Nonlinear Analysis of Steel Frames Using Element with Trilinear Model

Considering the elastic-plastic stage of steel constitutive relationship, the assumption that element is elastic perfectly-plastic is no longer valid. The yield function that considers the effect of trilinear model is derived by using section assemblage concept. Element with two subsprings at each end is presented to consider the effect of section stiffness and yielding. Based on the proposed yield function and element, an efficient nonlinear analysis method for steel frame with trilinear model is proposed. The proposed element has the same nodal degrees of freedom as conventional beam-column element by condensing the non-nodal degrees of freedom. Other factors influence the capacity of steel frames, such as shear deformation, residual stress, geometric and material nonlinearity are explicated. The efficiency and accuracy of the proposed approach are demonstrated through the numerical example.