Elastic Stability Of Frames Considering The Inter-Story Interaction

Through an analysis of a simple two-story frame, this paper revealed that the assumptions used in current effective length method led to unrealisticdistribution of beam restraints among the connected columns. With three assumptions of the conventional effective length approach discarded, a newapproach is proposed by which column effective length consideringinter-story interaction can be obtained in un-braced two-story or three-story frames. A quadratic equation with one variable for two-story frames and a cubic equation with one variable for three-story frames are derived from which the rotational restraint provided to each column may be solved and the effective length factors can then be determined by the traditional formula or tables. For frames of more than 3 stories, the weakest story is first selected and a three-story sub-assemblage including the weakest column is taken out, and the proposed method is applied, the effective length of the weakest column is thus obtained, the effective length of the remaining columns are computed through a pre-defined relations. Because the sub-assemblage included beams at far ends of the columns above and below the column under consideration, the far end condition (hinged or fixed) may be considered easily.