Lateral displacements of moment frames at incipient collapse

This study was prompted by the need to elaborate on the lateral displacements of steel moment frames at incipient collapse. The paper presents relatively simple solutions for assessing lateral displacements of basic flexural modules, as component parts of high-rise frames, at the onset of plastic failure due to combined gravity, and lateral forces magnified by P-delta effects. These solutions are then utilized in conjunction with plastic collapse load interaction diagrams to develop families of generic displacement interaction curves for different boundary conditions. Effects of plastic hinge offsets on the ultimate performance of moment frames, has been discussed in some detail. The paper presents a number of novel concepts and formulae that have not appeared in the literature before. The results of research leading to the preparation of this article have been summarized in the conclusions. It has been shown how these findings may complement the existing literature on the subject.

► Sequence of formation of plastic hinges controls drift at incipient collapse.
► P-delta effects influence the patters and sequence of formation of plastic hinges.
► The importance of displacement calculations at incipient collapse is emphasized.
► These findings will help improve frame design in the future.
► The proposed Plastic displacement interaction charts can improve design efficiency.