AbstractTo increase the energy dissipation capacity and deformation capacity of the beam-column connections, and save space for realizing more architectural functions in the frame structure, a new type of metallic damper is developed that is installed inside the connection area and is convenient to assemble and disassemble. The components and construction procedure of the damper are explained, and according to the analysis on the force transfer mechanism of the beam-column connections equipped with this damper, their deformation capacity and energy dissipation can be greatly improved. To verify the cyclic behavior of the new rotational metallic damper, an experimental study is conducted and the failure process and hysteretic behavior of the test specimens with different damping materials are reported. The load-deformation behavior, bending moment capacity, overstrength, and energy dissipation capacity are analyzed, and it is found that the specimens made of low-yield-point steel BLY160 and high-strength steel Q345GJ have both demonstrated a ductile failure pattern and stable and energy-dissipative hysteretic behavior. The rotational capacity of the damper can be as large as 0.08, and the specimen composed of BLY160 presents a significant strain-hardening phenomenon as its overstrength factor has exceeded 2.0. Both specimens have excellent energy dissipation capacity under large deformations, but the specimen made of BLY160 is more energy-dissipative under small deformations as its yielding strength is much low than Q345GJ. Meanwhile, formulas to calculate the bending moment capacity of the damper are deduced. Subsequently, a numerical investigation is carried out to establish an accurate finite-element model for simulating the cyclic behavior of the damper. Based on the proposed numerical model, the influence of shear or axial forces induced by the connection on the damper is evaluated, and an optimization procedure is conducted to further increase the seismic performance of the rotational damper. In the end, the typical frame substructures with a traditional beam-column connection, with typical metallic dampers, and with the proposed rotational damper are analyzed, and the results show that the rotational damper could more effectively improve the deformation capacity and energy dissipation efficiency of the substructure compared with other dampers. Then, nonlinear time-history analysis is performed on a case-studied structure with and without the rotational damper, and the results prove that the new rotational metallic damper can significantly improve the seismic performance of the structure.