In the structural stability design of steel structures, the effects of imperfections caused by the steel members' fabrication must be adequately taken into account. In the case of welded members, residual stresses have a substantial impact on the structural performance due to the high thermal energy input during production. In simplified design methods for steel beams, these imperfections are taken into account by assigning the members to buckling curves and the associated imperfection factors. A review of the simplified design methods and the method's structural efficiency of welded members is timely, considering the latest results of residual stresses. This paper presents a study on the lateral torsional buckling behaviour of welded steel beams and the subsequent application of the findings for simpli-fied design methods. A comprehensive numerical study analysed the load-bearing behaviour of steel beams made of S235 to S690. Residual stresses were taken into account using the residual stress approach according to current standards as well as a state-of-the-art approach. The numerical study confirmed that residual stresses influence the structural performance of members made from higher steel grades less. To take the identified effects into account for structural designs, an adjustment of the imperfection factors is proposed in this paper.