###### Abstract  
This study aimed to evaluate the bearing strength of the post-tensioning anchorage zone with respect to the relative bearing area and lateral confinement design of spiral and stirrup rebars. Eleven specimens were fabricated and tested to fracture in accordance with EAD 160004-00-0301. Load-displacement curves and fracture modes were analyzed. Then, the conventional design equation for the bearing strength and previous findings on the relative bearing area was re-investigated in comparison with the test results. From the test, the representative findings are as follows: (1) A specimen with relatively small size and less lateral reinforcement is more likely to be affected by the wedge action of the anchorage device; however, a larger specimen is affected by both concrete crushing and/or spalling; (2) The behavior of the anchorage zone is markedly affected by the local behavior near the anchorage bearing plate, and the sectional efficiency is mostly determined by \(A/A_{g}\); (3) For specimens with \(A/A_{g}=9.52\), the proportional limit of the load-displacement curve is determined by the yield of spiral rebar or fracture of the bearing plate, but the later part of the curve is determined by lateral confinement; (4) The maximum \(A/A_{g}\) that could produce 100% sectional efficiency is about 2.0 for the anchorage bearing plate used in the test; (5) For a fully confined specimen with a small-diameter spiral for minimum anchorage spacing, the stirrup rebar design mainly influences crack occurrence and patterns when the size of the specimen is equal to the minimum anchorage spacing; however, the area of the load-displacement curve after the proportional limit as well as crack occurrence and patterns are also influenced by stirrup rebar design when \(A/A_{g}\) is relatively large; (6) Finally, a revised design model is proposed to effectively estimate the ultimate bearing strength of the post-tensioning anchorage zone without respect to \(A/A_{g}\). 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. post-tension; anchorage zone; bearing strength; relative bearing area; minimum anchorage spacing +
Footnote †: journal: Applied Sciences  
enhance its compressive strength. Stirrup rebars resist the bursting force by the wedge action of the anchorage device. Several studies have investigated anchorage zone behavior. [PERSON] and [PERSON] [2] found that reinforcement with spiral rebar was the most effective anchorage zone confining method, but that it was not effective if it did not cover the appropriate length. [PERSON] and [PERSON] [3] studied the failure modes of local anchorage zones according to reinforcement details and found that failures occurred by (1) splitting in an under-reinforced specimen; (2) concrete crushing beneath the anchorage device in cases of spiral reinforcement; and (3) cone-shaped wedge action in the transition zone between the local and general zones where the prestressing force spreads out over the entire cross-section. [PERSON] [4] and [PERSON] [5] proposed a design model, which is based on the work of [PERSON] et al. [6]. The design model allows to consider the favorable confinement effect; thus, the estimated bearing strength is higher. They suggested a confining pressure limit of 8.3 MPa based on the results of [PERSON] and [PERSON] [2]. [PERSON] et al. [7] proposed a modified analysis approach for the interior anchorage zone of post-tensioned concrete structure, but their study focused on the bursting behavior of the anchorage zone. [PERSON] and [PERSON] [8] analyzed anchorage zone performance based on nonlinear numerical analysis in comparison with the design model of [PERSON] and [PERSON] [5]. The study revealed that the design model of [PERSON] and [PERSON] [5] should not be applied to cases that have not been confirmed by testing.