## 5 Conclusions  
In this study, the NoWS system, which uses CFST frames, has been proposed to improve the existing seismic retrofit method for RC moment frame structures. To assess the effects of seismic retrofitting, one non-retrofitted ERC moment frame specimen and one retrofitted specimen using NoWS were manufactured, and a full-scale cyclic loading test was conducted. The main conclusions of the study are as follows:  
(1) All test specimens had cracks, which were observed at the end of columns when the drift ratio reached 1%, and numerous cracks in the beam-column joints and columns developed at subsequent drift ratios. As the lateral load increased, initial cracks propagated and shear cracks in the columns increased, resulting in concrete spalling; the experiment was terminated at a drift ratio of 2.5%. In the ERC specimen, the column rebar buckled as the width and the number of cracks increased rapidly after shear cracks were observed in the columns. In the NoWS cracks, unlike in the ERC, only a few shear cracks could be observed. Bolt loosening, deformation and separation of steel channel were not observed. (2) In ERC and NoWS specimens, the applied lateral loads reached maximums of 332 kN and 924.32 kN in the positive direction, respectively, and \(-\)314.2 kN and \(-\)863.17 kN in the negative direction, respectively. This confirmed that retrofitting with the NoWS system increased the resistance to lateral loads by approximately three times compared to the ERC. The NoWS system can therefore be considered an effective seismic retrofit method for increasing the strength of existing RC frames. (3) In columns, the concrete of the ERC specimen exceeded the ultimate compressive strain when initial cracks were observed. In the longitudinal steel and hoop, all of the specimens yielded at 1.5% and 2% drift ratios, respectively. For the NoWS specimen, the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Drift Ratio (\%)**} & \multicolumn{2}{c}{**Energy Dissipation (kN-mm)**} & \multicolumn{2}{c}{**Ratio of NoWS to**} \\ \cline{2-4}  & **ERC** & **NoWS** & **the ERC** \\ \hline
0.1 & 190.49 & 324.47 & 1.70 \\
0.25 & 436.75 & 729.5 & 1.67 \\
0.5 & 1398.96 & 2386.22 & 1.71 \\
0.75 & 3575.80 & 6423.29 & 1.80 \\
1.0 & 7532.15 & 14,189.65 & 1.88 \\
1.5 & 15,679.67 & 30,604.35 & 1.95 \\
2.0 & 29,543.71 & 60,392.80 & 2.04 \\
2.5 & - & 109,043.16 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Energy dissipation capability in each specimen. Figure 14: The difference between energy dissipation at the various drift ratios. strain increased gradually after the yield of the rebar and final failure occurred, whereas the strain in the ER specimen increased dramatically. This demonstrated that the NoWS retrofit method could evenly distribute the stress concentrated on a specimen column and increase the resistance capability for lateral load. (4) The NoWS system was found to have twice the effective stiffness compared to the non-retrofitted ERC specimen. The effective stiffness of each specimen reached 50% of its initial stiffness at the 0.75% and 1.5% drift ratios, respectively. This confirmed that the NoWS system retrofit method could increase the effective stiffness of a specimen. The NoWS system had twice the energy dissipation capability of the non-retrofitted ERC specimen. (5) Experimental results were very similar to the results of previous studies which dealt with welded connections, which indicated that the NoWS system was connected well, without bolt loosening. Thus, the seismic retrofit method by the NoWS system can address many disadvantages of welding, and is effective in enhancing specimen strength, making it effective in improving the seismic capacity by dissipating seismic energy significantly compared to ERC structures. Conceptualization, K.M.R. and Y.H.L. ; methodology, K.M.R., M.S.K. and D.-S.H. ; resources, D.-S.H. ; validation, Y.H.L. ; formal analysis, K.M.R. and M.S.K. ; investigation, K.M.R. and Y.H.L. ; writing--original draft preparation, K.M.R.