Stability of Unbraced Single-Bay Multistory Frames

The elastic critical sum of vertical loads acting on an unbraced symmetrical frame is very nearly constant and is irrespective of the ratio of load carried by each column. Thus, in the elastic stability analysis of multistory frames, it is recommended that the variations of the axial forces in the columns produced from wind or other lateral forces be neglected. It is found that the sway buckling loads decrease materially when such deformations are included for frames having bigger number of stories. The maximum decrease in the sway buckling loads is noticed for multistory frames having constant column sections, equal beam stiffnesses, same story heights and which are loaded only at the top. As the span of the frame gets smaller with respect to the height of columns, the values of the buckling loads as obtained by multistory frame analysis are very nearly the same as those produced from battened column analysis.