# Experimental and Theoretical Study on Anchorage Loss of Prestressed CFRP-Reinforced Concrete Beams
## 3 Experimental Study  
### Overview of Project  
To study the anchorage loss before and after tensioning, to continuously monitor the long-term prestress loss, and to analyze the proportion of anchorage loss in the total prestress loss, this paper conducted an experimental study on the prestressed reinforcement of concrete beams. Figure 13 shows the prestressed CFRP tendon-main beam connection system: the anchor and the steel reaction frame were connected through the internal thread at the end of the anchor and the connecting screw rod, and the steel reaction frame was connected to the bottom of the beam through anchoring screws (embedded depth of 170 mm). The steel reaction frame served two different purposes at its ends: one end was used as the fixed end, where a through-type pressure sensor was installed to monitor the magnitude of prestress and prestress loss; the other end was used as the tensioning end, where a hydraulic jack was placed to apply prestress to the CFRP tendons. Note that the CFRP tendons used in this reinforcement system had a smooth surface, a diameter of 12 mm, and an elastic modulus of 160 GPa, and the anchorages were physical connection anchorages with high anchorage efficiency. Subsequent experiments disregarded the relative slippage between the anchorage and the CFRP tendons.  
To validate the reliability of the FEM model and the TCS mentioned above, seven CFRP tendons were selected as test objects, consisting of one control group and six variable groups. The experimental conditions were modified by adjusting factors such as the dimensions of the front steel plate, prestress magnitude, length of the connecting screws, and torque applied to the fixed nuts, as detailed in Table 3. Each condition was tested twice, and the average result was recorded.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **CFRP Tendon Length** & **Prestress** & **Connecting Screw Length** & **Side Panel Spacing** & **Fixed Nut Torque** \\  & **L (mm)** & **(MPa)** & **y\({}_{1}\) (mm)** & **(mm)** & **(N\(\cdot\)m)** \\ \hline
1 & 12,000 & 950 & 139 & 79 & / \\
2 & 12,000 & 950 & 135 & 59 & 400 \\
3 & 12,000 & 950 & 137 & 59 & / \\
4 & 12,000 & 475 & 374 & 59 & 400 \\
5 & 12,000 & 475 & 370 & 59 & / \\
6 & 12,000 & 950 & 374 & 59 & 400 \\
7 & 12,000 & 950 & 376 & 59 & / \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test conditions.  
Figure 13: Schematic diagram of the arrangement of prestressed CFRP tendons at the bottom of the beam (unit: mm).  
By using the tensioning method described in Section 2.1, the prestress \(\sigma_{\text{a}}\) is recorded before tightening the fixed nuts, and after removing the jack, the prestress \(\sigma_{\text{b}}\) is recorded. The difference between \(\sigma_{\text{a}}\) and \(\sigma_{\text{b}}\) represents the anchorage loss of the prestressed CFRP tendons \(\sigma_{\text{l}}\), which is essential for subsequent data analysis. Two points require attention.  
1. Accurately controlling the length of the connecting rods is challenging in engineering. To examine the impact of varying connecting rod lengths on anchorage loss, pre-tensioning force was applied before the official tensioning of CFRP tendons. The length of the connecting screws at this stage was then measured for subsequent calculations.  
2. To study the effect of thread clearances on prestress loss, groups 3, 5, and 7 required additional locking with a pipe wrench after normal tightening to minimize gaps. During fixing, all groups simulated actual construction workers tightening the nuts. For groups 3, 5, and 7, a specific torque was applied with an electric torque wrench as a control.