# Performance Evaluation of Reinforced Recycled Aggregate Concrete Columns under Cyclic Loadings
## 5 Conclusions  
Previous studies on evaluating the seismic performance of concrete columns made with RCAs are still not often seen. These columns have many potential applications in areas with seismic design requirements. With the aim of addressing this significant gap, this research presents a simple, yet practical and efficient, numerical method implemented in the SeismoStruct software to provide an in-depth understanding of the seismic performance of RRC columns. The findings from this study support the following conclusions:  
1. The lateral load-carrying capacity of RRC columns using the AWM generally reduces (up to 10%) with an increase in the RCA replacement percentage, whilst this trend is reversed when the ETWM is used.
2. Increasing the steel strength is advantageous to the gain in lateral strength of the RRC column, but this leads to a reduction in ductility. Similar two-edged results are also observed when increasing the area ratio of steel reinforcement.
3. Bi-directional loading has a negative influence on the lateral load-carrying capacity, but it has a positive influence on the ductility of RRC columns.
4. The steel strength and some well-recognized structural factors (i.e., the shear-span ratio, the area ratio of steel reinforcement, and the axial load ratio) are identified by the GRA method as the most essential parameters affecting the seismic performances of RRC columns, with the grey relational entropy density, \(\gamma\), ranging from 0.80 to 0.87.
5. The sensitivity of RCA percentage on the seismic performance of RRC columns is quite modest compared to those of the four factors listed in (4); however, quality and percentage of RAC still should be well-controlled in seismic design of RRC columns.  
Overall, it can be said that the use of the RRC columns in seismic regions is generally viable. Those green columns can be properly seismically designed with confidence despite some of the deleterious aspects. However, further studies are still needed, such as determining the minimum longitudinal and transverse steel ratios used in RRC columns, to suppress any negative effects caused by the incorporation of RAC. More experimental data are also called for to investigate the variability of the seismic performance of RRC columns and, finally, to determine their seismic reliability.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Performance**} & \multicolumn{3}{c}{**Grey Relational Entropy Density \(\gamma_{i}\)**} \\ \cline{2-6}  & \(r\) & \(L/h\) & \(f_{y}\) & \(\rho_{s}\) & \(n\) \\ \hline \(P_{u}\) & 0.62 & 0.87 & 0.86 & 0.86 & 0.85 \\ \hline \(\mu\) & 0.58 & 0.84 & 0.83 & 0.83 & 0.80 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Ranking results of grey relational evaluation.  
**Funding:** The authors would like to gratefully acknowledge research grants from the National Natural Science Foundation of China (Project Nos: 51708289 and 51608435), Postdoctoral Science Foundation of China (Project No: 2017M611796), Fund of State Key Laboratory of Subtropical Building Science of China (Project Nos: 2017 KC18, 2018 ZB34 and 2019 ZB22), Special Fund for Energy Conservation of Guangzhou (Project No: J-2016-01) and Fundamental Research Fund for the Central Universities (Project No: 2018 ZD43).  
**Conflicts of Interest** The authors declare that there is no conflict of interest regarding the publication of this paper.