Abstract: In second-order elastic analysis of the partially-braced steel frames, the initial geometric imperfections of overall frame as well as its individual member should not be neglected. So a practical second-order elastic model of a two-dimensional assemblage comprising a single column and a single beam to reflect the geometric imperfections is developed for the determination of the behavior of the steel frame columns. Using the practical model accounting for the influence parameters, the effects of the geometric imperfections can be accurately considered during the determination of the second-order elastic moments of the steel frame columns. Parametric studies are carried out to demonstrate the extent to which the involved parameters affect the behaviors of the partially-braced steel frame columns. The results of parametric analysis imply that the geometric imperfections of the partially-braced frame column may be replaced by the equivalent notional lateral load expressed as a fraction of the axial load acting on the floor.