# Validity of Anchorage Zone Design for Post-Tensioned Concrete Members with High-Strength Strands
## 3 Experimental Section  
### Specimen Details  
This study analyzed the stress in the anchorage zone of post-tensioned concrete members using unbonded high-strength strands, verified the bursting force and bearing force equations, and also evaluated the methods of design for reinforcing bars in anchorage zone set down in the ACI 318-19 and AASHTO codes. Because many studies have confirmed that the shape of the anchorage affects the bursting force generated in the anchorage zone, this study investigated members with rectangular and circular anchorages. In addition, this study considered the number of strands as a variable to confirm the effect of the number of strands on stress distribution in the entire cross-section. The ACI 318-19 code specifies that the anchorage zone for members using a general shape for the anchorage and mono strand should be reinforced with closed stirrups and a U-shaped hairpin. The test specimens were reinforced by closed stirrups or U-shaped hairpins according to ACI 318-19 requirements.  
The dimensions of the specimens were 750 mm \(\times\) 350 mm \(\times\) 4000 mm. The compressive strength of the concrete used for fabrication of the specimens was 35 MPa, and the main rebar was a D13 deformed bar with a yield strength of 400 MPa. The ACI 318-19 specifies the use of the minimum bonded reinforcement in a post-tensioned member with unbonded tendons in order to ensure flexural performance. The minimum area of bonded deformed longitudinal reinforcement \(A_{s,min}\) was calculated by multiplying the area of the cross-section between the flexural tension face and the centroid of the gross section \(A_{ct}\) by 0.004. Four tensile rebars and two compressive rebars with yield strengths of 400 MPa and diameters of 13 mm were placed to meet the minimum requirement for bonded reinforcement. To prevent shear failure, minimum shear reinforcement was required when \(V_{u}\) was greater than 0.5\(\varnothing V_{c}\). The stirrups were designed to use a D10 deformed bar and were arranged with 200 mm spacing according to the minimum shear reinforcement area and maximum spacing of shear reinforcement in ACI 318-19. The number and placement of anchorage zone reinforcements followed the ACI 318-19 requirements. All specimens were pre-stressed with Grade 2400, and had seven wires of 15.2 mm diameter and 138.7 mm\({}^{2}\) cross-sectional area. The yield strength of Grade 2400 was 2160 MPa, and the tendon profile was parabolic with 120 mm eccentricities. The details of specimens are summarized in Table 1. Group A classifies the test specimens by anchorage shape, whereas Group B classifies the test specimens according to anchorage zone reinforcement details. Figure 2 shows the notation of the specimens, and Figure 3 shows the details of the specimens.  
Figure 2: Notations of specimens.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Group** & **No** & **Specimen** & \(\dot{f_{c}}\) & \(f_{y}\) & \(f_{pu}\) & **Anchorage** & **EA** & **e** & **Anchorage Zone** \\  & & & **(MPa)** & **(MPa)** & **(MPa)** & **Shape** & **EA** & **mm** & **Reinforcement** \\ \hline \multirow{4}{*}{A} & 1 & RH-2 & & & & Rectangular & 2 & & & \\  & 2 & CH-2 & & & & Circular & 2 & & \\  & 3 & RH-3 & & & & Rectangular & 3 & & \\  & 4 & CH-3 & & & & Circular & 3 & & \\  & 5 & RH-4 & & & & Rectangular & 4 & & \\  & 6 & CH-4 & & & Circular & 4 & & \\ \hline \multirow{4}{*}{B} & - & CH-3 & & & & & 3 & & Hairpin \\  & 7 & CS1-3 & & & & 3 & & Stirrup (Type1) \\  & 8 & CS2-3 & & & & 3 & & Stirrup (Type2) \\ \cline{1-1} \cline{2-10}  & - & RH-4 & & & & 4 & & Hairpin \\  & 9 & CS1-4 & & & & 4 & Stirrup (Type1) \\  & 10 & CS2-4 & & & 4 & & Stirrup (Type2) \\ \hline \hline \end{tabular} \(f_{c}^{c}\): compressive strength, \(f_{y}\): yield strength, \(f_{pu}\): tensile strength of strand, e: eccentricity of strand.  
\end{table}
Table 1: Details of experimental specimens.  
Figure 3: _Cont._Figure 3: _Cont._  
Figure 3: \(Cont\).