## 1 Introduction
However, considering conventional vibration control systems are typically installed at the building construction stage, they involve excessive costs when installed in existing buildings for seismic reinforcement because it is difficult to install them at a later stage; moreover, the reinforcement effect may not be satisfactory because of a vibration control system installation error for the expected level of the seismic load, and buckling may occur. It is also difficult to apply them for the seismic reinforcement of R/C buildings, which have a relatively small deformation capacity compared to steel frame buildings; in particular, they are prone to bending deformation under out-of-plane loads. Therefore, these issues highlight the need to develop a new vibration control system that supplements and overcomes the above-mentioned shortcomings of conventional vibration control systems. [PERSON] et al. [24] developed superelastic shape memory alloy wire dampers and verified their performance through analytical studies, and [PERSON] et al. [25] performed FEA of metal shear panels and R/C structures to which metal shear panels were applied. Performance was verified through full-scale tests. [PERSON] [26] conducted research on a link that acts as a sacrificial fuse by dissipating seismic energy among the key components of EBF. [PERSON] et al. [27] verified the self-centering performance of buildings when analyzing the parameters of shape memory alloy braces and applying them, and [PERSON] et al. [28] conducted an experimental analysis of low-yield-point steel shear panel dampers. [PERSON] et al. [29] conducted an analytical study on buildings using continuous energy-dissipative steel columns. In addition, a variety of studies have been conducted on friction dampers rather than just metal dampers. [PERSON] et al. [30] presented a novel friction damper device and conducted research on the type and frequency influence of friction pads, and [PERSON] et al. [31] performed experiments and analysis by applying the friction damper as diagonal bracing. [PERSON] et al. [32] proposed a friction damper with two slip loads and verified the seismic performance through nonlinear dynamic analysis. [PERSON] et al. [33] verified the performance of the self-centering rotational friction damper that can provide both energy dissipation as well as self-centering characteristics through experimentation and FEA. [PERSON] et al. [34] developed a self-centering damper that exploits the shape memory alloy bolts and variable friction mechanism and verified its performance through experiments and FEA. This study proposed a novel V-bracing system equipped with a laterally layered friction damper (LLFD), which can supplement the shortcomings of conventional vibration control systems and is applicable to existing R/C buildings. The material performance and energy dissipation capacity of the LLFD were evaluated through a material test. In addition, pseudo-dynamic testing was conducted on two-story frame specimens based on an existing R/C building with non-seismic details to verify the seismic retrofitting effect of applying the LLFD V-bracing system to existing R/C frames, i.e., the restoring force characteristics, energy dissipation capacity, and seismic response control capacity. Based on the results of the material test and pseudo-dynamic test, restoring force characteristics were proposed for the non-linear dynamic analysis of a building (frame specimen) retrofitted with the LLFD V-bracing system. A non-linear dynamic analysis was conducted based on the proposed restoring force characteristics, and the results obtained were compared with the pseudo-dynamic test results. Finally, for evaluating the commercialization potential of the LLFD V-bracing system, a non-linear dynamic analysis was conducted on the existing R/C building with non-seismic details retrofitted with the system.