This study presents a design method and detailing for seismic retrofitting of moment connections in box and wide-flange columns. The proposed connection attaches each beam flange to the column flange using T-shaped Stiffeners, and the top and bottom cover plates are eliminated due to poor welding quality. The seismic performance of the proposed connection as a fully rigid moment connection is evaluated with high accuracy using the finite element method. Then, energy dissipation is investigated by forming a plastic hinge in the beam and out of connection region, considering the von Mises stress distribution criterion and equivalent plastic strain. The results of the hysteresis curves show that the specimens reached a story drift angle of 6% radians before experiencing a 20% reduction in strength, and the proposed connection is acceptable as a fully rigid moment connection for use in special moment frames according to the AISC 341-22 code.