Sensitivity Analysis of Initial Imperfection in Low Torsional Stiffness Cruciform Steel Columns

Cruciform steel columns are widely employed in diverse structural applications due to their advantages, which include flexible layout configurations and reduced self-weight. However, these columns possess inherently low torsional stiffness, making them particularly vulnerable to the effects of initial imperfections, especially initial torsion, which can be especially detrimental. Current design standards, such as GB 50017, Eurocode 3, and AISC 360, do not take initial torsional imperfections into consideration. This omission can result in potential inaccuracies in structural evaluations and may compromise overall safety. In this study, nonlinear finite element modeling (FEM) was performed using ANSYS software with Solid45 elements. The analysis accounted for both geometric imperfections and residual stresses, and its accuracy was validated through eigenvalue and nonlinear buckling analyses, with error margins remaining below 5%. The main findings indicate that the width-to-thickness ratio (b/t ≈ 18.5) is a critical factor influencing the transition between elastic and plastic behavior, as well as contributing to a reduction in load-bearing capacity. Initial torsion within the range of 0–5° was found to have the most significant negative impact on the bearing capacity of the columns. Residual stresses were shown to further aggravate this effect, with notable coupling interactions. Additionally, when the slenderness ratio (\(\lambda\)) relative to the b/t ratio (k < 5.18) is low, the detrimental influence of initial torsion is considerably amplified. This research helps to fill existing theoretical gaps, reinforces the foundational basis for stability analysis, and offers valuable insights that can inform future revisions of structural design codes.