A mechanics-based framework for assessment and repair of corroded steel beams with section loss and disrupted load paths

Corroded steel beams are commonly assessed using reduced cross-sectional properties; however, such approaches cannot reliably capture localised deterioration, perforations, or corrosion-induced disruption of load-transfer mechanisms. This study proposes an elastic-first mechanics-based framework that integrates corrosion classification, behavioural zoning, mechanism-admissibility checks, and mechanism-specific limit-state evaluation. The framework links measured residual geometry and damage location to competing responses including flexural yielding, shear degradation, web bearing, web crippling, Vierendeel action, web-post instability, ligament rupture, and residual frame-type response. Resistance is evaluated at the onset of yielding or instability, providing a physically interpretable lower-bound estimate suitable for structural assessment and repair prioritisation. Representative comparisons with conventional reduced-section and established opening-specific methods showed that the framework recovered conventional predictions where the original load path remained valid, while identifying alternative governing mechanisms where local support behaviour or opening interaction controlled the response. Validation used 35 results from published experimental datasets covering support-region instability, opening-controlled response, ligament failure, flexural degradation, and global instability. For 16 onset-level cases, the mean experimental-to-predicted resistance ratio was 1.12 with a coefficient of variation of 5.2%; for 19 comparisons against ultimate resistance, the corresponding values were 1.18 and 17.3%. The larger scatter in ultimate-load comparisons was associated principally with post-yield redistribution and post-buckling reserve, which are outside the intended elastic-first scope. The framework therefore provides a transparent, inspection-oriented procedure for identifying the governing onset-level mechanism and prioritising structural assessment and repair.