Frame Response Considering Plastic Panel Hinges

The AISC-LRFD Specification designates connections as fully restrained (FR) or partially restrained (PR). Only a beam-to-column connection that has sufficient rigidity to hold the original angles between members unchanged may be considered as Type FR. The quantification of this requirement has been left to the judgment of the structural engineer. One major source of deformation that occurs in FR connections is shear deformation of the column panel zone when beams frame to the column flange(s). Connections that have traditionally been assumed to be fully restrained are, in fact, only partially restrained because they permit relative rotation between the beam and column.