Flexural behavior of corroded steel beams with and without web openings: experimental, analytical, and numerical investigation

Abstract

Corrosion is one of the most critical deterioration mechanisms affecting steel structures, since it reduces plate thickness, modifies geometric and mechanical properties, and may lead to instability, thereby compromising structural safety and load-carrying capacity. In steel beams, especially castellated beams, comprehensive studies that address the combined effects of corrosion on flexural response and local instability mechanisms remain limited, particularly regarding web-post buckling. In this context, this thesis investigates the flexural behavior of corroded steel beams with and without web openings through experimental, analytical, and numerical approaches, considering ASTM A572 Grade 50 and Grade 60 steels. The experimental program comprised tensile tests on coupons extracted from the steel profiles, three-point bending tests on solid-web and castellated beams under both corroded and uncorroded conditions, and Digital Image Correlation analyses to characterize surface imperfections, lateral displacements, and strain fields. The results showed that, in corroded solid-web beams, corrosion promoted local buckling before full cross-sectional yielding, thus changing the governing resistance mechanism. In castellated beams, corrosion significantly increased susceptibility to web-post buckling, leading to substantial reductions in load-carrying capacity of 39.05% for Grade 50 steel and 35.85% for Grade 60 steel, while the steel grade itself had no significant influence on the overall web-post buckling mode. DIC analyses further revealed localized strain concentrations around corrosion pits and earlier yielding in the tensile tie region of the web-post. Pit-depth measurements were statistically described by a log-normal distribution, with logarithmic mean and standard deviation values of 0.7951 mm and 0.3865 mm for Grade 50 steel, and 0.8918 mm and 0.4636 mm for Grade 60 steel. Based on experimental evidence, a non-empirical analytical formulation was proposed to estimate the critical load associated with web-post buckling in both corroded and uncorroded castellated beams. Compared with Steel Design Guide 31 and EN 1993-1-13:2024, the proposed model provided closer agreement with the experimental results, with lower average deviations than the code-based approaches. In parallel, a finite element model was developed in ABAQUS using a stochastic representation of corrosion based on a spatially correlated Gaussian random field. The calibration process indicated that a 15 mm mesh and a spatial correlation factor of ρf = 0.75 yielded the best agreement with the experimental load-displacement curves and successfully reproduced the corrosion-induced shift in structural behavior. Overall, the thesis advances the understanding of corrosion effects on the flexural and instability behavior of steel beams and provides analytical and numerical tools for the assessment of corroded castellated members.