## 1 Introduction
This then makes it difficult to install such seismic control systems because they need to be added to buildings that have already been built, thereby excessively increasing the overall construction costs. There is also a possibility that these systems, once installed, may fail to achieve the desired seismic retrofitting effects for the given seismic load due to the occurrence of construction errors or buckling. If this is the case, the installed seismic control systems will not be able to effectively support and control the building, proving that they were unnecessary in the first place. Furthermore, these systems are not highly suitable for the external design of buildings, which require aesthetic features. These systems are also difficult to apply to the seismic retrofitting RC buildings, which are relatively less deformable than steel frame buildings. Thus, to overcome the disadvantages of existing seismic control systems, as described above, it is necessary to develop a system based on a completely new concept. According to necessity of a new retrofit method, new retrofit approaches have also been applied to existing RC buildings. These can reduce structural damage to existing RC buildings by concentrating seismic energy dissipation on reusable damping devices [20; 21]. More recently, studies have been carried out on hybrid damping devices with combined behavior. [PERSON] et al. proposed a visco-plastic damper which combines a displacement-dependent device and velocity-dependent device [22]. [PERSON] et al. devised a hybrid passive control device comprising a friction damper and a metalic damper [23], and [PERSON] et al. proposed buckling-restrained brace and steel frames system [24], [PERSON] et al. and [PERSON] et al. verified the seismic performance of buckling-restrained brace [25; 26]. [PERSON] et al. proposed self-centering PC reinforcement frames [27]. [PERSON] et al. proposed a vibration control technology using a passive system for curation walls and verified it analytically [28; 29; 30]. In addition, research on various reinforcement design methods to which the energy dissipation device is applied is being conducted using single-degree-of-freedom models [31; 32; 33]. In the present study, a window-type seismic control system (WSCS) using non-buckling slit dampers (NBSDs) was proposed and developed to address the disadvantages of conventional seismic control systems so that it can be effectively applied to existing RC buildings through review of previous research paper. Materials testing was also conducted to examine the material performance and energy dissipation capacity of the steel NBSD system. A full-scale two-story test frame modeled from existing domestic RC buildings with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of NBSD-WSCS, when applied to existing RC frame structures, was examined and verified, especially as to its seismic retrofitting performance. In addition, based on material testing and pseudo-dynamic test results, a restoring force characteristics model was proposed to implement the nonlinear dynamic analysis of a test building retrofitted with NBSD-WSCS. Further, based on the proposed restoring force characteristics, nonlinear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. Finally, in an attempt to commercialize this NBSD-based WSCS, nonlinear dynamic analysis was conducted on the entire RC building with non-seismic details retrofitted with NBSD-WSCS. The seismic response load-displacement characteristics, energy dissipation capacity, and degree of seismic damage based on the ductility of used members before and after the reinforcement were examined and compared to determine the corresponding seismic retrofitting performance.