INFLUENCE OF NONLINEARITY ON THE LOAD BEARING CAPACITY OF STEEL STRUCTURES

Abstract

The nonlinear behavior of steel structures has a significant effect on both their safety and the efficiency of material usage. In real structures, the influence of physical nonlinearity associated with the onset and development of plastic deformations, as well as geometric nonlinearity due to second-order effects, cannot be ignored, especially for slender and spatial systems. This study examines the combined influence of material and geometric nonlinearity on the behavior of steel structures by comparative numerical analysis. The novelty of the study lies in the combined use of GOST (government standard) and EN-based stress–strain curves within a 3D LIRA-FEM 2024 model for direct comparison of linear and nonlinear structural response. A 3D industrial steel frame composed of columns, roof trusses, and vertical and horizontal bracing was investigated using both linear and nonlinear FEM (finite element method) formulations. The frame response was evaluated under representative ULS (ultimate limit state) and SLS (serviceable limit state) load combinations formed in accordance with EN 1990, using actions defined in EN 1991. Geometric nonlinearity was accounted for through a large-displacement formulation of nonlinear finite elements, without introducing explicit code-based initial geometric imperfections, while material nonlinearity was represented by nonlinear stress–strain behavior. The comparison showed that the nonlinear analysis generally led to higher displacements and a redistribution of internal forces relative to the linear model, with corresponding changes in stress patterns. The results indicate that accounting for nonlinear effects provides a more realistic assessment of structural performance and can support more rational steel consumption while maintaining structural reliability.