AbstractThe present study investigates the elastic lateral torsional buckling resistance for steel I-beams that are strengthened with steel cover plates while being subjected to loading. A variational principle was developed for the problem by accounting for the full sequence of prestrengthening load application, strengthening process, poststrengthening load application, up to the buckling response. The variational principle was then used to develop a finite-element formulation for the problem leading to a quadratic eigenvalue problem. The formulation successfully captures the effects of prestrengthening loads, the beneficial effects due to prebuckling deformation, and the interactions between both effects. The study documents the benefit of providing transverse stiffeners to maximize the critical moment capacity attained when cover plates are used for strengthening. The study determines the locations of cover plates that would maximize the gain in critical moments in strengthening scenarios where only part of the beam span is to be strengthened. A systematic parametric study was developed to characterize the gain in elastic critical moment strength attained by cover plate strengthening and associated prebuckling deformation effects, in terms of dimensionless parameters that characterize the effects of prestrengthening load magnitude, beam span, cross-sectional geometry, length of cover plates, and cover plate cross section. Other parameters investigated include the distributions of prestrengthening and poststrengthening loading.