THE GENERAL BEHAVIOR AND STRENGTH OF UNBRACED MULTI-STORY FRAMES UNDER GRAVITY LOADING

The inelastic behavior of symmetrical multi-story frames under symmetrical gravity loading is described. The present state of knowledge as to the analysis of these frames is outlined. A method to compute inelastic buckling loads for multi-story frames is proposed. The results of two multi-story frame buckling tests are presented. The test specimens are three-story, single-bay, pinned-base frames. Analytical studies are conducted to examine the effects on the frame buckling loads caused by varying the structural parameters. The frames in the studies are single-bay and multi-story. They are designed on a strength basis to fail at an ultimate load equal to the beam mechanism load. The changes in the frame buckling load caused by the primary bending moments are computed and are shown to be significant. The effects on the frame buckling load caused by varying the number of stories in a frame are evaluated. The beneficial effects of partial base fixity are examined. The rotational restraints provided by the lower stories on the top stories of multi-story frames are approximated and the corresponding frame buckling loads are obtained. (Author) Rept. on proj. Frame Stability.