Moment redistribution caused by beam fracture in steel moment frames

This paper presents an analytical study on static moment redistribution and resultant reduction of lateral resistance caused by sudden beam fractures in steel moment frames. A numerical example is presented for a simple multi span frame, and the step-by-step processes of beam fractures, moment redist ribution, and loss in resistance under statically increasing lateral deflec tion are examined. The mechanism of moment redistribution is interpreted us ing the three-moment equations, and the possibility of sequential fractures in the course of static moment redistribution is investigated. A sudden fr acture of a beam changes moment distribution rather locally, particularly w hen plastic hinges are already formed in beams by the time of the fracture. Sequential fractures are less likely to occur during static moment redistr ibution when rotations corresponding to fracture are large (to simulate fra ctures after significant plastification) and vary from plastic hinge to pla stic hinge (to allow for the random nature of fractures). It should be care fully noted that the above observations are applicable for static moment re distribution, and do not necessarily represent the effects of beam fracture s on dynamic responses.