Stress Concentrations in Steel Structural Details: A Linear Strain-Based Approach for Cyclic Plasticity

Fatigue verification of steel structures is commonly carried out using stress-based criteria derived from elastic analyses. This approach is well established for high-cycle fatigue, characterized by predominantly elastic material behavior. However, it becomes less effective when cyclic loading induces localized plasticity at critical structural details, leading to fatigue damage governed by strain-driven mechanisms not explicitly addressed within conventional linear design frameworks. This work proposes a strain-based methodology to evaluate monotonic and cyclic plastic behaviour, as well as low-cycle fatigue damage, in steel structural details using only the results of linear elastic finite element analyses. The approach is based on Neuber's rule, combined with Ramberg-Osgood monotonic and cyclic material laws, the Smith-Watson-Topper parameter for mean-stress effects, and Miner's rule for cumulative damage. Notch effects are introduced through the fatigue stress concentration factor Kf, enabling a clear distinction between elastic stress amplification Kt and fatigue-relevant local response. The methodology is applied to two case studies. A perforated plate under monotonic loading is benchmarked against a materially nonlinear finite element solution, clarifying the domain of applicability of the method. A welded beam-to-column joint subjected to seismic loading demonstrates the complete cyclic workflow at structural scale, including rainflow counting, local elasto-plastic correction and cumulative damage evaluation. The results confirm that the proposed approach provides practical and computationally efficient estimates of local fatigue demand at steel structural details.