In this study, a theoretical analysis is presented for estimating the in-plane large displacement elastic-plastic stability behavior of steel frames having prismatic and non-prismatic members with end gusseted plates subjected to increasing static loads. The analysis adopts the beam-column approach and models the structural members as beam-column elements. The formulation of the beam-column element is based on Eulerian approach allowing for the influence of the axial force on bending stiffness. In this study, the effect of gusseted plate is taken with the modified stability and bowing functions for gusseted plate with prismatic and non-prismatic members (Tapered and Non-linearly tapered).The post-buckling analysis is studied, and the incremental load control with different load increment strategies and the modified Newton-Raphson method with different iterative strategies are used to obtain the complete load-displacement curve. Furthermore, the determinant technique is used to detect the intersection of load limit points.As a result, the beam column approach can be used in the analysis of plane frames with and without gussets and with any varying section. The ultimate load capacity can be increased with gusset-plate members, and with tapering the prismatic members for the same weight, and then the displacement can decrease