Effect of localized damage on lateral–torsional buckling capacity of continuous steel I-beams

This paper investigates the Lateral-Torsional Buckling (LTB) resistance of continuous hot-rolled steel I-beams with localized cross-sectional damage. Due to the alternating sagging and hogging moment regions, continuous beams exhibit spatially varying compression flanges and buckling mechanisms that differ fundamentally from those of simply supported beams. An integrated experimental-numerical program was conducted. Six continuous beam specimens with bottom flange loss, web openings, and combined defects were tested under four-point bending. Initial geometric imperfections were measured to establish maximum out-of-straightness amplitudes, which were subsequently used to scale the first elastic buckling mode shape in the finite element models. A large-scale parametric study involving numerous simulations was then developed to assess the effects of damage location, beam slenderness, damage severity, and sectional thickness reduction. The results reveal that the beam's capacity is most sensitive to defects located in high-bending-moment regions. A significant “slenderness convergence effect” was observed, where short beams exhibited severe capacity reduction (approximately 42%) dominated by cross-sectional yielding, while slender beams were less sensitive due to global elastic buckling governance. Based on these findings, simplified design formulas for the load reduction factor β L are proposed following a lower-bound envelope approach. This method enables the rapid and safe estimation of the residual capacity of locally damaged continuous beams, a scenario that is not currently addressed in existing design standards.