# Seismic Performance of Dam Piers Retrofitted with Reinforced Polymer Cement Mortar
## 4 Results and Discussion
### Reinforcement Effect by Structural Characteristics of Dam Pier  
Figure 35 shows the classification of dams in the area of the graph near the four dams discussed in the previous section, using the amount of reinforcing bars in the existing cross-section and the slenderness ratio of the column shape, and Table 5 shows the natural period of each dam. It was found that the TYPE-C dam shows the least damage and has the shortest natural period; thus, the TYPE-C dam has higher rigidity than the other dams. As shown by arrow (A) in Figure 35, TYPE-A and TYPE-D have a smaller slenderness ratio than other dams, but the amount of existing reinforcing bars is small, and the load-bearing performance is also lower than that of other dams. Therefore, the reinforcing effect of the PCM method is clearly shown for TYPE-A and TYPE-D. On the other hand, although the TYPE-B dam has a larger amount of reinforcing bars than the TYPE-C dam, the slenderness ratio of the column shape is large, and the additional mass is also larger than that of the TYPE-C. Therefore, the reinforcement effect of TYPE-B is higher than that of TYPE-C. In summary, the reinforcement effect of the SRS method is likely to be obtained in dams with a long natural period.  
Figure 34: Strain distribution of existing reinforcing bars at peak displacement in wave B: (**a**) TYPE-A; (**b**) TYPE-B; (**c**) TYPE-C; (**d**) TYPE-D.  
Figure 36 shows that the five dams in the red dashed circle are the groups that are most likely to be reinforced by RPCM because of their insufficient amount of reinforcing bars. To confirm the effect of the RPCM reinforcement, TYPE-B' having a lower amount of existing reinforcing bars than TYPE-B (shown in Figure 36) was modeled, and its elastic-plastic behavior under earthquake conditions was calculated. Specifically, the cross-sectional area of the rebar elements in the TYPE-B FE model was uniformly reduced, and the total number and spacing of reinforcing bars did not change in TYPE-B'.  
Figure 36: Classification of dams by slenderness ratio and amount of reinforcing bars (Added TYPE-B’).  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Natural Period (s)** & **TYPE-A** & **TYPE-B** & **TYPE-C** & **TYPE-D** \\ \hline Primary mode & 0.353 & 0.482 & 0.175 & 0.243 \\ \hline Secondary mode & 0.153 & 0.139 & 0.102 & 0.076 \\ \hline
3 rd mode & 0.0973 & 0.120 & 0.0435 & 0.059 \\ \hline
4 th mode & 0.053 & 0.103 & 0.036 & 0.051 \\ \hline \end{tabular}
\end{table}
Table 5: Natural period of each dam.  
Figure 35: Classification of gravity dams when viewed in terms of the amount of existing reinforcing bars and slenderness ratio of dams near the area where the four dams exist.  
Figure 37 shows the displacement-time history of TYPE-B' under seismic waves A and B, respectively. From these results, it can be seen that the maximum displacement and residual displacement of TYPE-B' are significantly reduced owing to the reinforcement effect of the RPCM. In addition, it was confirmed that reinforcement by RPCM is sufficiently effective only if an area of approximately 30% of the entire cross-section of the column is reinforced to reduce the residual displacement.  
As a result, it was concluded that the RPCM reinforcement method is very effective for existing aged dam piers with insufficient rigidity.