial load, and nonproportionally applied axial load and bending moment.