## 1 Introduction  
Post-earthquake disaster surveys have shown that numerous building structures might suffer from different levels of damage after mainshock excitations, and these mainshock-damaged (MD) structures will face the threat of frequent aftershocks again, which could cause serious failures or even complete collapse [1, 2]. Especially for the widely used reinforced concrete (RC) frame structures, they easily form a weak-story mechanism during mainshocks. In that case, the concrete covers fall off, steel rebars yield, and RC frames will produce large story drift, which results in the loss of structural bearing capacity. Nevertheless, some seismic disaster investigations have found that most RC frames still have a certain residual capacity to resist collapse after mainshocks [1, 3]. For example, about 60% of RC frames could continue to be used and 32% of RC frames needed to be reinforced before use after the 2008 Wenchuan earthquake [3]. In addition, due to the uncertainty of earthquake occurrence, these mainshock-damaged RC (MD-RC) frames might be further damaged by aftershocks. Consequently, these MD-RC frames that still have retrofitting significance and they should be strengthened as soon as possible to improve their seismic capacity and prevent them from further damage during aftershocks, and then ensure the safety of people in the disaster area and reduce the waste of resources caused by the demolition of structures. In recent years, various seismic retrofitting technologies for RC frames have been proposed in order to ensure structural seismic safety [1,4], such as replacing concrete, enlarging section, bonded steel plate, external encased steel, fiber-reinforced polymer (FRP) [5, 6, 7, 8] composites or carbon/glass fiber reinforced polymers (CFRP/GFRP) composites [9, 10, 11, 12, 13], and so on. More efforts have also been devoted to the investigation of seismic performance of retrofitted structure while using either model tests or numerical modeling in such researches. The results have shown that the use of these retrofitting technologies can significantly improve the strength, stiffness, and ductility of RC frame or their members. However, there still existed some insufficiencies for these retrofitting measures and evaluation methods. For example, some conventional retrofitting measures, like replacing concrete and enlarging section, would cost much time to reach the target strength of concrete materials, and other retrofitting techniques, like bonded steel plate, external encased steel, and FRPs, are also relatively complex and time-consuming [1]. In addition, due to the time of aftershocks occurrence being usually short and frequent, quickly and effectively strengthen the mainshock-damaged structure is more helpful in reducing the further damage during aftershocks. Recently, several passive energy dissipation devices (PEDD), such as metallic dampers, friction dampers, viscoelastic dampers [4], viscous fluid dampers [14, 15, 16], and buckling-restrained braces dampers [17, 18, 19], have been widely used as global (i.e., structure-level) modification strategy [20, 21, 22]. Among these PEDDs, metallic dampers have attracted increasing attention and have become the favorite damping device for seismic retrofitting due to the following advantages, e.g., inexpensive, easy fabrication, and stable hysteretic behavior, etc. [20, 23, 24]. In addition, metallic dampers devices could dissipate the most input energy of earthquake through excellent plastic deformation potential under seismic excitation, thereby reducing seismic action on structures. The research on metallic dampers originated from the works of [PERSON] et al. [25] and [PERSON] et al. [26]. Subsequently, different types of metallic damper devices have been proposed and tested, such as shear yielding damper (e.g., shear links [21, 27, 28, 29, 30], steel shear wall damper (SWWD) [31], slit damper (SD) [32, 33, 34], dual-function metallic damper (DFMD) [35], etc.