Steel rigid connections are vulnerable to seismic damage due to low rotational capacity. Slit dampers offer an effective solution, but previous studies primarily focused on shear-dominant applications in bracing systems. This experimental study investigates slit dampers installed in the beam bottom flange zone of rigid moment connections, where they resist combined shear and considerable flexural moment. Twelve dampers with four geometric patterns (straight, hexagonal, elliptical, and dumbbell) and three thicknesses (4, 5, and 6 mm) were tested under cyclic loading (FEMA 350 protocol) and compared with a reference welded connection. Furthermore, the interactive effects of geometric shape and plate thickness on key seismic performance parameters—including effective stiffness, energy dissipation, and ductility—were systematically evaluated.

The elliptical damper with 6 mm thickness exhibited the best performance: effective stiffness of 5.0 kN/mm at 50 mm drift (2.1 times that of dumbbell type), cumulative energy dissipation of 2900 KN.mm (35% higher than dumbbell), and the most stable hysteresis. The reference connection lost 68.5% of its initial stiffness by 50 mm drift, showing brittle behavior. Increasing thickness from 4 to 6 mm significantly enhanced stiffness and energy absorption in all geometries. The elliptical shape, with uniform stress distribution and no sharp corners, is introduced as the optimal geometry, concentrating damage in the replaceable fuse element and enabling post-earthquake reparability. The findings demonstrate that the simultaneous selection of optimal shape and appropriate thickness can substantially improve connection performance, offering a viable alternative to traditional welded connections.