Ductile moment connections used in steel column-tree moment-resisting frames

This paper presents analytical and experimental studies on the cyclic behavior of beam-to-column moment connections used in steel column-tree moment-resisting frames. The column-tree system is joining the column-trees and link beams in the field while the column-trees are fabricated in the shop by welding stub beams to the column. The proposed ductile column-tree connections have two distinctively improved connection details which are no weld access hole detail and a widened flange of the stub beam. Nonlinear finite element analysis demonstrated the effectiveness of the improved connection details which significantly reduce the stress concentration and plastic strain demands at the beam flange groove weld. Cyclic testing of three full-scale specimens was conducted to verify the proposed connection details. All the specimens successfully developed ductile behavior with no brittle fracture by forming the plastic hinging of the beam away from the beam-column interface. The widened flange and no weld access hole details are effective in reducing the potential of brittle fracture.