In the design of steel structures, the imperfections arising during the steel members' fabrication must be considered. These imperfections are divided into geometric imperfections, and structural imperfections, such as material inhomogeneities and residual stresses. In the case of welded members, residual stresses have a substantial impact on the structural behaviour due to the high thermal energy input during production and the consequent high magnitudes of residual stresses. In simplified design methods for steel members, these imperfections are taken into account by the assignment to buckling curves and the associated imperfection factors. Therefore, with an advanced consideration of residual stresses, an evaluation of the simplified design methods for welded members is reasonable. This paper presents investigations on the stability behaviour of welded steel members and the subsequent application of the findings for simplified design methods. In a comprehensive numerical study, the load-bearing behaviour of steel columns and beams with varying geometrical dimensions made of S235 to S690 was analysed. Residual stresses were taken into account using a state-of-the-art approach that appropriately considers both fabrication methods in terms of thermally cut or non-thermally cut plates as well as the steel grade. The numerical study showed a beneficial effect on the structural behaviour of members of higher steel grades, which resulted from reduced influences of residual stresses. To take the identified effects into account, an adjustment of the imperfection factors in the simplified design methods was worked out and evaluated. Thus, current verification methods with slight adaptions result in a more economical design of welded steel structures.