## 6 Pullout Strength of GFRP Bars
Three HSS sections were stacked on top of one another on one side of the bar and in a parallel fashion on the opposite side of the bar, all of which were resting on four square metal plates. On top of these six HSS sections were two longer HSS sections, which were perpendicular to the supporting HSS members, while the GFRP bar of interest was centered between them. On top of these two sections is a series of plates, a rubber pad, a load cell, a hydraulic jack, and pull-out grips. This setup is demonstrated in Figure 18. Once the rigorous steel setup is complete, a potentiometer (POT) was placed adjacent and connected to the bar, while the tip of the needle was on the top of the concrete, as shown in Figure 18.  
Figure 17: Installation procedure for postinstalled GFRP bars: (**a**) Postinstalled holes after drilling: (**b**) Cleaning of postinstalled barrier anchor holes; (**c**) Injecting epoxy into the drilled hole; (**d**) Installing the GFRP bar while slowly rotating left and right; (**e**) Final view of the preinstalled bars in the slab. Figure 18: Pullout test setup. Test results showed that the straight bars failed primarily due to bar crushing at the grip location to the extent that the part split laterally along the free-standing length between the grips and the top of the concrete slab, as depicted in Figure 19a. Although the bars did not manage to achieve their nominal ultimate tensile capacity, and the bar did not visually appear to slip out of the concrete, the test results showed an average pullout force of 146.76 kN, as listed in Table 4, which is about 73% of the tension capacity of the bar. After pullout tests, concrete core samples were taken at the bar location, as shown in Figure 19b. Subsequently, the core samples were sliced in half using a concrete saw, as shown in Figure 19c. The intent of slicing the samples directly in half (cutting the GFRP bar in half as well) was to examine whether any slippage or other forms of failure within the concrete matrix occurred during the test. Figure 19d shows that the bar had no visual slippage at its end in the concrete slab. The bar appeared to be fully bonded to the concrete surrounding after the test. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type of** & **Group** & **Embedment** & **No. ** & **Failure Load** & **Average** & **Type of** \\
**Construction** & **Group** & **Length (mm)** & **No. ** & **(kN)** & **Failure Load** & **Failure** \\ \hline \hline \multirow{6}{*}{ \begin{tabular}{c} Preinstalled \\ bars \\ (2): \\ \end{tabular}  } & & & A & \(150.88\) & & Bar crushing \\ \cline{3-6}  & & & B & \(146.02\) & \(146.76\) & \( \begin{array}{c}\text{Bar crushing}\\ at the grip \\ \end{array} \) \\ \cline{3-6}  & & & C & \(144.67\) & \( \begin{array}{c}\text{STDEV}=2.80\end{array} \) & \( \begin{array}{c}\text{Bar crushing}\\ at the grip \\ \end{array} \) \\ \cline{3-6}  & & & D & \(145.48\) & & Bar crushing \\ \cline{3-6}  & & & A & \(157.89\) & & Bar crushing \\ \cline{3-6}  & & & B & \(161.94\) & \( \begin{array}{c}\text{STDEV}=8.46\end{array} \) & \( \begin{array}{c}\text{Bar crushing}\\ at the grip \\ \end{array} \) \\ \cline{3-6}  & & & C & \(151.69\) & \( \begin{array}{c}\text{STDEV}=8.46\end{array} \) & \( \begin{array}{c}\text{Bar crushing}\\ at the grip \\ \end{array} \) \\ \cline{3-6}  & & & D & \(142.51\) & & Bar crushing \\ \cline{3-6}  & & & D & \(142.51\) & & Bar crushing \\ \cline{3-6}  & & &  
Test results showed that the headed-end bars with a fully bonded straight portion failed primarily due to bar crushing at the grip location to the extent that the part split laterally along the free-standing length between the grips and the top of the concrete slab. Despite the bars failing to reach their nominal ultimate tensile capacity and the absence of any visible slippage from the concrete, the test results indicated an average pullout force of 153.5 kN, representing approximately 76% of the bar's tension capacity. Table 4 summarizes the pullout capacity of each bar in Group 2, along with the corresponding mode of failure.