This paper discusses an innovative approach to the design of planar steel frames composed of prismatic and/or non-prismatic members. The method evaluates the member stability limit states using an inelastic eigenvalue buckling analysis configured with column, beam and beam-column inelastic stiffness reduction factors derived from the ANSI/AISC 360-16 Specification. The resulting procedure provides a relatively rigorous evaluation of all member strength limits accounting for moment and axial force variations along the member lengths, non-prismatic geometry effects, general out-of-plane bracing conditions and beneficial end restraint from less-critical adjacent, unbraced segments and/or from end conditions. The approach uses a geometric non-linear pre-buckling analysis based on the AISC direct analysis method to estimate the in-plane internal forces. Given these forces, an eigenvalue buckling solution is conducted to evaluate the overall member stability. Other limit states are addressed through cross-section strength checks using the internal forces determined from the geometric non-linear load-displacement analysis. Calculations using this approach are compared with results from recent experimental tests.