## 6 Conclusions  
In this study, the bearing strength, load-displacement curve, and fracture modes of the post-tensioning anchorage zone were investigated based on load-transfer tests of 11 specimens, using variables of the relative bearing area (\(A/A_{g}\)), confinement effect of spiral rebar design, and additional confinement effect of stirrup rebars. The following conclusions were drawn through an analysis of the test results:  
1. A specimen with relatively small dimensions and less lateral reinforcement is more likely to be affected by the wedge action of the anchorage device. However, a specimen with \(A/A_{g}\geq 4.50\) is affected by both concrete crushing and/or spalling;
2. For specimens with a small-diameter spiral for minimum anchorage spacing, the strength varies by about 30% depending on \(A/A_{g}\), and the effect of the additional bearing area on the ultimate bearing strength is influenced by lateral confinement. In addition, the behavior of the anchorage zone is highly affected by the local behavior near the anchorage bearing plate, and the sectional efficiency is mostly determined by \(A/A_{g}\). In the tests, it varied from about 20% to 110%, mostly depending on \(A/A_{g}\);
3. For anchorage zone specimens with \(A/A_{g}=9.52\), the proportional limit of the load-displacement curve is determined by the yield of the spiral rebar or fracture of the bearing plate, but the latter part of the curve is determined by lateral confinement;
4. The bearing strength can increase by over 50% depending on the lateral rebar design, but the rate of increase in strength decreases for specimens with relatively small \(A/A_{g}\);
5. The effect of lateral confinement is determined by the combined effect of both lateral pressure and confined area;
6. The maximum \(A/A_{g}\) that can produce 100% sectional efficiency is about 2.0 for the anchorage bearing plate used in this test;
7. For specimens that are fully confined with small-diameter spirals for minimum anchorage spacing, the stirrup rebar design mainly influences crack occurrence and patterns when \(A/A_{g}\) is relatively small. However, not only the crack occurrence and pattern but also the section of the load-displacement curve after the proportional limit is influenced by stirrup rebar design when \(A/A_{g}\) is relatively large;
8. The design model by [PERSON] [4; 5] was reconstructed for the special anchorage bearing plate, and coefficients were proposed to consider the effect of \(A/A_{g}\) and lateral confinement of a specimen larger than the minimum anchorage spacing. The comparison between the test results and the results of previous design equations verified the efficiency and accuracy of the proposed equation;
9. From the comparison of the design equations, it was concluded that the proposed equation provides a more reliable prediction with a 14.0% average error rate and 5.7% standard deviation of error rate. \begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & 11 – \
\begin{tabular}{c} _Equations (6–8)_ \\ _Test Result_ \\ \end{tabular} & 11 –
\begin{tabular}{c} _Equations (6),(20),(20)_ \\ _Test Result_ \\ \end{tabular} \\ \hline A12H-1 & 29\% & 14\% \\ A12H-2 & 30\% & 15\% \\ A12H-3 & 26\% & 11\% \\ A12H-4 & 26\% & 19\% \\ A12H-5 & 7\% & 8\% \\ A12H-6 & 14\% & 7\% \\ A12H-7 & 7\% & 9\% \\ A12H-8 & 0\% & 9\% \\ A12H-9 & 2\% & 22\% \\ A12H-10 & 1\% & 16\% \\ A12H-11 & 38\% & 24\% \\ \hline Average & 16.2\% & 14.0\% \\ Standard deviation & 13.7\% & 5.7\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Error rate comparisons between design equations. In the future, the proposed design model will be compared with various anchorage and various reinforcement conditions used in post-tension work in the field and improved continuously as an anchorage zone design model. Conceptualization, J.-K.K. ; methodology, J.-M.Y. ; writing--original draft preparation, J.-K.K. ; writing--review and editing, J.-M.Y. ; validation, J.-K.K. and J.-M.Y. ; investigation, J.-K.K. and J.-M.Y.