# Deep Embedment (DE) FRP Shear Strengthening of Concrete Bridge Slabs under Loads Close to Supports
## 4 Discussion of Test Results
### Load vs. Deflection Responses  
Figure 11 shows the curves representing the load versus the maximum vertical deflection (T3 as shown in Figure 8a) at the loading position for all the test slabs. For the untrengthened test slabs, the bilinear behaviour of the load-deflection curves is characteristic of a shear failure. The first part of this curve is up to flexural crack load (around 25 kN), while the second part represents the crack slab with reduction stiffness. When the applied load reached the shear capacity, the applied load was terminated suddenly. This corresponds to the observation of the test process (see Figure 10). Before the applied load reached the shear capacity of the concrete slabs, the behaviour of the load-deflection response of the strengthened test slabs was similar to that of the untrengthened test slabs, see Figure 11. As the load increased, the application of the deep embedment shear strengthening method resulted in  
Figure 11: Comparisons of load vs. vertical deflection at loading point in test slabs.  
higher ductile structural response compared to the unstrengthened test slabs. Figure 11 reveals that the strengthened specimens showed a greater overall stiffness compared with the S-Con and S-D-1 slabs. Using this strengthening scheme, the test specimens strengthened with deep embedment bars, which reached their flexural capacity (see Figure 11), failed in a ductile manner. Therefore, the slabs with deep embedment strengthening methods exhibited a higher deflection at the loading point and maximum load at failure compared to unstrengthened test slabs (see Figure 11).  
Generally, the ductility of reinforced concrete flexural components can be considered as the ability to sustain inelastic deformation without degeneration of loading-carrying capacity before structural failure. Based on this theoretical assumption, deformation or energy absorption can be defined as structural ductility. For steel reinforced concrete flexural components, ductility can be expressed as the ratio of ultimate deformation to deformation at yield. Therefore, the ductility of all the test slabs can be evaluated by means of a deformation factor (DF) [17]. This factor is defined as a ratio of the energy absorption at failure (area under load-deflection curve up to ultimate load) to that at service load (at the serviceability deflection limit of span/800 [18]). The results of DF values for all the test slabs are listed in Table 3. It was found that the embedment strengthening method improved the ductility of the strengthened test slabs significantly as reported in the test results of deep embedment strengthening concrete beams [6; 7]. As shown in Table 3, it can be seen that using this strengthening scheme resulted in increasing the DF values by around 200%. This suggests that the ductility of concrete slabs subjected to loads close to the support is enhanced significantly by deep embedment strengthening methods. As expected, the concrete slabs strengthened with deep embedment steel bars attained the largest DF of 28.67, due to having the highest strengthening stiffness. As shown in Table 1, the decrease in stiffness of strengthening materials results in slightly smaller DF values of strengthened concrete slabs.