# Deep Embedment (DE) FRP Shear Strengthening of Concrete Bridge Slabs under Loads Close to Supports
## 4 Discussion of Test Results
### Strain Response  
Figure 12 presents the curves of the load versus the maximum compressive strain of concrete slabs for the test specimens. It was observed that the curves have the same tendency for all the test specimens before the applied load reached the around 130 kN. This loading corresponds to the shear failure load of the unstrengthened test slab. Due to shear failure of the concrete slabs, the maximum compressive strain of concrete in the unstrengthened slab did not reach the crush strain (0.003) at the ultimate load. As the applied load increased, the compressive strain of all the strengthened test slabs increased more than the crush strain of concrete (0.003). It is noted that the failure mode of strengthened concrete slabs is flexural failure with concrete crush, which can be found in the observation of the test results (see Figure 10).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**RP * (\%)**} & \multirow{2}{*}{**fcu (MPa)**} & \multirow{2}{*}{**EBT ***} & \multicolumn{2}{c}{**Diameter of**} & \multicolumn{2}{c}{**Increase in DF**} \\  & & & & & **Embedment** & **DF** & **Compared to** \\  & & & & & **Bar/Hole (mm)** & & **S-Con Beam (\%)** \\ \hline S-Con & 1.1 & 24.5 & N/A & N/A & N/A & 7.7 & N/A \\ S-D-1 & 1.1 & 27 & N/A & N/A & -/16 & 6.54 & \(-\)15\% \\ S-S-2-10 & 1.1 & 24.5 & Steel & 2 \(\times\) 2 & 10/16 & 28.67 & 272\% \\ S-B-2-9 & 1.1 & 25.1 & BFRP & 2 \(\times\) 2 & 9/16 & 23.03 & 199\% \\ S-G-2-9 & 1.1 & 25.6 & CFRP & 2 \(\times\) 2 & 9/16 & 23.05 & 199\% \\ S-C-2-9 & 1.1 & 25.3 & CFRP & 2 \(\times\) 2 & 9/16 & 25.01 & 225\% \\ S-C-1-9 & 1.1 & 25.4 & CFRP & 2 \(\times\) 1 & 9/16 & 20.79 & 170\% \\ S-C-1-13 & 1.1 & 25.8 & CFRP & 2 \(\times\) 1 & 13/20 & 25.44 & 230\% \\ \hline \hline \end{tabular}  
* RP = Reinforcement percentage; ** EBT = Embedment bar type; *** ESC = Embedment strengthening configuration; DF = Deformation factor.  
\end{table}
Table 3: Deformability factors of all the test slabs.  
Figures 13 and 14 illustrate the relationship of applied load and maximum tensile strain in longitudinal steel reinforcement and embedment strengthening bars. It can be seen in Figure 13 that all the curves of load versus maximum tensile strain in steel reinforcement have a similar tendency for all the test specimens. This means that using the deep embedment strengthening method does not have a strong effect on the contribution of steel reinforcement to the ultimate capacity of the concrete slabs. Examination of the curves in Figure 14 reveals that none of the deep embedment strengthening bars contributed to the loading carrying capacity before they reached the shear cracking load (around 100 kN). All the strain values reported in this paper are the maximum measured values. After the applied load increased beyond 100 kN, the strain in the deep embedment bars started to increase to a large value (see Figure 14), the level at which the concrete slabs failed. It can be summarised that the deep embedment strengthening material started to contribute to shear resistance after the formation of the concrete struts in the shear behaviour. After the embedment bars started to contribute to the shear capacity, the strain in all the test slabs was increased with a constant slope. Additionally, the maximum strain value of steel embedment bars at failure is smaller than those in embedment FRP bars, which could be due to the larger stiffness in steel bars compared to the FRP materials.  
Figure 12: Applied load vs. maximum compressive strain of concrete slabs.  
Figure 13: Applied load vs. maximum tensile strain in longitudinal reinforcement.