# Validity of Anchorage Zone Design for Post-Tensioned Concrete Members with High-Strength Strands
## 4 Experimental Results and Analysis  
The stresses generated in the anchorage zone under pre-stressing force were investigated. Table 2 shows the bursting stress when the pre-stressing force was applied. The maximum bursting stress of all specimens occurred at 0.3 h from the end of the specimens, regardless of anchorage shape or anchorage zone reinforcement details. In Group A with variable anchorage shapes, the maximum bursting stresses of RH-2 and CH-2, which had two anchorages, were 0.66 MPa and 0.70 MPa, respectively. The maximum bursting stresses of RH-3 and CH-3, which had three anchorages, and those of RH-4 and CH-4, which had four anchorages, were 1.04 MPa, 1.08 MPa, 1.66 MPa, and 1.72 MPa, respectively. The maximum bursting stresses of the specimens with the circular anchorages were slightly higher than those of the specimens with the rectangular anchorages. However, the difference was approximately 4.5%, so there was no apparent influence on bursting stress according to anchorage shape. With the attached gauge location 0.3 h farther from the end of the specimens, the bursting stresses were 68% and 37% of the maximum bursting stress regardless of anchorage shape. From this observation, it was confirmed that the anchorage shape had no effect on bursting stress distribution in the anchorage zone. The bursting stresses of Group A on the various locations in the specimens are shown in Figure 7. For Group B with anchorage zone reinforcement details as the variable, the maximum bursting stresses of Specimens CS2-3 and CS2-4 reinforced by Type 2 details were the smallest, regardless of the number of anchorages. As shown in Figure 8, the maximum bursting stresses of specimens reinforced with U-shaped hairpins and specimens reinforced with Type 1 details increased by 8.96% and 11.71%, respectively, using two anchorages, and by 4.07% and 6.25% using three anchorages compared with the specimen reinforced by Type 2 details. Although the numbers of reinforcing rebars in the anchorage zones of Group B were the same, it was more effective to place the reinforcing bars up to 0.5 h from the end than to place the reinforcements with equal spacing in the anchorage zone. The experimental results were compared to the maximum bursting stresses calculated by the current design codes, as shown in Figure 9. The ACI code predicted the maximum bursting stress reasonably well for specimens pre-stressed with two or three strands, while it underestimated the maximum bursting stress by approximately 18% for specimens using four high-strength strands. The AASHTO code overestimated the test results of specimens using two and three strands by an average of 17.3% and 14.1%, respectively, and underestimated the bursting stress of specimens using four strands by approximately 3.9%. This observation implied that the maximum bursting stress occurred 0.3 h from the end in the case of post-tensioned concrete members using high-strength strands; however, the equations in the design standards deal with conventional strands, so the maximum bursting stress was assumed to occur 0.5 h from the end. Additionally, the ACI 318-19 and AASHTO  
Figure 6: Test setup for two-point loading: (**a**) Schematic test setup; (**b**) Photograph of test setup. The strains due to bearing force when the pre-stressing force was introduced are summarized in Table 3. The maximum strain of all specimens occurred 0.15 h from the end of the members. In Group A, the difference between the bearing force of members with rectangular anchorages and that of those with circular anchorages was 3% when two tendons were applied. The differences in bearing force were 19% and 13% when three and four tendons were applied, respectively. Therefore, the bearing force was greater with rectangular anchorages than with circular anchorages. The strain increased when the number of tendons increased, but the maximum strains of Specimens RH-4 and CH-4 were 0.00135 and 0.0012, respectively, which are smaller than the maximum compressive strain of concrete.