Eelastic and geometrically nonlinear buckling response of hea steel columns with varying end restraints

Abstract

The buckling behavior of HEA steel columns, which are widely used as columns and frame members in steel structural systems, is directly influenced by parameters such as member length, material properties, and end support conditions. In conventional design, column ends are generally idealized as either pinned or fixed. However, in practice, column end behavior may vary between these two ideal conditions. In this study, the effects of end rotational stiffness on the elastic buckling and geometrically nonlinear buckling behavior of HEA steel columns were investigated numerically. A 5000 mm long HEA200 steel column was modeled in ABAQUS using S4R shell elements. The weak-axis rotational restraint was represented using connector elements. The dimensionless parameter ρ, defined as the ratio of the connector rotational spring stiffness to the column's characteristic flexural stiffness, was investigated over a wide range, from pinned to fixed-end behavior. Eigenvalue buckling loads obtained from the finite element analyses were compared with theoretical Euler solutions for commonly used ideal end conditions. For each model, the first buckling mode was defined as the initial geometric imperfection with an amplitude of L⁄1000, and Static Riks analyses were performed. The nonlinear buckling behavior of the columns was evaluated using the load proportionality factor (LPF=P⁄(Pcr)) and the weak-axis lateral displacement (U1) at column mid-height. The results showed that increasing end rotational stiffness increased the elastic critical buckling load and reduced the effective length factor. As the normalized load approached the critical region, lateral displacements increased, and the influence of end rotational stiffness became more pronounced. At high ρ values, both the elastic and geometrically nonlinear responses approached the fixed-end condition asymptotically.