# Structural Performance of R-Type Steel Damper Used in Reinforced Concrete Members
## 5 Conclusions  
In this study, an R-type steel damper with a simple shape and excellent load resistance and energy dissipation capacities was proposed. A two-phase experimental study and an analytical study using FE analysis program were conducted to evaluate its structural performance. In the Phase I test, shear force was applied directly to the damper. In the Phase II test, the proposed damper was applied to an RC member to verify its structural performance. Based on the experimental and analytical studies, the following results were obtained.  
1. The shape of the proposed damper is easy to manufacture and the number and cross-sectional dimensions of the dampers can be changed freely according to the required structural performance. Tests of the structural performance of the proposed damper showed that the strength and stiffness were maintained without decreasing while a repeated load was applied five times up to the target displacement. In addition, no buckling was observed until the end of the experiment.
2. In the proposed damper, the vertical and upper horizontal members are involved in the ductile behavior and energy dissipation and the lower horizontal member is involved in strength enhancement and energy dissipation. The experimental results of the angled U-shaped steel damper showed that the strength and initial rigidity of the proposed R-type steel damper were increased by around 3.5 and 6.4 times, respectively.
3. In the Phase I test, the energy dissipation capacity of the proposed damper did not decrease during five repeated loads. In addition, the proposed damper showed an equivalent damping ratio of up to 53.4%, indicating high damping capacity. Similar characteristics were observed in the Phase II test. The Specim M2 with the proposed damper showed an equivalent damping ratio of up to 48.6%, indicating excellent damping ability.
4. The region in which energy is dissipated in the damper was similar in the FE analytical and experimental results. Most vertical and lower horizontal members of the proposed damper yielded and showed high strain in the experiment. On the other hand, the upper horizontal member yielded in some areas but contributed to the stable and ductile behavior of the damper.
5. In the Phase II test, an excellent energy dissipation capacity was measured. In the M1 specimen without the damper, excessive cracking and damage occurred because the RC member resisted the external lateral load. By contrast, the M2 specimen with the proposed R-type steel dampers showed ductile behavior without strength deterioration for a drift angle of up to 3% because the damper effectively dissipated the energy of the external lateral load. Furthermore, hardly any cracks or damage were observed in the M2 specimen. Based on the experimental results, the proposed steel damper can be applied excellently to structures as an energy dissipating device.  
[PERSON]-W.K. and [PERSON]-H.K. conceived and performed the experiments and analyzed the data and wrote the paper. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) founded by the Ministry of Education (2019R1A6A1A03032988); this research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) founded by the Ministry of Education (2018R1A2B3001656).  
Not applicable.  
The authors declare no conflict of interest.