## 5 Conclusions  
A new type of composite column, which is referred to as a composite concrete column in which GFRP is externally wrapped over several GFRP square tubes to form a multi-cavity GFRP tube, and then concrete is poured inside, was introduced and tested under compressive loading. The failure modes, axial load-displacement relationships, and axial load-strain responses were determined. The failure modes and mechanical characteristics were investigated. To determine the overall mechanical behavior of the novel composite columns, finite element models were proposed. The corresponding major conclusions are summarized as follows:  
1. The failure mode of the composite GFRP-confined concrete square column was internal concrete collapse. The GFRP tube reached the load capacity before it ruptured, the composite column expanded peripherally, the externally wrapped GFRP fiber broke successively, and the specimen exhibited ductile failure;
2. Based on a comparison of the load-strain relationship curves of the GFRP tube and externally wrapped GFRP strips, it is evident that the two are highly consistent, thereby indicating that the externally wrapped GFRP strips and purtuded GFRP tube could undergo cooperative deformation under the action of axial loading, and the impact of bond slip between the materials was negligible on the mechanical properties of the structure;
3. An increase in the number of externally wrapped GFRP fiber layers or a reduction in the clear spacing of GFRP strips could improve the load capacity of the composite columns. The GFRP numerical model adopts a linear elastic model, and the bearing capacity of the specimen can be predicted by the tensile strength of GFRP in the model, which is in good agreement with the experimental results. However, in order to obtain more accurate results in subsequent studies, the failure criterion of FRP should be introduced to improve the model;
4. Compared with the performance of the entirely wrapped GFRP tube, the load capacity of the specimens in the W50S40 group declined by 9.8%, while the peak efficiency of the GFRP strips increased by 50%. The adoption of proper GFRP layers and strip intervals not only facilitates convenient construction, but also ensures that the bearing capacity of the composite column is appropriate and that the material properties of GFRP are fully utilized. Conceptualization, Y.Q. ; methodology, J.L., Y.Q. and X.W. ; software, J.L. and X.W. ; validation, Y.Q. and J.L. ; formal analysis, J.L. ; investigation, J.L. ; resources, J.L. and X.W. ; data curation, J.L. and Y.L. ; writing--original draft preparation, J.L. and Y.L. ; writing--review and editing, J.L. and Y.Q. ; visualization, J.L. ; supervision, Y.Q. and J.L. ; project administration, Y.Q. ; funding acquisition, Y.Q. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Specimen Number** & \
\begin{tabular}{c} **GFRP Peak Efficiency** \\ **N/mm2** \\ \end{tabular} &
\begin{tabular}{c} **Improvement Ratio of the** \\ **Peak Efficiency of GFRP** \\ \end{tabular} \\ \hline W50S0-2 & 2.71 & - \\ W50S40-2 & 4.09 & 51\% \\ W50S60-2 & 4.57 & 69\% \\ W50S85-2 & 5.28 & 95\% \\ W50S0-4 & 1.44 & - \\ W50S40-4 & 2.16 & 50\% \\ W50S60-4 & 2.45 & 70\% \\ W50S85-4 & 2.78 & 93\% \\ W50S0-6 & 1.00 & - \\ W50S40-6 & 1.50 & 50\% \\ W50S60-6 & 1.70 & 70\% \\ W50S85-6 & 1.93 & 93\% \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Improvement ratio of the peak efficiency of GFRP strips. **Funding:** This research was funded by the National Natural Science Foundation of China (grant number 51778286). **Institutional Review Board Statement:** Not available. **Informed Consent Statement:** Not available. **Data Availability Statement:** Not available. **Acknowledgments:** The experiment was conducted in the Nanjing Tech Civil Engineering Laboratory. I would like to thank my professor and our research team workers for their help.