Geometric and material nonlinear analysis of steel members with nonsymmetric sections

Steel members using nonsymmetric sections are often used for their structural efficiency in contemporary construction. Notwithstanding, the conventional concentrated plasticity (CP) analysis approach is commonly used in material nonlinear analysis and derived for regular hot-rolled steel sections with symmetrical shapes, leading to significant differences when analyzing members with nonsymmetric sections. This research develops the modified tangent modulus (MTM) method, proposed by Ziemian and McGuire in 2002, for the material nonlinear analysis of steel members with nonsymmetric sections, as a straightforward extension of the conventional CP analysis approach. Regarding the geometric nonlinear behaviors, an improved line-element formulation is formulated based on the nonsymmetric section assumption, explicitly modelling the noncoincidence of the shear center and centroid for considering the Wagner effects, which can capture complex buckling behaviors of the members with nonsymmetric sections. As part of the proposed method, a rigorous cross-section analysis method has been developed to generate the yield surfaces of arbitrary steel sections regardless of shapes. Such yield surfaces will be used to evaluate the full-yield condition, and the gradients to the yield surfaces will be calculated and used to control the plastic flow. The development of this methodology is presented in detail, as well as the derivation of the mathematical formulations. Six groups of verification examples are provided to validate the accuracy of the proposed method.