Abstract: The concepts ”independent bracing” and “ relative bracing” were explained, fly bracing between bottom flanges of orthogonal framed beams was a type of relative bracing whose functions were played only when the other beam had surplus stiffness and capacity. This paper suggests using stiffener to prevent distorsional buckling of frame beams on the place of 1.5 times the beam height away from the column, and the condition that no stiffener is needed is provided.