Cyclic behaviour of unreinforced and rib-reinforced moment connections

This study investigates the cyclic behaviour of the beam-to-column welded moment connections used in steel moment-resisting frames. Two unreinforced welded connections were tested initially to elucidate the behaviour and failure mode. Test results showed that both specimens failed by the brittle fracture of the beam flange, initiated from the root of the weld access hole. Nonlinear finite element analysis was used to identify the causes of the failure. The stress concentration in the weld access hole region has the potential to cause the beam flange to fracture. Analytical results also demonstrated that reinforcing the connection with a single rib can reduce the concentration of stresses at the root of the weld access hole. Further tests of two specimens whose beam flanges were each reinforced by a single rib revealed that the single rib effectively prevents beam flange fracture in the weld access hole region.