Corrosion-Induced Ductile-to-Brittle Transition in RC Frames: A Parametric 3D FEM Study and Failure Mechanism Mapping

The corrosion of steel reinforcement poses a significant threat to the safety and longevity of reinforced concrete (RC) structures by inducing a potential shift from ductile to brittle failure. This study presents a comprehensive 3D nonlinear finite element model (FEM) to systematically quantify this transition in single-story, single-bay RC frames. The model, validated against experimental data with high accuracy (<7.5% deviation), incorporates key degradation mechanisms, including rebar section loss, material property deterioration, and critically, bond-slip interface degradation. Acknowledging the idealization of uniform corrosion and monotonic loading to establish a fundamental capacity envelope, an extensive parametric study (230 simulations) was conducted. Results identified the axial compression ratio as the most detrimental parameter, causing up to a 56.7% reduction in lateral capacity, while column reinforcement was the most effective strengthening parameter, enhancing capacity by 39%. A key finding is the heightened vulnerability of higher-strength concrete to corrosion-induced capacity loss, attributed to its brittle nature exacerbating bond degradation. The primary contribution of this research is the development of a "Failure Mode Map," a novel graphical tool that quantitatively delineates the transition from a safe "Ductile-Flexural" failure zone to a dangerous "Brittle-Bond" zone as a function of corrosion level and axial load. This map provides a practical framework for structural assessment, highlighting critical thresholds beyond which conventional capacity models are non-conservative and unsafe.