The long columns in atrium often buckle by the non-sway mode due to the surrounding bracing frame. The objective of this study is to propose an evaluation method for the effective length factor of the long column. Evaluation formula is obtained by using the energy method, and the effective length factors are calculated taking story height ratio, flexural stiffness ratio and axial load ratio as the parameters. The accuracy is verified comparing with the exact effective length obtained using the buckling slope deflection method, and it is shown that the proposed formula is useful for the actual conditions.
