## 7 Conclusions  
Uniaxial tensile and high-stress repeated tension and compression tests of 32 APC connectors with different lapping lengths were carried out. Analysis of the mechanical properties of these grouted sleeve lapping connectors was conducted. The following conclusions were drawn based on this research. 1. There were two failure modes of the APC connector specimens under uniaxial tension: steel bar tensile failure and steel bar pull out. There were three failure modes of the specimens under high-stress repeated tension and compression: steel bar tensile failure, steel bar pull out, and steel bar bending. 2. The bearing capacity of specimens was strengthened after repeated high-stress tension and compression, so the ultimate bearing capacity increased compared with specimens under uniaxial tension. Because of anti-deflection measures, the bearing capacities of specimens without anti-deflection measures were lower than those of specimens with anti-deflection measures. 3. When the connector was broken via the steel bar being pulled out under uniaxial tension, the effects of the lapping length and anti-deflection measures on the ductility of the specimens were not evident under repeated tension and compression. As the steel bar was hardened and the cracks of the grout were fully developed under repeated tension and compression loading, the yield displacement \(\delta_{y}\) of the specimens increased, and the ductility of the specimens was less than that of the specimens under uniaxial tension. 4. The values of the residual deformation \(u_{0}\) and \(u_{20}\) decreased with the increase in the lapping length. The stiffness values before yielding of the specimens with anti \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Data Source**} & \(d\) & \(t\) & \(D\) & _f_\({}_{1}\) & _l_\({}_{\text{cn}}\)/d_ & _l_\({}_{\text{low}}\)/d_ \\  & **(mm)** & **(mm)** & **(mm)** & **(MPa)** & **(MPa)** & _\(\omega\) = 0.85_ & _l_\({}_{\text{low}}\)/d_ \\ \hline Value from this test & 20 & 3 & 70 & 4.12 & 13 & About 8–10 \\ Value from [PERSON]’s test & 18 & 3 & 70 & 4.63 & 11 & 10.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison between the test and calculated values of the critical lapping length of specimens with grouting defects. deflection measures were higher than those without anti-deflection measures, whereas the values of the residual deformation \(u_{0}\) and \(u_{20}\) were lower. 5. Under uniaxial tension and repeated tension and compression (only the final tension process) loading, the longitudinal compressive strain, and the hoop tensile strain near the steel bar side of the middle section of the sleeve decreased with the increase in the lapping length of the sleeve under the ultimate load. After repeated tension and compression loading, the longitudinal strain in the middle of the sleeve changed from compression to tension under tension and from tension to compression under compression with the increase in the lapping length. 6. When the lapping length was small, the sleeve was subjected to longitudinal compression in the early stage and tension in the late stage, which agreed with the test results. The distribution of the bonding stress of the steel bar and the sleeve changed with the increase in the lapping length, which needs further research. 7. The correlation between the variables and the bonding strength of the APC connector was analysed by using Grey correlation analysis. It was found that the correlation between the simplified steel content \(t/D\) and the ultimate bonding strength was the greatest. Formulas for the ultimate bonding strength and the critical lapping length for the steel bar fracture were proposed considering the grouting defect coefficient \(\omega\). The theoretical calculation results agreed well with the test results.