A torsional fiber element and a multiaxial softening model to simulate cyclic interactive buckling in wide-flanged steel members

A three-dimensional frame-element based approach is presented to simulate cyclic inelastic interactions of local and lateral torsional buckling – collectively termed interactive buckling. The approach integrates a multiaxial fiber-based beam-column element termed the torsional fiber element, capable of representing deformation modes characteristic of inelastic warping and St Venant torsion with a multiaxial constitutive model that represents the effective constitutive response associated with cyclic inelastic local buckling. The resulting integrated approach, implemented in the platform OpenSees is applied to 26 beam-column specimens encompassing a range of configurations including section geometry and boundary conditions and loading protocols. The results of the approach are evaluated against counterpart results from physical experiments as well as continuum finite element simulations. It is determined that the presented approach can simulate important aspects of interactive buckling both qualitatively and quantitatively, including deformation modes, as well as cyclic strength and stiffness degradation, while requiring only a fraction of the computational time of the continuum-finite element simulations. Guidelines for calibration and use of the approach are presented. Limitations of the approach are summarized, along with directions for future improvements.