# Validity of Anchorage Zone Design for Post-Tensioned Concrete Members with High-Strength Strands
## 5 Conclusions  
In this study, an experiment with ten post-tensioned specimens was performed with the parameters of anchorage shape, number of strands, and details of anchorage zone reinforcement. The stresses generated in the anchorage zone during the introduction of pre-stressing force and under ultimate flexural load were analyzed, and the design methods specified by the design standards were verified. The main conclusions from the study are as follows:  
1. The maximum bursting stress occurred at 0.3 h from the end of members, and the distribution aspect of bursting stress in the anchorage zone was similar regardless of anchorage shape when the pre-stressing force was introduced. The design standards assumed that the maximum bursting force occurs at 0.5 h; in addition, the bursting force was estimated as the summation of the tensile forces without considering the offsetting of the bursting stress due to an increased number of strands.
2. The strain due to the bearing force of a member with circular anchorages was 12% smaller than that of a member with rectangular anchorages because the circular anchorage efficiently distributed the bearing force when the pre-stressing force was introduced. As the number of strands increased, the strain due to bearing force increased proportionally. The hairpin reinforcement resisted the bearing force most effectively. The transverse spacing of the stirrups was the main variable in resisting the bearing force when reinforcement used closed stirrups.
3. The allowable bearing forces calculated by the ACI and AASHTO codes were about 241 kN and 493 kN, respectively, when pre-stressing force was introduced by 320 kN. The ACI code estimated the allowable bearing force to be smaller than the pre-stressing force regardless of anchorage shape. However, the experimental results showed that cracking and failure of the concrete did not occur due to failure to reach the maximum compressive strain. The AASHTO code estimated the allowable bearing force to be approximately 1.5 times the pre-stressing force; this is not suitable for building structures, which have members that are relatively small compared to civil structures.
4. The results of the flexural experiment confirmed that additional stress occurred in the anchorage zone as the flexural load increased, which may have been caused by a failure of the anchorage zone; in addition, the circular anchorages were more effective than rectangular anchorages at dispersing increasing bursting and bearing force when flexural load was applied. The concrete strain estimated by bursting force and bearing force was smaller by 40% and 203% on average when applying circular anchorages rather than rectangular anchorages. The anchorage reinforcement designed using current codes could not resist the increased stress. Therefore, design standards should consider a method for anchorage zone reinforcement under ultimate flexural load.  
[PERSON] conceived the study concepts, designed and carried the experiment, analyzed the experimental results, and took charge of the entire manuscript; [PERSON] and [PERSON] assisted with the integrity of the entire study, provided the crucial intellectual support, and revised the manuscript. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2020R1A2C2009351).  
The authors declare no conflict of interest.