Shaking table tests and analysis of the seismic behavior of external steel frames with viscoelastic nodal dampers

This study proposes a novel external steel-frame system equipped with viscoelastic nodal dampers for improving the seismic performance of reinforced concrete (RC) structures. The nodal dampers utilize viscoelastic materials to dissipate seismic energy through hysteretic shear deformation, thereby reducing the dynamic response of the main structure. An external steel frame is connected to the original RC frame through these dampers, forming an integrated load-bearing and energy-dissipating system. A series of shaking table tests were conducted on two models: the original RC frame and the retrofitted structure incorporating the external steel frame with viscoelastic nodal dampers. The tests investigated the acceleration and displacement responses under different seismic excitations, with peak ground accelerations ranging from 0.2 g to 1.0 g. The results demonstrate that the proposed system significantly enhances stiffness and energy dissipation capacity, effectively reducing floor acceleration and inter-story drift. Under moderate earthquakes, the external steel frame increases the overall stiffness, while under strong ground motion, the viscoelastic nodal dampers dominate energy dissipation. The maximum reduction in acceleration response reached 64%, and inter-story displacement was reduced by up to 52.4%. These findings confirm the system's ability to provide both seismic strengthening and damping, offering a practical and sustainable solution for the seismic retrofit of existing RC structures.