In plane buckling of frames with laced built-up members

For assessment of portal frames with laced built-up members the first order internal forces and the equivalent column method are the mostly used. If the distance between neighboring nodes is used as the buckling length of the chord in the equivalent column method the second order effects with only the bow imperfection between nodes are taken into account. For frames sensitive to buckling in a sway mode the second order effects on structures with initial sway imperfection should be taken into account. In portal frames with the laced compression columns the sway imperfection should be also applied and the second order in frame analysis should be performed. The simplified procedure to check the additive forces, which arise in the chords as the second order effect are proposed.