# Experimental Study on Mechanical Behavior of Shear Connectors of Square Concrete Filled Steel Tube
## 5 Conclusions  
Through the push-out tests of 14 square CFSTs with shear connectors, limited in this study, the main conclusions are:  
1. The steel plate can effectively transmit the load between the steel tube and core concrete, and improve the co-working performance of the steel tube and concrete.
2. Comparing with single-layer steel plate specimens, the ultimate bearing capacities of the double-layer steel plate specimens are greater, and the increase has a good correlation with the spacing to height ratio \(s/h\) ratio. Further, the bigger the \(s/h\) ratio of steel plates, the greater the bearing capacity. Therefore, the \(s/h\) ratio of the steel plate must be less than 5.9 in engineering design.
3. The width to thickness ratio of the steel tube, the thickness the length of the steel plate all have significant effects on the ultimate bearing capacity and initial stiffness. The ultimate bearing capacity and the elastic stiffness increase with decreasing width to thickness ratio of the steel tube, and increasing thickness and length of the steel plate.
4. The concrete strength has a significant effect on the ultimate bearing capacity. Further, with concrete of greater strength, the ultimate bearing capacity is also greater.
5. The welding condition of the steel plate has no effect on the ultimate bearing capacity. Hence, if the shear connectors are designed to have no shear failure on the steel plate or no local bucking on the steel tube, single-sided welding can be used in real-life engineering projects, which reduces the construction tasks.
6. In the case of the same amount of steel, the bearing capacity of the steel bar specimen with the same number of layers is 87% greater than that of the steel plate specimen. However, the descending part of the steel bar specimen is steeper than that of the steel plate specimen after reaching the ultimate bearing capacity.
7. The calculation method is proposed for the ultimate bearing capacity, and the calculated capacities are in good agreement with the test data.  
**Acknowledgments:** This work was supported by a National Natural Science Foundation of China grant funded by the Chinese government. (No. 51408017). The support is greatly appreciated. Also, the suggestions on the design of the specimens from Prof. [PERSON] in Kyushu University in Japan are highly appreciated.  
**Author Contributions:** [PERSON] designed the tests and analyzed the data; [PERSON] performed the tests, analyzed the data and prepared the manuscript; [PERSON] proposed the topic of this study, analyzed the data and prepared the manuscript; [PERSON] and [PERSON] participated in the tests and analyzed the data.  
**Conflicts of Interest:** The authors declare that there is no conflict of interests regarding the publication of this paper.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Specimen** & \(P_{\textit{LASP}}\) **(kN)** & \(P_{\textit{LACI}}\) **(kN)** & \(P_{\textit{LASP}}\)/\(P_{\textit{LACI}}\) & **Failure Mode** \\ \hline P8-8-0-120 & 680.2 & 674.9 & 1.008 & A \\ P8-4-150-120 & 527.9 & 505.4 & 1.044 & A, B \\ P8-6-150-120 & 709.3 & 679.1 & 1.044 & A \\ P8-8-150-120 & 921.0 & 913.8 & 1.008 & A \\ P8-14-150-120 & 2284.0 & 2186.8 & 1.044 & A \\ P4-8-150-120 & 694.5 & 615.5 & 1.128 & A \\ P12-8-150-120 & 1401.6 & 1215.4 & 1.153 & A \\ P8-8-100-120 & 766.0 & 742.4 & 1.032 & A \\ P8-200-120 & 1342.9 & 1349.8 & 0.995 & A \\ P8-8-150-120\({}^{\#}\) & 1050.5 & - & - & A \\ P8-150-80 & 833.0 & 746.1 & 1.116 & A \\ P8-8-150-150 & 1250.0 & 1021.7 & 1.223 & A \\ P8-150-120\({}^{\#}\) & 1137.3 & 1114.9 & 1.020 & A \\ B10-8-150-174 & 1725.5 & - & - & A \\  & the mean value: & 1.068 & & \\ \hline \end{tabular} Note: symbol \({}^{\#}\) indicates single-sided welding, others were double-sided welding; symbol \({}^{\bullet}\) indicates the infill concrete grade was C40, others were C30.  
\end{table}
Table 5: Failure mode and comparison of calculated ultimate bearing capacities and test data.