Abstract: A notional load for flexural bracing frames is proposed to avoid determining the effective length of columns in the design of steel structures. Notional loads are applied on the frame stories, with second-order elastic analysis, considering the material nonlinearity, residual stress and initial geometric imperfections, a flexural bracing frame model under a variety of geometry and load conditions and a series of the ultimate bearing capacity are analyzed, and then the notional load coefficient and the approximate formula of the notional load are proposed. It is found that the results with finite element results are in a good agreement no matter with or without horizontal load, and no matter a uniform cross-section or a variable cross-section.